Natural Aerosols in Climate Change

A better understanding of the role of natural aerosols in the atmosphere is essential for assessing anthropogenic radiative forcing and the climate response. 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. Questions of particular interest are, but not limited to:

- How can we distinguish between truly natural aerosols and those whose emissions or formation are influenced by anthropogenic activities?
- Where are the missing links in our understanding of the lifecycle of natural aerosols?
- How does the contributions of natural aerosols to atmospheric composition and deposition change over time?
- What are the consequences of changes in natural aerosols, e.g., for photovoltaic power production?

Convener: Stephanie Fiedler | Co-conveners: Douglas Hamilton, Kerstin Schepanski, Catherine Scott
vPICO presentations
| Thu, 29 Apr, 13:30–14:15 (CEST)

vPICO presentations: Thu, 29 Apr

Chairpersons: Stephanie Fiedler, Catherine Scott
Tianle Yuan, Hongbin Yu, Mian Chin, Lorraine Remer, David McGee, and Amato Evan

African dust exhibits strong variability on a range of time scales. Here we show that the interhemispheric contrast in Atlantic SST (ICAS) drives African dust variability at decadal to millennial timescales, and the strong anthropogenic increase of the ICAS in the future will decrease African dust loading to a level never seen during the Holocene. We provide a physical framework to understand the relationship between the ICAS and African dust activity: positive ICAS anomalies push the Intertropical Convergence Zone (ITCZ) northward and decrease surface wind speed over African dust source regions, which reduces dust emission and transport. It provides a unified framework for and is consistent with relationships in the literature. We find strong observational and proxy‐record support for the ICAS‐ITCZ‐dust relationship during the past 160 and 17,000 years. Model‐projected anthropogenic increase of the ICAS will reduce African dust by as much as 60%, which has broad consequences. We posit that dust cannot be thought of as a purely natural phenomenon.

How to cite: Yuan, T., Yu, H., Chin, M., Remer, L., McGee, D., and Evan, A.: Anthropogenic Decline of African Dust inferred from Insights From the Holocene Records and Beyond: are dust purely  natural?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-262,, 2020.

Robert Scheele and Stephanie Fiedler

Renewable energy produced by photovoltaic (PV) power plants strongly depends on the meteorological conditions. Desert-dust aerosols impair the radiative transfer in the atmosphere, but their effect on PV power is poorly understood from a climatological perspective. Past climate model simulations are known to have a large spread in dust-aerosol loading. With the new CMIP6 model simulations now being available, we revisit the climate-model spread in representing desert-dust aerosols for 1985 to 2014, assess the dust-aerosol changes until 2100, and estimate the associated differences in the PV power potential. To this end, we evaluate the dust aerosol optical depth (DOD) in the CMIP6 historical simulations using modern reanalysis and satellite data. Our results highlight the persistent model spread for DOD in CMIP6, but a multi-model mean DOD close to the reanalysis and satellite data. We identify only slight changes in both the global and regional mean DOD in a green scenario (ssp126) at the end of the 21st century. For a future with continued strong warming (ssp245, ssp585), the simulations suggest an increase (decrease) in regional DOD associated with North-African, Transatlantic transport, and Australia (Taklamakan Desert) dust emissions. The differences in simulated DOD imply changes in the PV power potential for regions affected by dust aerosols. We compute the change in the PV power potential from surface irradiance, temperature, and wind speed in the CMIP6 scenarios against present-day. Our results point to a PV power potential for North Africa that is similarly affected by a future increase in temperature and decrease in irradiance associated with more dust aerosols. In mid-latitude regions of the northern hemisphere, a future change in PV power potential is controlled by changes of clouds and temperature. Our PV power estimates underline the impacts of the model uncertainty in DOD, the degree of future warming, and the unclear response of clouds and circulation to the warming.

How to cite: Scheele, R. and Fiedler, S.: Dust-aerosol optical depth in CMIP6 models and implication for PV-power generation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2049,, 2021.

Jean Sciare, Roland Sarda-Estève, Konstantina Oikonomou, Elie Bimenyimana, Michael Pikridas, Florin Unga, and Aliki Christodoulou

Major efforts are currently put to reduce drastically PM emissions at the exhaust of the most recent vehicles, however, little is done to mitigate non-tail-pipe emissions and resuspended road dust, in particular. Such traffic-related resuspension of dust may become a major source of PM10 at a time our cars are becoming cleaner. This may be particularly true in (semi-)arid urban environments which are characterized by high deposition rates of desert dust and low rain wash-out rates of roads.

Near-real-time (10-min time resolution) on-line measurement of selected cations (Na+, Mg2+, Ca2+) in PM10 were performed using a Particle-into-liquid-sampler (PILS) coupled with an Ion Chromatograph (IC). Such high temporal resolution of these species has been rarely reported in literature and to the best of our knowledge, it is the first time that such dense observations are reported in PM10 for urban environment. These measurements were performed during a 3-month transition period between (from wet winter to dry summer) at an urban background site of Nicosia (Cyprus) a central location of the Eastern Mediterranean Middle East (EMME) region.

The consistency of these measurements was successfully assessed against 24-h integrated filter-based measurements while hypotheses related to the use of Calcium as a tracer of dust particles further verified against trace metal analysis. A comprehensive suite of co-located ancillary data (Aethalometer, Lidar, ACSM, SMPS, OPC) were used to further support the daily/weekly/monthly variability of Calcium concentration in PM10.

Diurnal variability of dust concentration in PM10 at our background urban site displayed a strong and intense traffic-related source at rush hours together with a maximum observed in the afternoon in phase with the development of the Planetary Boundary Layer and intrusion of desert dust from aloft. Interestingly, this pattern is amplified when moving from wet to dry months and encompassing the Spring dust season.

The contribution of the two dust sources in PM10 (traffic-related dust resuspension and intrusion of long-range transported desert dust) is provided here for different temporal scales (day, week, month). Estimate of traffic-related (non-)tail-pipe emissions (ie. combustion carbonaceous vs resuspended dust) is also provided here highlighting the dominant role of dust in PM10 emissions from road transport sector.

How to cite: Sciare, J., Sarda-Estève, R., Oikonomou, K., Bimenyimana, E., Pikridas, M., Unga, F., and Christodoulou, A.: Real-time source apportionment of local vs regional dust in a semi-arid urban environment of the Eastern Mediterranean Middle East (EMME) region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14115,, 2021.

Marina Liaskoni, Lukas Bartik, and Peter Huszar

Windblown dust, emitted from the surface of the earth to the atmosphere as a result of the disintegration of material due to wind drag, can have a significant impact on the atmospheric concentration of PM, especially over (semi-)arid areas. They however may be important occasionally also over non-arid regions with considerable precipitation (e.g. over midlatitudes). Therefore their contribution to the total PM pollution cannot be neglected, especially considering the increasing potential of droughts in a changing climate, when long dry periods occur between precipitation events.

Here, we investigate the regional impact of PM emissions from wind erosion on urban PM levels for a central European domain using a well-established windblown dust module (called ‘‘WBDUST’’) for the 2018-2019 period. As driving meteorological data, we used WRF simulations. Before applying WBDUST, we made some modifications which ensured that the surface heterogeneity for vegetation cover is taken into account. This is important as for grid cells, where the average leaf-area-index (LAI) is higher than a certain threshold, zero emissions would be produced. However, if we take into account the fractional character of LAI, emissions will be more realistic. The obtained emission fluxes were comparable to anthropogenic ones indicating the great importance of windblown dust even over such non-arid areas. WBDUST emissions were implemented into the CAMx chemistry transport model and we performed simulations with and without these emissions. Our results showed that urban PM levels are significantly higher if wind-blown dust is considered and match better with observations.

How to cite: Liaskoni, M., Bartik, L., and Huszar, P.: Modeling the regional dust emissions in central Europe and their contribution to urban PM levels, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3863,, 2021.

Yusuf Bhatti, Laura Revell, Adrian McDonald, and Jonny Willaims

We studied sulfate aerosols over the Southern Ocean using the atmosphere-only climate model HadGEM3-GA7.1. The model contains biases in the aerosol seasonal variability over the Southern Ocean (40°S to 60°S), which cascade to uncertainties in aerosol-cloud interactions. Aerosols over the Southern Ocean are primarily natural in origin, such as sea spray aerosol and sulfate aerosol formed by phytoplankton-produced dimethyl sulfide (DMS).

The current sulfate chemistry scheme implemented in the model simplifies the oxidation pathways for DMS, which has been identified as a major source of the seasonal bias present. The simulations performed here incorporate a comprehensive sulfate scheme in both the gas and aqueous-phase. An intermediate complexity biogeochemical dynamic model, MEDUSA, simulated a global climatology of seawater DMS, which is compared with a seawater DMS observational dataset from 2011. We compared the seasonality of sulfate aerosols over the Southern Ocean, and the global distribution using the two seawater DMS climatologies. Simulated aerosols over the Southern Ocean were evaluated against satellite and in-situ observations. The results show the impact of seawater DMS on sulfate aerosols and their influence on cloud formation.

How to cite: Bhatti, Y., Revell, L., McDonald, A., and Willaims, J.: Global Climate Model Simulations of Natural Aerosols over the Southern Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-195,, 2020.

Faustine Mascaut, Olivier Pujol, Jérôme Brioude, Bert Verreyken, Raphaël Peroni, Luc Blarel, Thierry Podvin, Jean-Marc metzger, Karine Sellegri, and Philippe Goloub

We present the results of the AEROMARINE field campaign which took place in the boreal spring 2019 off the coast of Reunion island in the South West Indian Ocean basin. The southern Indian Ocean is of major interest for the study of marine aerosols, their distribution and variability [1]. Nine instrumented light plane flights and a ground-based microwave radiometer were used during the AEROMARINE field campaign. These measurements were compared with the long-term measurements of the AERONET sun-photometer (based in Saint Denis, Reunion Island) and various instruments of the high altitude Maido Observatory (2200m above sea level, Reunion island). These results were analyzed using different model outputs: (i) the AROME mesoscale weather forecast model to work on the thermodynamics of the boundary layer, (ii) the FLEXPART-AROME Lagrangian particle dispersion model to assess the geographical and vertical origin of air masses, and (iii) the chemical transport model CAMS (Copernicus Atmosphere Monitoring Service) to work on the aerosol chemical composition of air masses. These measurements allowed us to determine the background concentration of natural marine aerosols and to highlight that (1) the atmospheric layers above 1500m are in the free troposphere and are mainly composed of aerosols from the regional background and (2) that the local environment (ocean or island) has little impact on the measured concentrations. Marine aerosols emitted locally are mostly measured in the lower atmospheric layers (below 500m). The daytime marine aerosol distributions in the free troposphere measured by the aircraft were compared to the aerosol distribution measured at the high altitude Maido observatory at night when the observatory is located in the free troposphere.  We also found that the CAMS reanalyses overestimated the aerosol optical depth in this region. Finally, our study confirms, with no ambiguity, that the AERONET station in Saint Denis (Reunion island) can be considered as a representative marine station in the tropics [2]

[1]  I.  Koren,  G.  Dagan,  and  O.  Altaratz.   From  aerosol-limited  to  invigoration  of  warm  convective clouds. Science, 344 (6188) : 1143–1146, 2014.
[2]  P. Hamill, M. Giordano, C. Ward, D. Giles, and B. Holben.  An aeronet-based aerosol classification using the mahalanobis distance. Atmospheric Environment, 140 : 213–233,2016.

How to cite: Mascaut, F., Pujol, O., Brioude, J., Verreyken, B., Peroni, R., Blarel, L., Podvin, T., metzger, J.-M., Sellegri, K., and Goloub, P.: Aerosol characterization in an oceanic context around Reunion island (AEROMARINE field campaign), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2729,, 2021.

Bernd Heinold, Holger Baars, Matthew Christensen, Anne Kubin, Kevin Ohneiser, Kerstin Schepanski, Roland Schrödner, Fabian Senf, and Ina Tegen

Record wildfires affected Australia from December 2019 to early 2020. Massive plumes of fire pollutants were lifted into the upper troposphere and even into the stratosphere by pyro-convection triggered by the intense heat of the fires. Subsequently the smoke aerosol was transported over thousands of kilometres eastwards at above 20 km altitude as Lidar observations in South America and satellite imagery show. Space and ground-based remote sensing of aerosol optical thickness indicate a temporary substantial increase in aerosol loading over large parts of the Southern Hemisphere, which offset the usual hemispheric contrast in aerosol. In addition to the massive impact on air quality at Australia’s east coast, this had important effects on the hemisphere-wide radiation budget.

We investigate the dispersal of the fire smoke aerosol and its radiative effects with the global aerosol-climate model ECHAM6.3-HAM2.3. Biomass burning emissions are prescribed by daily satellite-based estimates from the Global Fire Assimilation System (GFAS). As the horizontal model resolution is too coarse to explicitly resolve convection, the injection height of Australian fire smoke is set to heights between 5 and 15 km and varied in terms of sensitivity studies. The model results for late 2019 and early 2020 are evaluated with ground and satellite remote sensing measurements, as well as contrasted with smoke results for years with low Australian wildfire emissions. The sensitivity results show how the fire injection heights affect the evolution of the smoke plume but also what role radiatively induced self-lifting plays. According to the model, the 2019/20 Australian wildfires considerably perturbed the radiation budget of the Southern Hemisphere. Due to large transport heights relative to clouds and a long lifetime of smoke particles in the stratosphere, the solar irradiance at ground averaged from January to March 2020 decreased by more than 1 W m-2 for the Southern Hemisphere, which corresponds roughly to the short-term cooling caused by a large volcanic eruption, while the elevated smoke layers experienced significant absorptive heating.

Considering the recent series of extreme wildfires globally and their probably further increasing occurance in a changing climate,  these results indicate a need for larger attention to pyro-convection in global climate modelling.

How to cite: Heinold, B., Baars, H., Christensen, M., Kubin, A., Ohneiser, K., Schepanski, K., Schrödner, R., Senf, F., and Tegen, I.: Direct radiative effects of smoke aerosol during the extreme 2019/2020 Australian wildfire season, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7286,, 2021.

Tero Mielonen, Taina Yli-Juuti, Liine Heikkinen, Antti Arola, Mikael Ehn, Sini Isokääntä, Helmi-Marja Keskinen, Markku Kulmala, Anton Laakso, Antti Lipponen, Krista Luoma, Santtu Mikkonen, Tuomo Nieminen, Pauli Paasonen, Tuukka Petäjä, Sami Romakkaniemi, Juha Tonttila, Harri Kokkola, and Annele Virtanen

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 have potentially important implications on regional aerosol radiative forcing. Here, we have used long-term aerosol composition and temperature data measurements from a boreal forest site together with remote sensing observations of aerosol and cloud properties to investigate the effect of increasing temperature on organic aerosol mass loadings, and further on aerosol direct and indirect radiative effects. The analysis was based on 7 years of measurements done at Hyytiälä, Southern Finland, and they cover the summer months (July-August) between 2012-2018. We limited the analyses to these summer months to isolate the temperature dependence of the organic mass loadings from the seasonal effects arising from the vegetation growth cycle. Our analysis showed that organic aerosol loadings and cloud condensation nuclei concentrations increased in concert with surface temperature. Furthermore, we found that cloud reflectivity increased when the organic aerosol loadings increased. This research presents the first direct observational evidence on the effect of BSOA on cloud properties and their climatic significance.

How to cite: Mielonen, T., Yli-Juuti, T., Heikkinen, L., Arola, A., Ehn, M., Isokääntä, S., Keskinen, H.-M., Kulmala, M., Laakso, A., Lipponen, A., Luoma, K., Mikkonen, S., Nieminen, T., Paasonen, P., Petäjä, T., Romakkaniemi, S., Tonttila, J., Kokkola, H., and Virtanen, A.: The Climatic Significance of Organic Aerosol in the Boreal Region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8319,, 2021.