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Composition-Climate Interactions including natural aerosols

Chemistry and aerosols play a major role in determining surface air quality, the Earth’s energy budget, and climate change. Conversely, climate change affects atmospheric abundances of trace gases and aerosols through composition-climate interactions. This session focuses on global scale atmospheric chemistry and aerosol modelling, radiative forcing, and climate change through the historical period and into the future.
A better understanding of the role of natural aerosols in the atmosphere is essential for assessing climate changes. Our session explores primary aerosols and those formed from precursor gases emitted by natural sources, e.g. from wildfires, deserts, volcanoes, oceans, and vegetation. The session intends to bring together experts from different fields to assess the state-of-the-science knowledge on natural aerosols and to identify future directions to reduce uncertainty in their emissions and impacts. We encourage submissions that use models across different spatial scales and consider past, present or future perspectives, as well as measurements from remote sensing, field campaigns and laboratory experiments.

In particular, it aims to bring together scientists with an interest in:

1. Evaluating reactive gases and aerosols in models against observations

2. Quantifying the impact of emissions changes on atmospheric composition

3. Exploring chemistry-climate interactions in models, with a focus on climate feedbacks involving trace gases and aerosols

4. Quantifying radiative forcing and the climate response to changes in trace gas and aerosol concentrations

5. Distinguishing between truly natural aerosols and those whose emissions or formation are influenced by anthropogenic activities

6. Missing links in our understanding of the lifecycle of natural aerosols

7. The time evolution of contributions of natural aerosols to atmospheric composition and deposition
8. The consequences of changes in natural aerosols

The session welcomes contributions from those currently involved in analysis of recent and ongoing CMIP6 experiments focusing on the areas above,

Co-organized by CL2
Convener: William Collins | Co-conveners: Paul Griffiths, Fiona O'Connor, James KeebleECSECS, Christopher SmithECSECS, Stephanie Fiedler, Catherine Scott, Douglas HamiltonECSECS, Kerstin Schepanski
| Mon, 23 May, 08:30–11:40 (CEST), 13:20–14:33 (CEST)
Room M1

Mon, 23 May, 08:30–10:00

Chairpersons: William Collins, Christopher Smith, James Keeble

Susanne Bauer

Climate change is the result of individual forcing agents changing their radiative balance at the top of the atmosphere over time, and as a result, if positive radiative forcings dominate over negative forcings, the troposphere warms. Over the historical period, based on the CMIP6 simulations ranging from 1850 until 2014, aerosol effects via their ability to absorb or scatter solar radiation and alter clouds, have provided the largest negative forcings compared to all other forcings and played an important role in counterbalancing some of the greenhouse gas (GHG) caused global warming. Trends in aerosol have been very diverse globally, depending on source and geographical region. While many regions in the Northern Hemisphere have been seeing decreasing emissions since decades, changes in Asia have been more recent, with some countries, such as China have recently reversed their trends and now have decreasing emissions, while other regions, such as India or parts of South Asia, e.g., are still on an increasing trajectory.

Here we study aerosol forcing trends in the CMIP6 simulations of the GISS ModelE2.1 coupled ocean climate model using a fully coupled atmosphere composition configuration, including interactive gas-phase chemistry, and either an aerosol microphysical (MATRIX) or a mass-based (OMA) aerosol module. The historical (1850-2014) CMIP6 as well as four Shared Socioeconomic Pathways (SSP) simulations (2015-2100) are analyzed, including the future scenarios, SSP1-2.5, SSP2-4.5, SSP3-7.0 and SSP 5-8.5.

The main conclusion of this study is that aerosol forcings have reached their turning point, switching from globally increasing to decreasing trends, in the first decade of the 21st century. The turning point in aerosol direct forcing does depend on the individual SSP and model used, however forcings caused by aerosol cloud interactions fall under all studied scenarios into the historical period. The fact that aerosol-cloud forcings dominate in magnitude over direct forcings, leads to the conclusion that the turning point of total aerosol forcings has already been reached. As a consequence, it could be possible that the recently observed global warming which is primarily driven by greenhouse gases has been augmented by the effect of a decreasing aerosol cooling effect on the global scale.



How to cite: Bauer, S.: The turning point of the aerosol era, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1128, https://doi.org/10.5194/egusphere-egu22-1128, 2022.

Elli Mastakouli (1) et al.


Sea salt (SS) are natural strongly scattering coarse aerosols, which yield the largest fraction of aerosol burden over many places on the Earth. They are important to the physics and chemistry of the marine atmosphere, affecting visibility, remote sensing, atmospheric chemistry, and air quality. The production, entrainment, transport and removal of SS aerosol are affected by several meteorological and environmental factors, such as wind speed, surface ocean and air temperature, relative humidity, atmospheric stability, precipitation and sea bottom depth and topography. The key meteorological factor that governs the SS production and life cycle is wind, which causes waves to break, forming whitecaps, thus influencing the injection of SS to upper atmospheric levels and their horizontal transport. Although, most of SS aerosols can be transported with atmospheric circulation only to short distances from their sources, the relatively smaller bubbles can live for a longer time in the atmosphere and thus can be transported not only over oceanic, but also over adjacent continental areas. Sea salt aerosols are highly hygroscopic, adsorbing water, and thus behave as Cloud Condensation Nuclei (CCN), affecting the formation, physical and optical properties of clouds. Therefore, their quantification and spatiotemporal variability is essential for the accurate determination of their climatic ole.

In the present study, SS aerosols are detected on a global scale and for the 16-year period from 2005 to 2020, using a satellite algorithm, which is based on aerosol optical properties. This algorithm uses as input daily spectral Aerosol Optical Depth (AOD) and Aerosol Index (AI) or single scattering albedo (SSA) data from MODIS C6.1 and OMI OMAERUV databases, respectively.  It operates on a daily basis and 1°×1° pixel level and detects the presence of SS aerosols by applying suitable thresholds on Ångström Exponent (AE) (calculated using spectral AOD from MODIS) and AI or SSA. The algorithm outputs the absolute and relative frequency of occurrence of SS aerosols, as well as the associated AOD, on a monthly and annual basis. The results are given on a pixel as well as on regional and global scales. By running the algorithm for each year of the study period, the climatological mean values and the interannual variability and trends of the frequency of occurrence and AOD of SS aerosols are estimated.

How to cite: Mastakouli (1), E., Gavrouzou (1), M., Korras-Carraca (1,2), M.-B., and Hatzianastassiou (1), N.: A global climatology (2005 – 2020) of sea salt aerosols using MODIS and OMI satellite data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7346, https://doi.org/10.5194/egusphere-egu22-7346, 2022.

Michael Pikridas et al.

This study analyzes the optical properties (scattering, absorption coefficients, single scattering albedo) of aerosols in the marine boundary layer of oceanic areas surrounding the East Mediterranean – Middle East (EMME) region. It aims  to explore the spatio-temporal variability of aerosols, their atmospheric mixing state, sources and dominant types in a way to assess their role on solar radiation and climate. The current analysis uses measurements obtained in the framework of the AQABA (Air Quality and climate change in the Arabian Basin) cruise, during a two month (1st July - 1st September 2017) period. The cruise consisted of a round trip onboard of a research vessel from south of France to Kuwait, crossing the central-east Mediterranean Sea, Red Sea, Arabian Sea and Persian Gulf.

Aerosol scattering and absorption coefficients of both submicron (PM1) and supermicron (PM10) particles were measured, using a polar nephelometer (Aurora 4000 Ecotech Inc) and a dual spot aethalometer (Model AE-33, Magee Scientific), respectively. The meterorological and atmospheric conditions during the whole cruise campaign in July-August 2017 were consisted with local and regional climatology, without intense dust outflows from the arid/desert lands in the Middle East. FLEXPART air mass back-trajectories indicated the potential impact of the continental emissions to examined oceanic regions.

Both scattering and absorption coefficients for PM1 and PM10 particles exhibited higher values along the ship cruise in the southern Red Sea, due to continental outflow from east Africa, and in the Persian Gulf due to mixing of natural dust with anthropogenic emissions from the industrial sector and oil refineries. The east Mediterranean exhibited moderate aerosol loading, with intermediate values of scattering Ångström Exponent (SAE) (around 1-1.5), which increased over the Persian Gulf, suggesting enhanced anthropogenic impact against desert dust, while over the Gulf of Aden and the west Arabian Sea, SAE values were very low revealing dust dominance. The absorption Ångström Exponent (AAE) values remained close to 1, indicative of Black Carbon from fossil-fuel combustion, while they increased at regions dominated by dust aerosols, even without high aerosol loading i.e. in the Gulf of Aden and the Arabian Sea.

Using the SAE vs. AAE classification scheme, key aerosol types were identified along the ship cruise. The results showed contrasting aerosol characteristics and types for the various sub-regions. The “BC-dominated” type clearly prevailed over the East Mediterranean and Suez Canal, while coarse particles mixed with BC dominated in the Gulf of Aden and the Arabian Sea, where the “dust type” also appeared. In the Persian Gulf, the mixing of anthropogenic pollution with marine aerosols, resulted in a dominant “small/low absorption” aerosol type, characterized by fine aerosols with low spectral dependence of the absorption coefficient.   

How to cite: Pikridas, M., Kaskaoutis, D., Mihalopoulos, N., Barbounis, K., Lelieveld, J., and Sciare, J.: Optical properties and dominant types of aerosols in the marine environments surrounding the East Mediterranean - Middle East (EMME) region during the AQABA cruise, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9201, https://doi.org/10.5194/egusphere-egu22-9201, 2022.

Stavros Solomos et al.

The proper representation of dust production in numerical weather prediction (NWP) models depends largely on the detailed mapping of the arid areas that act as natural dust sources. The extend and the strength of these sources varies throughout the year based on aridity and vegetation properties. Such changes are monitored from spaceborne platforms (e.g. MODIS NDVI index). In this work we present a methodology for including a dynamic dust source map in the state-of-the-art NMME-DREAM and WRF-Chem models. This time-varying dust source map is based on the 1000m 16-day averaged Normalized Difference Vegetation (NDVI) from the MODIS/Terra instrument. The methodology is first tested with DREAM-NMM over the Arabian Peninsula. The results indicate significant improvement in simulated AODs over AERONET stations compared to the runs driven by the standard static dust source map. The modeled AOD bias in NMME-DREAM is improved from -0.140 to 0.083 for AOD>0.25 and from -0.933 to -0.424 for dust episodes with AOD> 1. Afterwards we apply the above methodology to the Air Force Weather Agency (AFWA) dust emission module in WRF-Chem model. WRF-Chem has been selected due to its nesting capabilities that permit finer resolution simulations of local scale dust processes. Two sets of simulations have been performed covering the entire Saharan desert, the Mediterranean, Europe and part of the Arabian Peninsula, at a horizontal resolution of 12×12 Km: (1) WRF-Chem control simulations, where dust sources are defined based on the original AFWA code and (2) WRF-Chem experimental simulations where the erodibility of the selected domain is modified based on MODIS NDVI. The selected test period is April 2017 when significant Saharan dust outbreaks took place over the Mediterranean. The simulated AOD from both sets of model runs are validated against AERONET stations. First results verify the successful implementation of the dynamic dust source module in WRF-Chem.  The experimental (NDVI) simulations showed an overall increase in dust loads over the entire domain and an improved performance, mostly in areas close to the Saharan desert.

How to cite: Solomos, S., Spyrou, C., Bartsotas, N., and Nickovic, S.: Development of a dynamic dust-source map for regional dust models based on MODIS NDVI , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1252, https://doi.org/10.5194/egusphere-egu22-1252, 2022.

Claire Moffett et al.

As the Arctic continues to change and warm rapidly, it is increasingly important to understand the contribution of biogenic sources to Arctic aerosol. Biogenic sources of primary and secondary aerosol in the arctic will be impacted by climate change, including warming and earlier snow and ice melt, while local emissions and long-range transport can drive changes in anthropogenic aerosol. This study focuses on identifying the contribution of biogenic aerosol to organic carbon (OC) and its seasonal trends through the analysis of aerosol chemical and isotopic composition. Aerosol samples were collected at two sites on the North Slope of Alaska (Utqiaġvik and Oliktok Point) over the summer of 2015 and from June 2016 through August 2017. Organic carbon concentrations correlated well between the sites with high contribution from contemporary sources. Backwards air mass trajectory analysis indicates that source regions are primarily marine in the summertime. Methanesulfonic acid (MSA) was utilized to confirm this marine influence. Secondary organic aerosol confirmed the contribution of terrestrial biogenic sources to organic aerosol at both sites. Strong correlations between ambient temperature and MSA and OC were found during the summer. This study provides a multiyear characterization of organic carbon highlighting the high biogenic influence and indicating areas of interest for future research.

How to cite: Moffett, C., Mehra, M., Barrett, T., Gunsch, M., Pratt, K., and Sheesley, R.: Biogenic aerosol composition on the North Slope of Alaska, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6424, https://doi.org/10.5194/egusphere-egu22-6424, 2022.

Ankur Bhardwaj and Ramya Sunder Raman

Measurement of ambient particulate organic carbon (OC) collected on quartz filters is susceptible to net positive artefacts (overestimation of particulate OC due to adsorption of volatile and semi-volatile organic compounds) while that collected on Teflon filters is susceptible to net negative artefacts (loss of particle OC due to volatilization). In this study, QbQ (Quartz behind Quartz) filter configuration was used for estimating positive artefact, while, QbT (Quartz behind Teflon) filters in conjunction with the QbQ were used to estimate OC volatilization from Teflon filters over a two-year (2019 and 2020) period in Bhopal, one of the eleven COALESCE (Carbonaceous Aerosol Emissions, Source Apportionment, and Climate Impacts) network sites in India. OC and EC measurements by thermal-optical carbon analyses on 748 samples (349 bare quartz (Q), 349 QbQ, and 50 QbT; 24 hours time-integrated) were used in this study. The results showed that the average adsorbed gaseous OC contribution to total OC measured on quartz filters was 17 % (0.9 µg m-3) and 11 % (0.6 µg m-3) during 2019 and 2020, respectively. Organics volatilization loss from Teflon filters as a fraction of measured PM2.5 mass were estimated by applying organic matter (OM)/OC ratios ranging between 1.7 and 2.0 to the OC measured on QbT filters. The annual mean volatilized OC  that was likely re-captured by bare quartz but lost from Teflon filters were 27 % (1.6 µg m-3) and 21 % (1.1 µg m-3) of the total OC measured during 2019 and 2020, respectively. Also, the average PM2.5 lost due to OM volatilization was 8 % (± 4 %) and 6 % (± 5 %) during 2019 and 2020, respectively. Our work shows that organic volatilization artefacts from Teflon filters are likely to be substantial at most locations in India, where temperatures exceed 30 °C for most of the year, and should be accounted for in assessments of gravimetrically determined PM2.5 mass closure using chemical species measured on multiple filter substrates.

How to cite: Bhardwaj, A. and Sunder Raman, R.: Estimation of organic positive artefacts on Quartz filters and volatilization loss from Teflon filters at a COALESCE network site - Bhopal, India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-196, https://doi.org/10.5194/egusphere-egu22-196, 2022.

Preben Van Overmeiren et al.

Antarctica is considered the most pristine environment on Earth. However, a detailed understanding of present-day atmospheric transport pathways of particles and volatile organic compounds (VOC) from source to deposition in Antarctica and the atmospheric reactions they undergo is essential to document biogeochemical cycles. Atmospheric composition plays an important role in present and near-future climate change. Airborne particles can serve as cloud condensation and ice nuclei and have therefore a strong influence on cloud formation and thus also on precipitation. This is of interest in Antarctica, since precipitation is the only source of mass gain to the Antarctic ice sheet which is expected to become the dominant contributor to global sea level rise in the 21st century. VOCs and their atmospheric oxidation products, secondary organic aerosols (SOA’s) can play an important role in this cloud formation process. However, current knowledge on VOCs and on the interaction between clouds, precipitation and aerosols in the Antarctic is still limited, both from direct observations and from regional climate models.

VOCs are traditionally sampled using axial thermal desorption sampling tubes containing a sorbent such as Tenax TA in a passive or active (pumped) fashion. While with passive sampling it is possible to sample over longer periods of time, up to a year in clean air conditions, the temporal information is lost. Because of uncertainties on the sample rate, which is driven by diffusion, obtaining precise air concentrations with passive sampling can be difficult. To sample VOC’s and oxidations products unsupervised and in a remote environment such as Antarctica a new active sequential sorbent tube autosampler was developed and deployed at the atmospheric observatory of the Princess Elisabeth Antarctic research station (71.95° S, 23.35° E, 1390 m asl). The autosampler collected samples from December 2019 to October 2020 and from January 2021 to June 2021. The obtained data is also used to complement and interpret atmospheric aerosol in-situ measurements conducted at the same location. Furthermore, to identify potential source regions, backward trajectory and dispersion modelling using FLEXTRA and FLEXPART will be applied. 

How to cite: Van Overmeiren, P., Delcloo, A., De Causmaecker, K., Mangold, A., Demeestere, K., Van Langenhove, H., and Walgraeve, C.: Sequential sampling of Volatile Organic Compounds (VOCs) and atmospheric oxidation products in the Sør Rondane Mountains, East-Antarctica., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12072, https://doi.org/10.5194/egusphere-egu22-12072, 2022.

Rachel O'Brien et al.

Brown carbon (BrC) in aerosol particles and cloud droplets can contribute to climate warming by absorbing solar radiation in the visible region of the solar spectrum. Large uncertainties remain in our parameterization of this warming, in part due to a lack of knowledge about atmospheric lifetimes for the chromophores (the light absorbing structures in BrC molecules). An important removal pathway includes chemical transformations that fragment the chromophore, thus removing its ability to absorb visible light. However, the photochemical loss rates measured in the laboratory do not generally match what is observed in ambient measurements. There are also different amounts of photo-resistant BrC, which is a fraction of the mixture that does not rapidly bleach. An important BrC source in the atmosphere is biomass burning and the overall photochemical decay rates for these emissions are important to quantify to improve our parameterizations of their radiative effects. Here we show results for laboratory studies of FIREX filter samples probing the role of water vapor in photolysis of aerosol particles irradiated on a filter. Kinetic analysis of photo-bleaching in aqueous solutions demonstrates that an intermediate photolysis rate should be included to improve predictions for BrC lifetimes in the atmosphere.

How to cite: O'Brien, R., Yu, H., Warren, N., Adamek, M., Jaffe, A., Lim, C., Kroll, J., Cappa, C., Jordan, C., and Anderson, B.: Photolysis of biomass burning organic aerosol, chemical transformations and photo-bleaching, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10504, https://doi.org/10.5194/egusphere-egu22-10504, 2022.

Sonia Afsana et al.

Organic aerosol (OA) is a ubiquitous component of atmospheric aerosol and affects radiative forcing not only by scattering but also by absorbing solar radiation. The light absorption property of OA should vary depending on its composition, which is not well understood to date. Humic-like substances (HULIS), a medium polar part of OA, constitute significant part of water-soluble organic matter (WSOM) and have light-absorbing capacity. In addition, recent studies showed that less polar water-insoluble organic matter (WISOM) absorbed light stronger than WSOM. Knowledge on the light absorption property of all the parts of OA in atmospheric aerosols is important to understand their contribution to aerosol light absorption. In this study, the light absorption property of extractable organics with low-to-high polarity in submicron aerosols collected at a forest site was characterized.

PM0.95 samples (particles with a diameter smaller than 0.95 mm) were collected on quartz filters in Tomakomai Experimental Forest of Hokkaido University, Japan, from June 2012 to May 2013. Organic aerosol components in the samples were extracted and fractionated by the combination of solvent extraction and solid-phase extraction methods. WSOM and WISOM were extracted sequentially by using multiple solvents. HULIS and highly-polar water-soluble organic matter (HP-WSOM) were fractionated from WSOM by solid-phase extraction. The light absorption by the OA fractions were measured using a UV-visible spectrometer. Further, a high-resolution time-of-flight aerosol mass spectrometer was used to quantify the OA fractions and to analyze the types of generated ions.

The mass absorption efficiency at 365 nm (MAE365) for WISOM was highest among all OA fractions (mean ± standard deviation: 0.37 ± 0.22 m2g-1), followed by the efficiencies for HULIS (0.14 ± 0.09 m2g-1) and HP-WSOM (0.07 ± 0.05 m2g-1). HULIS was shown to be whiter (more transparent) than that reported from previous studies. WISOM was the predominant light-absorbing OA fraction among three OA fractions. The absorption of solar radiation by the OA fractions relative to that by elemental carbon (f) was analyzed, and it showed an increase with the decrease of polarity: on average, the f values were 12%, 8%, and 2%, for WISOM, HULIS, and HP-WSOM, respectively, for the solar spectrum in a range from 300 to 500 nm. HULIS and WISOM showed noticeable seasonal changes in MAE365, which were higher in winter than in summer. Pearson’s correlation analyses between MAE365 and ion groups of OA fractions indicate that organic compounds with N, O, and S atoms may contribute substantially to the light absorption of OA components.

How to cite: Afsana, S., Zhou, R., Miyazaki, Y., Tachibana, E., Deshmukh, D. K., Kawamura, K., and Mochida, M.: Light absorption of forest organic aerosol fractions with different polarity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11354, https://doi.org/10.5194/egusphere-egu22-11354, 2022.

Max Coleman et al.

Radiative adjustments are additional contributions to instantaneous radiative forcing. They have the potential to strongly enhance the initial forcing, for example in the case of aerosol interactions with clouds. We investigate aerosol radiative adjustments in an Earth System model using an offline partial radiative perturbation (PRP) technique.

Radiative adjustments occur via many mechanisms. To understand them requires a variety of modelling techniques to separate individual adjustments. In PRP radiatively important variables simulated by the online model are input to an offline radiative transfer code to calculate the radiative effects of their adjustments. We apply the PRP method to adjustments arising from anthropogenic sulphate and black carbon industrial-era emission perturbations simulated by the UK Earth System Model 1 (UKESM1) using its offline radiative transfer code (SOCRATES) with settings closely matching the online simulations.

This method reduces errors introduced when using PRP with, or radiative kernels generated from, different settings or radiative transfer models to that used in the online climate model. We assess radiative adjustments arising from several factors, including cloud fields, and compare with their adjustments in the online simulations.

How to cite: Coleman, M., Collins, W., Shine, K., Bellouin, N., and O'Connor, F.: Determining aerosol radiative adjustments from UKESM1 with Partial Radiative Perturbation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10485, https://doi.org/10.5194/egusphere-egu22-10485, 2022.

Nora Fahrenbach and Massimo Bollasina

Many nations declared national lockdowns to limit the spread of COVID-19. This resulted in a dramatic, albeit temporary, reduction of many aerosol precursors and greenhouse gas emissions mainly from transport and industry. We analyse the output of various Earth system models participating in CovidMIP to investigate the impact of COVID-related emission reductions on the near-term climate across the Northern Hemisphere. A key finding is that surface anomalies are associated with a hemispheric-wide upper-tropospheric circulation response, featuring a wave-like pattern in the mid-latitudes and Arctic oscillation-type anomalies in the high latitudes during winter and spring. This is accompanied by changes in the vertical atmospheric temperature structure and consequent meridional shift of the NH jet. These anomalous patterns reverse between 2020 and 2021 and are shown to be consistent with the underlying changes in aerosol emissions. Our findings provide additional evidence to the important role of atmospheric circulation adjustments in realising the aerosol impact, which has significant implications for diagnosing the interplay between anthropogenic forcing and internal variability in the context of climate change.  

How to cite: Fahrenbach, N. and Bollasina, M.: Climate response to COVID-19 emission reductions: A testbed to understand atmospheric circulation adjustments to aerosol forcing , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-119, https://doi.org/10.5194/egusphere-egu22-119, 2022.

Mon, 23 May, 10:20–11:50

Chairpersons: Catherine Scott, Paul Griffiths, James Keeble

Stephanie Fiedler and Dian Putrasahan

The spatial distribution of anthropogenic aerosols was substantially different in the 1970s and 2000s. In the 1970s, a maximum in anthropogenic aerosol optical depth (τa) was situated over the North Atlantic, North America, and Europe. By the 2000s, the τa maximum has shifted to East Asia. That difference in the global pattern of τhas implications for the regional radiative effects and the regional climate. Here, we show how the differences in the global pattern of τa favour changes in the North Atlantic sea-surface temperature (NASST). To this end, we perform several hundred years of fully coupled atmosphere-ocean simulations with the CMIP6 model MPI-ESM1.2. Our simulations use observationally informed anthropogenic aerosol optical properties and a prescribed effect on the cloud albedo. All our simulations are sufficiently long to eliminate the impact of model-internal variability on the results.

Contrasting the output of the simulation using τa of the 1970s against the output from the pre-industrial control without τa largely shows the expected decrease in NASSTs, which is due to the surface cooling by the aerosol effects on radiation and clouds. Surprisingly, we also see an unusual warming response in the eastern sub-polar gyre - the same region that became known as the North Atlantic Warming Hole (NAWH). The described NASST responses reversed as we go from the anthropogenic aerosols of the 1970s to the 2000s, namely a relative decrease of the NASST in the region of the NAWH and an increase away from it. Analysing the atmosphere and ocean dynamics in the model output reveals that these NASST responses are driven by changes in the circulation of the model. The signal in the NAWH is explained by the oceanic meridional heat convergence that is primarily attributed to the gyre heat transport and not the overturning circulation that is often in focus of research. Our diagnostics also show a latitudinal shift of the jet stream over the North Atlantic being closer to the equator in the 1970s than in the 2000s, which is consistent with the response of the sub-polar gyre via the coupling by the wind stress at the ocean surface. Our results imply that the regional reduction in anthropogenic aerosols over the North Atlantic between the 1970s and 2000s favoured (1) a stronger NAWH cooling signal, (2) a stronger Arctic amplification measured by the NASST, and (3) a latitudinal shift of the mean position of the jet stream. Sensitivity tests with the model indicate that more than two-thirds of these signals are associated with aerosol effects on clouds. It highlights the need to better constraint aerosol-cloud interactions for an assessment of circulation responses to changes in atmospheric composition. 



Fiedler, S., and  Putrasahan, D., 2021: How does the North Atlantic SST pattern respond to anthropogenic aerosols in the 1970s and 2000s? Geophysical Research Letters,  48, e2020GL092142. https://doi.org/10.1029/2020GL092142.

How to cite: Fiedler, S. and Putrasahan, D.: Response of atmosphere-ocean circulation to aerosol patterns of the 1970s and 2000s, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3088, https://doi.org/10.5194/egusphere-egu22-3088, 2022.

Camilla Weum Stjern et al.

There is a strong interplay between processes within the planetary boundary layer (PBL) and the number of aerosols within it. Stable weather conditions are conducive to less vertical mixing, a shallower PBL and stronger accumulation of pollutants near the surface. In some cases, this can contribute to episodes of severe haze, with serious health impacts. A change in PBL height, however, may also be driven by changes in anthropogenic emissions and their influence on the atmosphere. In this study, we perform idealized simulation with the earth system model CESM2-CAM6, to investigate the effect of various climate drivers (CO2, black carbon and sulfate) on turbulence, planetary boundary layer height, and ultimately near-surface pollution. We find that while emissions of all three climate drivers influence the number of severe air pollution episodes, only CO2 and black carbon emissions do so through an impact on turbulence and PBL height. While black carbon aerosols are known to cause atmospheric heating, increased boundary layer stability and reduced turbulence, we find CO2 to have a similar albeit opposite effect through surface warming. Our results clearly underline the importance of black carbon mitigation for reducing the most severe exposures to air pollution.

How to cite: Stjern, C. W., Hodnebrog, Ø., Myhre, G., and Pisso, I.: Aerosol-boundary layer feedbacks triggered by both greenhouse gas and aerosol emissions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4264, https://doi.org/10.5194/egusphere-egu22-4264, 2022.

Ulas Im et al.

Fully coupled equilibrium simulations have been performed using the NASA Goddard Institute of Space Sciences (GISS) Earth system model (GISS-E2.1.2), where the East Asian and European land-based anthropogenic organic carbon (OC) emissions have been perturbed by five and seven times, respectively. GISS-E2.1.2 has been driven by the Coupled Model Intercomparison Project Phase 6 (CMIP6) anthropogenic emissions. GISS-E2.1.2 simulations have been performed using both the one moment aerosol (OMA) and the Multiconfiguration Aerosol TRacker of mIXing state (MATRIX) aerosol models, respectively, to quantify the impact of aerosol optical properties and the mixing state assumptions, i.e., external mixing in OMA vs internal mixing in MATRIX. 70 years of baseline and perturbation simulations have been performed for the year 2000 using a 5-member ensemble, where the last 30 years of simulations have been used for analyses.

In the present study, we will present the impact of the aerosol optical properties and mixing state on the OC and black carbon (BC) burdens and lifetimes, as well as the Arctic surface temperature response to the East Asian and European OC emissions in the form of regional temperature potentials (RTP). The preliminary results showed the OMA model simulated a general decrease in the global surface temperatures in response to the East Asian OC emissions, with no statistically significant response over the Arctic, while the MATRIX model showed increases over the globe, including statistically significant increases over the Arctic. Overall, the Arctic RTP in response to the East Asian OC emissions are -0.02 K Tg-1 and +0.00003 K Tg-1 using the OMA and MATRIX aerosol models, respectively.

How to cite: Im, U., Tsigaridis, K., Ekman, A. M. L., and Hansson, H.-C.: Arctic temperature responses to East Asian and European anthropogenic organic carbon emissions: impacts of externally vs internally mixed aerosols, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3778, https://doi.org/10.5194/egusphere-egu22-3778, 2022.

Rupert Holzinger et al.

During the PAMARCMiP 2018 campaign (March and April 2018) a proton-transfer-reaction mass spectrometer (PTR-MS) was deployed onboard the POLAR 5 research aircraft and sampled the High Arctic atmosphere under Arctic haze conditions. More than 100 compounds exhibited levels above 1 pmol/mol in at least 25% of the measurements. We used back trajectories and acetone mixing ratios to identify periods with and without long-range transport from continental sources.

Air masses with continental influence contained elevated levels of compounds associated with (aged) biogenic emissions or aged anthropogenic pollution (e.g., methanol, peroxyacetylnitrate (PAN), acetone, acetic acid, methylethylketone (MEK), proprionic acid, and pentanone), but benzene – a marker for primary pollution – was not enhanced. Almost half of all positively detected compounds (>100) in the High Arctic atmosphere can be associated with terpene oxidation products. This constitutes a strong signature of biogenic terpenes and their oxidation products on the High Arctic atmosphere. Many of these compounds will condense and produce biogenic secondary organic aerosol (SOA) – a natural source of organic aerosol (OA) in addition to the aerosols that can be associated with anthropogenic pollution. Therefore, we hypothesize that biogenic SOA exerted significant control over the complex system of aerosols, clouds and longwave radiation in the pre-industrial Arctic winter, even though their role is likely marginal under contemporary polluted Arctic haze conditions. However, biogenic SOA may become an important factor in the future again, if biogenic emissions are enhanced due to climate change and if polluting technologies are (hopefully) phased out in the near future.

During two flights, surface ozone depletion events (ODE) were observed that coincided with enhanced levels of acetone, and methylethylketone. There is evidence that ODEs may also be associated with the emission of biogenic ice-nucleating particles (INP) because the filter samples taken during these two flights exhibited enhanced levels of highly active ice-nucleating particles (INP).

Both these processes, INP production in association with ozone depletion events, and the transport of biogenic SOA could require corrections in estimates of preindustrial radiative forcing (RF). If preindustrial RF has been stronger, the Arctic amplification would be even stronger than currently assumed.

How to cite: Holzinger, R., Eppers, O., Adachi, K., Bozem, H., Hartmann, M., Herber, A., Koike, M., Millet, D., Ohata, S., and Stratmann, F.: Possible controls on Arctic clouds by natural aerosols from  long-range transport of biogenic emissions and ozone depletion events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12212, https://doi.org/10.5194/egusphere-egu22-12212, 2022.

Seohee Yang et al.

 Secondary organic aerosol (SOA) is produced through photochemical reactions between volatile organic compounds and oxidants in the atmosphere. SOA may have a strong climatic effect because it contains not only colorless carbon, which merely scatters light, but also colored carbon, which can absorb light. However, the climatic effect of SOA is still unclear because the coupled climate−atmospheric chemistry model has limitations in SOA simulation owing to the chemical complexity and high computing power consumption. Therefore, it is necessary to examine the long-term climate effects of SOA through a sophisticated SOA scheme. In this study, we investigate the effect of SOA on climate in East Asia using a long-term simulation by coupling the SOA scheme in the climate−atmospheric chemistry model. We developed an SOA module for the climate model that minimizes chemical processes and computing power consumption through parameterization using empirical parameters. The simulated SOA suitably captured the observed SOA, indicating that the SOA scheme is successfully coupled in the climate−atmospheric chemistry model. We conducted a control and two sensitivity simulations with four ensemble simulations for 19802020 to investigate the effect of whole radiative and only absorptive forcing of SOA on climate in East Asia. Climate change in the control simulation for 19802020 is much closer to reanalysis data than sensitivity simulation, implying a large contribution of SOA on East Asian climate in recent decades. Sensitivity simulation suggests that the light absorption of SOA affects the East Asian climate, causing an increase in temperature at the surface and a decrease in atmospheric stability. Considering that the simulated SOA concentration shows a noticeable increasing trend in East Asia over recent decades, our results imply that SOA has had a significant impact on long-term climate change over East Asia. Therefore, SOA simulation should be included in climate simulations in East Asia.

How to cite: Yang, S., Park, R., Lee, S., Jo, D., and Kim, M.: Impact of secondary organic aerosol on climate over East Asia for 1980–2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3455, https://doi.org/10.5194/egusphere-egu22-3455, 2022.

Tero Mielonen et al.

Biogenic secondary organic aerosol (BSOA) constitutes a major fraction of aerosol over boreal forests. As the emissions of BSOA precursors are temperature dependent, changes in temperature are likely to have substantial implications on regional aerosol radiative forcing. In this work, we have used a century long aerosol-climate model simulation to investigate the effect of increasing temperature on organic aerosol mass loadings, and further on aerosol-cloud interaction. The analysis was based on a nudged simulation done with ECHAM6-SALSA covering the period from 1905 to 2010. We limited the analysis to summer months to isolate the temperature dependence of biogenic emissions from the seasonal cycle of vegetation growth. We concentrated on three regions in Russia and three in Canada to analyze the spatial variability of the climatic impacts of BSOA. Our analysis showed that BSOA loadings increased with surface temperature and higher BSOA loads were connected to higher cloud condensation nuclei concentrations in all the regions. However, the relationship between BSOA and cloud optical thickness or cloud droplet size was not that clear in all the regions. These regional differences highlight the need to have accurate aerosol and cloud observations from various locations in the boreal region in order to estimate the climatic significance of biogenic aerosols.

How to cite: Mielonen, T., Tonttila, J., Romakkaniemi, S., Kühn, T., and Kokkola, H.: Simulation of Biogenic Aerosols in the Boreal Region and their Climatic Impact, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6286, https://doi.org/10.5194/egusphere-egu22-6286, 2022.

James Weber et al.

Emissions of volatile organic compounds from vegetation (BVOCs) affect climate via changes to O3, CH4, aerosol and clouds. BVOC emissions themselves exhibit dependencies on climate (causing a feedback) and land use change including certain climate change mitigation strategies. Therefore, emissions are predicted to change under future climate pathways yet there remains considerable uncertainty between climate models in the sign and magnitude of the net climatic impact BVOCs (Thornhill et al., 2021). 

One contributor is uncertainty in the description of BVOC chemistry, hitherto minimally assessed in a climate context despite recent scientific advances. In the climate model UKESM1 we evaluate the influence of chemistry by comparing the response to a doubling of BVOC emissions in a pre-industrial (PI) atmosphere using standard and state-of-the-art chemistry mechanisms, the latter featuring recent improvements in chemical understanding. The feedback is positive in both mechanisms with the negative feedback from enhanced aerosol scattering outweighed by positive feedbacks from O3 and CH4 increases and aerosol-cloud interactions (ACI). We suggest the ACI response, contrary to past studies, is probably driven by reductions in cloud droplet number concentration (CDNC) via suppression of gas phase SO2 oxidation. 

The net feedback is 43% smaller with state-of-the-art chemistry due to lower oxidant depletion which yields smaller increases in CH4 and smaller decreases in CDNC. Thus, the PI climate in UKESM1 is only about half as sensitive to a change in BVOC emissions with state-of-the-art chemistry, highlighting the important influence of simulated chemistry.  

The role of chemistry is also compared to the inter-model variation in BVOC forcing. We suggest the variation in chemistry between models is likely to play a large role in explaining the variation in the BVOC feedback from O3 and CH4 changes and a smaller role in the aerosol feedback, highlighting the need to improve the descriptions of BVOC chemistry and BVOC-aerosol coupling in tandem to improve assessments of the climatic impact of future BVOC emission changes.



How to cite: Weber, J., Archer-Nicholls, S., Abraham, N. L., Shin, Y. M., Griffiths, P., Grosvenor, D. P., Scott, C. E., and Archibald, A. T.: Climate feedback from vegetation emissions strongly dependent on modelling of atmospheric chemistry., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6446, https://doi.org/10.5194/egusphere-egu22-6446, 2022.

Flossie Brown et al.

Climate change has the potential to increase surface ozone concentrations, known as the ‘ozone-climate penalty’, through changes to atmospheric chemistry, transport and land surface behaviour. In the tropics, the response of surface ozone to a changing climate is relatively understudied, but will have important consequences for air pollution, human and ecosystem health. In this study, we predict the change in surface ozone due to climate change over South America and Africa using data from 3 state-of-the-art Earth system models from CMIP6. To identify the changes driven by climate change alone, we use the difference between the Shared Socioeconomic Pathway 3 7.0 emissions scenario which includes climate change and the same scenario without climate change. The SSP3 7.0 scenario has high emissions of near-term climate forcers and substantial land-use change leading to large temperature changes.

We find that by 2100, there will be an ozone-climate penalty in areas where background ozone is already high, namely urban and biomass burning areas. This includes robust annual mean increases in surface ozone of up to 4 ppb over polluted regions such as the arc of deforestation in the Amazon, with dry season months showing increases of up to 15 ppb. These areas have high NOx emissions from fires, transport or industry. However, models disagree on the role of climate change in remote, low-NOx regions, partly because of uncertainties in NOx concentrations. We also find that the magnitude and location of the ozone-climate penalty in the Congo basin has greater inter-model variation than the Amazon.

We attribute the increase in surface ozone concentration to an increase in the rate of ozone chemical production, which is strongly influenced by the background NOx concentration. As NOx emissions are largely anthropogenic, this suggests that without reduction in emissions, forested areas in urban and agricultural locations are at increasing risk of ozone damage due to climate change. This has implications for the success of secondary forests and other human-modified forests which are mostly located in agricultural areas, deforestation frontiers and forest edges.

How to cite: Brown, F., Sitch, S., and Folberth, G.: The ozone-climate penalty over South America and Africa by 2100, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7352, https://doi.org/10.5194/egusphere-egu22-7352, 2022.

Prodromos Zanis et al.

It is presented an analysis of the effect of climate change on surface ozone (O3) discussing the related penalties and benefits around the globe from the global modeling perspective based on simulations with five CMIP6 (Coupled Model Intercomparison Project Phase 6) Earth System Models. All models conducted simulation experiments considering future climate (ssp370SST) and present-day climate (ssp370pdSST) under the same future emissions scenario (SSP3-7.0). Over regions remote from pollution sources, there is a robust decline in mean surface ozone concentration varying spatially from -0.2 to -2 ppbv oC-1, with strongest decline over tropical oceanic regions, which is mainly linked to the dominating role of enhanced ozone chemical loss with higher water vapour abudances under a warmer climate. However, ozone increases over regions close to anthropogenic pollution sources or close to enhanced natural Biogenic Volatile Organic Compounds (BVOC) emission sources with a rate ranging regionally from 0.2 to 2 ppbv oC-1, implying a regional surface ozone penalty due to global warming. The individual models show this robustly for south-eastern China and India as well as for regions of Africa but there are inter-model differences in areas within Europe and the United States (US) as well as in South America. The future climate change enhances the efficiency of precursor emissions to generate surface ozone in polluted regions and thus the magnitude of this effect depends on the regional emission changes considered in this study within the SSP3_7.0 scenario. The comparison of the climate change impact effect on surface ozone versus the combined effect of climate and emission changes indicates the dominant role of precursor emission changes in projecting surface ozone concentrations under future climate change scenarios.


The authors from Aristotle University of Thessaloniki acknowledge funding from the Action titled "National Νetwork on Climate Change and its Impacts - CLIMPACT" which is implemented under the sub-project 3 of the project "Infrastructure of national research networks in the fields of Precision Medicine, Quantum Technology and Climate Change", funded by the Public Investment Program of Greece, General Secretary of Research and Technology/Ministry of Development and Investments.

How to cite: Zanis, P., Akritidis, D., Turnock, S., Naik, V., Szopa, S., Georgoulias, A. Κ., Bauer, S. E., Deushi, M., Horowitz, L. W., Keeble, J., Le Sager, P., O'Connor, F. M., Oshima, N., Tsigaridis, K., and van Noije, T.: Climate change impact on surface ozone based on CMIP6 Earth System Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12257, https://doi.org/10.5194/egusphere-egu22-12257, 2022.

Alvaro Patricio Prieto Perez et al.

Extreme air pollution in European cities, especially those in central and eastern Europe is, regardless of strict pollution control measures, still present, representing a large health burden on their inhabitants. Understanding the processes that control or modulate such events over urban areas is therefore crucial. In general, the climate-chemistry interactions over urban areas are complex with multiple feedbacks. In this study, based on two air pollution events with i) high winter PM concentrations and stagnant conditions (14 days in January 2017), ii) elevated ozone levels during a dry sunny summer period (14 days in August 2015), we will examine the mutual role of urban emissions (and secondary pollutants formed from them) and the urban canopy meteorological forcing (UCMF) over central Europe. We performed a series of WRF-Chem simulations with/without urban land-surface (effect of rural-urban transition) and with/without urban emissions, while six large central European cities were considered. Impact on both meteorological conditions and chemical species is examined.

Regarding the impact on meteorological conditions (temperature, windspeed, boundary layer height), we showed that the direct effect of UCMF (1-2K for temperature) is much larger than the secondary effects of the radiative impacts of urban emissions (driven mainly by aerosol effects; 0.1 K for temperature in average). It was also shown that these radiative impacts depend whether UCMF is included or not, with differences up to 2 K in hourly values. The impact on chemical concentrations is driven especially by UCMF causing decrease of PM and increase of ozone while the indirect effects of urban emissions induced meteorological changes are substantially smaller.


How to cite: Prieto Perez, A. P., Huszar, P., and Karlicky, J.: Extreme PM and ozone pollution over central Europe: interactions of the urban canopy meteorological forcing and radiative effects of urban emissions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2154, https://doi.org/10.5194/egusphere-egu22-2154, 2022.

Antoine Guion et al.

Tropospheric ozone (O3) plays a critical role in maintaining the oxidative capacity of the troposphere. However, as a high oxidant, it also deteriorates air quality at high concentration, inducing adverse effects on human and ecosystem health. Meteorological conditions are key to understand the variability of many surface atmospheric pollutants and of the vegetation state. The variability of O3 concentration is generally well represented in chemistry-transport models (CTM) compared to observations, but the amplitude of the variations are more difficult to simulate (peaks and minima). One factor that has been identified as a possible cause of these uncertainties is the lack of interactions between the biosphere and the atmosphere.

The aim of this study is to quantify the variation of surface O3 over the Southwestern Europe during agricultural droughts, combined or not with heatwaves. Therefore, we analyze both emissions of biogenic volatile organic compounds (BVOCs) and O3 dry deposition velocity during these extreme events, based on the available observations (O3 from the EEA surface network and formaldehyde (HCHO) from OMI satellite instrument) and regional CTM simulations (CHIMERE model), which have been clustered depending on the underlying meteorological conditions. To better understand the observed variations, sensitivity studies are performed implementing the effect of soil dryness and biomass decrease in CHIMERE CTM simulations using online calculation of BVOC emissions from the MEGAN model, during three selected summers: 2012, 2013 and 2014.

Our results show that observed O3 concentration is on average significantly higher during heatwaves (+10µg/m3 in daily mean and +18µg/m3 in daily maximum) and droughts (+5µg/m3 and +9µg/m3), due to an overall O3 precursor emissions enhancement (in agreement with HCHO observations) and O3 dry deposition decrease. However, isolated droughts are characterized by reduced O3 precursor emissions (in agreement with HCHO observations) and reduced O3 dry deposition, compared to normal conditions. Both effects compensate each other with a slight dominance of the latter one, leading to a small but significant increase of observed O3 concentration for the daily maximum only (+4 μg/m3). However, important uncertainties appear to be related to BVOC concentrations, especially about the land cover classification, and to NOX concentrations for which CHIMERE presents limited performance scores of validation. Nevertheless, we emphasize the need for a more dynamical interaction between surface vegetation and hydrology, meteorology and atmospheric chemistry for the simulation of O3 during summers in Southwestern Europe.

Finally, almost half of summer days exceeding the EU standard of O3 for air quality in Southwestern Europe occurred during droughts or heatwaves, on average for the time period 2000-2016. However, this percentage can increase (up to 80%) for exceptionally dry and hot summers, like in 2012. Only 14% of the exceedance days occurred during isolated droughts (summers 2000-2016).

How to cite: Guion, A., Turquety, S., Cholakian, A., Polcher, J., Ehret, A., and Lathière, J.: Impact of droughts and heatwaves on surface ozone over Southwestern Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9271, https://doi.org/10.5194/egusphere-egu22-9271, 2022.

Mon, 23 May, 13:20–14:50

Chairpersons: William Collins, Catherine Scott, Christopher Smith

Catherine Hardacre et al.

UKESM1.1 is the latest generation Earth system model to be developed in the UK. It simulates the core physical and dynamical processes of land, atmosphere, ocean and sea ice systems which are extended to incorporate key marine and terrestrial biogeochemical cycles. These include the carbon and nitrogen cycles and interactive stratosphere-troposphere trace gas chemistry. Feedbacks between these components that have an important amplifying or dampening effect on the physical climate, and/or change themselves in response to changes in the physical climate are also included. One focus for the development of UKESM1.1 is to include a representation of nitrate aerosol chemistry in the aerosol-chemistry scheme, UKCA-Mode. Nitrate aerosol is a major aerosol component and contributes to air pollution episodes, ecosystem destruction, regional haze, and aerosol-induced climate forcing. In addition, the emission, chemical transformation and deposition processes for nitrate aerosol span land-atmosphere boundaries and can impact feedbacks between these systems. 

A new nitrate aerosol scheme has recently been developed for, and evaluated in, UKCA-Mode. We have successfully implemented this new scheme into the atmosphere only configuration of UKESM1.1 and explored its impact on aerosol, aerosol-cloud interactions and radiative forcing at the global scale. UKESM1.1-nitrate simulates the largest nitrate sources over China, India, Europe, eastern USA and central Africa, and we see corresponding increases in aerosol optical depth (AOD) of up to 30% over these regions. The addition of nitrate aerosol also drives increases in cloud droplet number concentration (CDNC) and reduces the net downward radiation at the top of atmosphere by 0.4 W m-2. The latter is primarily driven by decreases in the outgoing short-wave radiation at the top of atmosphere. Evaluation of simulated nitrate aerosol against observations surface concentrations and AOD from AERONET suggest that while UKESM1.1 captures the spatial distribution of nitrate aerosol, the model may be over-predicting it’s atmospheric loading and consequently impacts on radiative forcing may also be over-predicted. 

The inclusion of nitrate aerosol chemistry in UKESM1.1 is a step-change in the model’s aerosol modelling capability. We will further investigate the role of nitrate aerosol in the Earth system by calculating its contribution to the aerosol effective radiative forcing and through development of the scheme in the fully coupled UKESM1.1 configuration. 

How to cite: Hardacre, C., Mulcahy, J., Jones, A., and Jones, C.: Nitrate aerosol chemistry in UKESM1.1: impacts on composition and climate , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7666, https://doi.org/10.5194/egusphere-egu22-7666, 2022.

Fiona O'Connor et al.

Despite methane’s importance as a greenhouse gas, the Earth System Models that contributed to Phase 6 of the Coupled Model Intercomparison Project (CMIP6) typically prescribe surface methane concentrations - following either historical observations or specified future shared socioeconomic pathways. Here, we make use of a methane emissions-driven configuration of the UK’s Earth System Model to explore the role of an interactive methane cycle, including a wetlands emissions scheme, on the model’s equilibrium climate sensitivity and its transient climate response to changes in carbon dioxide concentration. In addition, climate-driven feedbacks play a fundamental role in determining the climate response to external forcings and this work will investigate the impact of interactive methane on the assessment of relevant Earth System feedbacks.

This presentation will demonstrate the need for including interactive methane in Earth System Models, thereby enabling decision makers to determine the consequences of methane emission reduction policies or climate feedbacks on natural methane sources towards meeting global climate as well as global air quality targets.

How to cite: O'Connor, F., Folberth, G., Gedney, N., and Jones, C.: The role of an interactive methane cycle in the Earth System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4186, https://doi.org/10.5194/egusphere-egu22-4186, 2022.

Man Mei Chim et al.

Large explosive volcanic eruptions can induce global climate impacts on decadal to multi-decadal timescales. In current climate models, future volcanic eruptions are represented in terms of a time-averaged volcanic forcing that ignores the sporadic nature of volcanic eruptions. This conventional representation does not account for how climate change might affect the dynamics of volcanic plumes and the stratospheric sulfate aerosol lifecycle and, ultimately, volcanic radiative forcing. To account for these climate-volcano feedbacks in climate projections, we perform model simulations from 2015 to 2100 with two key innovations: (1) a stochastic resampling approach to generate realistic future eruption scenarios based on historical volcanic eruptions recorded by ice cores and satellites in the past 11,500 years; and (2) a new modelling framework, UKESM-VPLUME, which couples a 1-D eruptive plume model (Plumeria) with an Earth System Model (UKESM) to consider the impacts of changing atmospheric conditions on eruptive plume heights. Our results show that considering sporadic small-magnitude volcanic eruptions in a future warming scenario can lead to a noticeable difference in global surface temperatures as well as on the time at which temperatures exceed 1.5°C above pre-industrial levels. Our study highlights the importance of considering sporadic eruptions and the changes in eruptive plume heights in a future warmer climate.  The UKESM-VPLUME model framework enables us to quantify the impacts of climate change on volcanic radiative forcing in an Earth System model, which in future research allows us to better evaluate the climate impacts of volcanic eruptions under global warming.

How to cite: Chim, M. M., Aubry, T. J., Abraham, L. N., and Schmidt, A.: Examining the climate impacts of future volcanic eruptions , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2749, https://doi.org/10.5194/egusphere-egu22-2749, 2022.

Anna Novelli et al.

The oxidation of carbonyl sulfide (OCS) is the primary, continuous source of stratospheric sulfate aerosol particles, which can scatter shortwave radiation and catalyze heterogeneous reactions in the stratosphere. While it has been estimated that the oxidation of dimethyl sulfide (DMS), emitted from the surface ocean, accounts for 8-20% of the global OCS source, there is no existing DMS oxidation mechanism relevant to the marine atmosphere that is consistent with an OCS source of this magnitude. We describe new laboratory measurements and theoretical analyses of DMS oxidation that provide a mechanistic description for OCS production from hydroperoxymethyl thioformate (HPMTF), an ubiquitous, soluble DMS oxidation product.

The mechanism for OCS formation from DMS + OH is found to proceed through several intermediate stages, including secondary OH-initiated oxidation of hydroperoxymethyl thioformate (HOOCH2SCH=O), thioperformic anhydride (O=CHSCH=O), and thioperformic acid (HOOCH=S and HOSCH=O). Several of these reactions are affected by chemical activation, leading to prompt product formation. A theoretical kinetic analysis of these reactions and of conditions representative of the marine boundary layer shows several potential OCS formation channels, which combined lead to a high yield of OCS under OH-initiated oxidation of DMS.

We incorporate this chemical mechanism into a global chemical transport model, showing that OCS production from DMS is a factor of 3 smaller than current estimates and displays a maximum in the tropics consistent with field observations. A critical factor in the conversion of DMS to OCS is the heterogeneous loss of the soluble intermediates, making the OCS yield sensitive to multiphase cloud chemistry and reducing the total OCS formation.

How to cite: Novelli, A., Jernigan, C., Fite, C., Vereecken, L., Berkelhammer, M., Rollins, A., Rickly, P., Taraborelli, D., Holmes, C., and Bertram, T.: Efficient production of carbonyl sulfide in the low-NOx oxidation of dimethyl sulfide, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10194, https://doi.org/10.5194/egusphere-egu22-10194, 2022.

Marina Friedel et al.

In the Arctic, the timing of the Final Stratospheric Warming (FW), which marks the transition from winter to summer, is subject to a large interannual variability. Early and late FWs have previously been linked to different mechanism and are associated with different surface responses. While early FWs are predominantly wave driven and followed by a negative Arctic Oscillation (AO) at the surface, late FWs are more radiatively driven and not linked to a specific surface pattern. Simultaneously, the time around the vortex weakening in spring is marked by large year-to-year variations in stratospheric ozone concentrations which both respond and feed back into dynamics. A causal connection between stratospheric ozone anomalies and the FW date via ozone-dynamic feedbacks is thus plausible, but still largely unstudied.


We investigate the relationship between springtime ozone anomalies and the FW date at both 10 and 50 hPa in Chemistry Climate model simulations with fully interactive and prescribed climatological ozone. For years with low springtime ozone concentrations, we find that the FW at 50 hPa is significantly delayed by 1-2 weeks and is not followed by surface anomalies. In contrast, in years with high springtime ozone concentrations, the 50 hPa FW happens 1-2 weeks earlier than average and precedes a negative AO pattern at the surface. Most importantly, the connection between springtime ozone concentrations and 50 hPa FW date is only present in model simulations where ozone anomalies are radiatively active. In addition, surface patterns after early FWs are enhanced when interactive ozone is included in the simulations. No clear relationship between stratospheric ozone anomalies and 10 hPa FW date is found


We identify additional radiative heating/cooling due to high/low ozone anomalies as the main mechanism whereby ozone feedbacks affect the FW date and discuss subsequent impacts on wave dissipation. Following our results, stratospheric ozone anomalies contribute to the occurrence of late and early FWs in spring and significantly enhance surface impacts of early FWs, which emphasizes the importance of interactive ozone chemistry for subseasonal to seasonal predictions.

How to cite: Friedel, M., Chiodo, G., Stenke, A., Domeisen, D., and Peter, T.: The influence of ozone feedbacks on Final Stratospheric Warmings and their surface impact, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12061, https://doi.org/10.5194/egusphere-egu22-12061, 2022.

Paul Griffiths et al.

A grand challenge in the field of chemistry-climate modelling is to understand the connection between anthropogenic emissions, atmospheric composition and the radiative forcing of trace gases and aerosols. 

We present an analysis of the trends in tropospheric oxidising capacity in the UM-UKCA from the recent forerunner to AerChemMIP, the Chemistry-Climate Model Intercomparison project, CCMI-1, focusing on the REFC1SD and REFC1 simulations over the recent historical period.  We discuss these trends in terms of OH preconditions, such as photolysis rate and ozone concentration, and the resulting impact on methane oxidation.

Observational data provide important constraints on ozone and its precursors, as well as other radiatively important gases such as methane.  Data are available from a variety of platforms, spanning a range of spatial and temporal scales covering the past 40 years.   Recent work has highlighted the discrepancy in model and observations concerning surface ozone at key stations and the trend in tropospheric ozone levels over the past 50 years.

We will present a comparison between modelled OH and recent observational products, such as flight data from the UK ACSIS  and NASA AToM campaigns to examine how such data may be used to assess and to validate chemistry-climate models such as UKCA, and so improve the uncertainty regarding key forcing agents such as methane, ozone and aerosols. 

How to cite: Griffiths, P., Keeble, J., Hickman, S., Shin, Y. M., Abraham, N. L., Pyle, J., and Archibald, A.: Studies of the effect of stratospheric ozone depletion on tropospheric oxidising capacity over the period 1979-2010 using the UKCA Chemistry-Climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3754, https://doi.org/10.5194/egusphere-egu22-3754, 2022.

James Keeble and Paul Griffiths

The transport of ozone from the stratosphere to the troposphere is a key contributor to the tropospheric ozone budget. It is estimated that the stratosphere-to-troposphere flux of ozone leads to ~500 Tg of ozone transported into the troposphere each year, which is comparable to the net chemical production of ozone within the troposphere. Using simulations performed with the UKESM1 Earth system model we explore how transport of ozone from the stratosphere to the troposphere has changed over the recent past, and explore the drivers of these changes. Additionally, we calculate the contribution of ozone with a stratospheric origin to tropospheric ozone radiative forcing, and explore the impacts of STE on regional air quality.

How to cite: Keeble, J. and Griffiths, P.: Role of Stratosphere-Troposphere Exchange of Ozone in the Earth System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12426, https://doi.org/10.5194/egusphere-egu22-12426, 2022.

Tianyi Fan et al.

Anthropogenic emission inventory for aerosols and reactive gases is crucial to the estimation of aerosol radiative
forcing and climate effects. Here, the anthropogenic emission inventory for AerChemMIP, endorsed by CMIP6, is briefly
introduced. The CMIP6 inventory is compared with a country-level inventory (i.e., MEIC) over China from 1986 to 2015.
Discrepancies are found in the yearly trends of the two inventories, especially after 2006. The yearly trends of the aerosol
burdens simulated by CESM2 using the two inventories follow their emission trends and deviate after the mid-2000s, while
the simulated aerosol optical depths (AODs) show similar trends. The difference between the simulated AODs is much
smaller than the difference between model and observation. Although the simulated AODs agree with the MODIS satellite
retrievals for country-wide average, the good agreement is an offset between the underestimation in eastern China and the
overestimation in western China. Low-biased precursor gas of SO2, overly strong convergence of the wind field, overly
strong dilution and transport by summer monsoon circulation, too much wet scavenging by precipitation, and overly weak
aerosol swelling due to low-biased relative humidity are suggested to be responsible for the underestimated AOD in eastern
China. This indicates that the influence of the emission inventory uncertainties on simulated aerosol properties can be
overwhelmed by model biases of meteorology and aerosol processes. It is necessary for climate models to perform
reasonably well in the dynamical, physical, and chemical processes that would influence aerosol simulations.

How to cite: Fan, T., Liu, X., Wu, C., Zhang, Q., Zhao, C., Yang, X., and Li, Y.: Comparison of the Anthropogenic Emission Inventory for CMIP6 Models with a Country-Level Inventory over China and the Simulations of the Aerosol Properties, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11195, https://doi.org/10.5194/egusphere-egu22-11195, 2022.

William Collins

Phase six of the Coupled Model Intercomparison Project (CMIP6) was the first CMIP to include significant numbers of climate models with interactive aerosols and chemistry. The AerChemMIP project was designed to understand the effects of interactive representation of aerosols and chemistry in model simulations of the past and future climate, and also to take advantage of this to further our fundamental understanding of aerosol and chemistry processes in the climate system.

The four science objectives of AerChemMIP were:

  • How have anthropogenic emissions contributed to global radiative forcing and affected regional climate over the historical period?
  • How might future policies (on climate, air quality and land use) affect the abundances of NTCFs and their climate impacts?
  • How do uncertainties in historical NTCF emissions affect radiative forcing estimates?
  • How important are climate feedbacks to natural NTCF emissions, atmospheric composition, and radiative effects?


The AerChemMIP project has already led to more than 15 published papers. These advanced our knowledge in: the evolution of aerosol and chemical processes over the historical period, the contributions of these species to past radiative forcing and climate and their effect on future climate, and the impacts of different scenarios for future atmospheric composition and air quality. These have all made significant contributions to the IPCC 6th Assessment Report. We show that including interactive aerosols and chemistry in climate models is crucial to simulating past and future climates, provided we understand the behaviour of the fundamental processes.

How to cite: Collins, W.: Aerosols and Chemistry in the CMIP6 models – new science from AerChemMIP, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10047, https://doi.org/10.5194/egusphere-egu22-10047, 2022.

Alexander Archibald et al.

 Over the past few decades the global atmospheric chemistry modelling community has collectively simulated 100000s of model years, producing petabytes of output, using increasingly complex  chemistry and aerosol schemes and higher resolution models. Yet, our understanding of key aspects of global atmospheric composition change has not evolved at the same pace as the tools we use to study it. Answers to key questions remain as uncertain now as they were two decades ago, including the strength of the methane self-feedback and the past and possible future evolution of tropospheric ozone in response to changing emissions and climate. Here, we will review the progress in understanding that has been generated in model intercomparison experiments (MIPs) from the last three IPCC assessment cycles: ACCENT (AR4), ACCMIP (AR5), and CCMI and AerChemMIP (AR6). We conclude that the aims and experimental design in these MIPs can be improved to reduce  the uncertainty in some of the outstanding questions in atmospheric chemistry. To this end  we propose a new set of experiments, specifically targeted at the atmospheric chemistry modelling community, that will go towards resolving outstanding challenges and integrate the wealth and expertise of chemistry transport and chemistry climate models. These experiments emulate the CMIP DeCK experiments and are designed to provide a continuing legacy for the community in understanding model evolution and process understanding. We aim to elicit  feedback and input into the experimental design from the community  with this presentation. 

How to cite: Archibald, A., Collins, W., Evans, M., Griffiths, P., O'Connor, F., Wild, O., and Young, P.: Ace in the hole or a house of cards: Will a DeCK experiment help atmospheric chemistry?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9442, https://doi.org/10.5194/egusphere-egu22-9442, 2022.