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Dusty cirrus clouds are extended optically thick cirrocumulus decks that occur during strong mineral dust events. So far they have mostly been documented over Europe associated with dust-infused baroclinic storms. Since today's global numerical weather prediction models neither predict mineral dust distributions nor consider the interaction of dust with cloud microphysics, they cannot simulate this phenomenon. We postulate that the dusty cirrus forms through a mixing instability of moist clean air with drier dusty air. A corresponding sub-grid parameterization is suggested and tested in the ICOsahedral Nonhydrostatic model with Aerosol and Reactive Trace gases (ICON-ART). Only with the help of this parameterization is ICON-ART able to simulate the formation of the dusty cirrus, which leads to substantial improvements in cloud cover and radiative fluxes compared to simulations without this parameterization. A statistical evaluation over six Saharan dust events with and without observed dusty cirrus shows robust improvements in cloud and radiation scores. The ability to simulate dusty cirrus formation removes the linear dependency on mineral dust aerosol optical depth from the bias of the radiative fluxes. For the six Saharan dust episodes investigated in this study, the formation of dusty cirrus clouds is the dominant aerosol–cloud–radiation effect of mineral dust over Europe. [ABSTRACT FROM AUTHOR]

Urban aerosol pollution was analyzed over the Moscow megacity region using the COSMO-ART (COSMO – COnsortium for Small-scale MOdelling, ART – Aerosols and Reactive Trace gases) online coupled mesoscale model system and intensive measurement campaigns at the Moscow State University Meteorological Observatory (MSU MO, 55.707 ∘ N, 37.522 ∘ E) during the April–May period in 2018 and 2019. We analyzed mass concentrations of particulate matter with diameters smaller than 10 µm (PM 10), black carbon (BC) and aerosol gas precursors (NO x , SO 2 , CH x) as well as columnar aerosol parameters for fine and coarse modes together with different meteorological parameters, including an index characterizing the intensity of particle dispersion (IPD). Both model and experimental datasets have shown a statistically significant linear correlation of BC with NO 2 and PM 10 mass concentrations, which indicates mostly common sources of emissions of these substances. There was a pronounced increase in the BC/PM10 ratio from 0.7 % to 5.9 %, with the decrease in the IPD index related to the amplification of the atmospheric stratification. We also found an inverse dependence between the BC/PM10 ratio and columnar single-scattering albedo (SSA) for the intense air mixing conditions. This dependence together with the obtained negative correlation between wind speed and BC/PM10 may serve as an indicator of changes in the absorbing properties of the atmosphere due to meteorological factors. On average, the relatively low BC / PM 10 ratio (for urban regions) of 4.7 % is the cause of the observed relatively high SSA = 0.94 in Moscow. Using long-term parallel aerosol optical depth (AOD) measurements over the 2006–2020 period at the MSU MO and under upwind clean background conditions at Zvenigorod Scientific Station (ZSS) of the IAP RAS (55.7 ∘ N, 36.8 ∘ E), we estimated the urban component of AOD (AOD urb) and some other parameters as the differences at these sites. The annual mean AOD urb at 550 nm was about 0.021 with more than 85 % of the fine aerosol mode. The comparisons between AOD urb obtained from the model and measurements during this experiment have revealed a similar level of aerosol pollution of about AOD urb=0.015 –0.019, which comprised 15 %–19 % of the total AOD at 550 nm. The urban component of PM 10 (PM 10urb) was about 16 µgm-3 according to the measurements and 6 µgm-3 according to the COSMO-ART simulations. We obtained a pronounced diurnal cycle of PM 10urb and urban BC (BC urb) as well as their strong correlation with the IPDs. With the IPD index change from 3 to 1 at night, there was about a 4 times increase in PM 10urb (up to 30–40 µgm-3) and a 3 times increase in BC urb (up to 3–3.5 µgm-3). At the same time, no pronounced daily cycle was found for the columnar urban aerosol component (AOD urb), although there was a slight increase in model AOD urb at night. [ABSTRACT FROM AUTHOR]

In June 2019, the Raikoke volcano, Kuril Islands, emitted 0.4– 1.8×109 kg of very fine ash and 1– 2×109 kg of SO2 up to 14 km into the atmosphere. The eruption was characterized by several eruption phases of different duration and height summing up to a total eruption length of about 5.5 h. Resolving such complex eruption dynamics is required for precise volcanic plume dispersion forecasts. To address this issue, we coupled the atmospheric model system ICON-ART (ICOsahedral Nonhydrostatic with the Aerosols and Reactive Trace gases module) with the 1D plume model FPlume to calculate the eruption source parameters (ESPs) online. The main inputs are the plume heights for the different eruption phases that are geometrically derived from satellite data. An empirical relationship is used to derive the amount of very fine ash (particles <32 µm), which is relevant for long-range transport in the atmosphere. On the first day after the onset of the eruption, the modeled ash loading agrees very well with the ash loading estimated from AHI (Advanced Himawari Imager) observations due to the resolution of the eruption phases and the online treatment of the ESPs. In later hours, aerosol dynamical processes (nucleation, condensation, and coagulation) explain the loss of ash in the atmosphere in agreement with the observations. However, a direct comparison is partly hampered by water and ice clouds overlapping the ash cloud in the observations. We compared 6-hourly means of model and AHI data with respect to the structure, amplitude, and location (SAL method) to further validate the simulated dispersion of SO2 and ash. In the beginning, the structure and amplitude values for SO2 differed largely because the dense ash cloud leads to an underestimation of the SO2 amount in the satellite data. On the second and third day, the SAL values are close to zero for all parameters (except for the structure value of ash), indicating a very good agreement of the model and observations. Furthermore, we found a separation of the ash and SO2 plume after 1 d due to particle sedimentation, chemistry, and aerosol–radiation interaction. The results confirm that coupling the atmospheric model system and plume model enables detailed treatment of the plume dynamics (phases and ESPs) and leads to significant improvement of the ash and SO2 dispersion forecast. This approach can benefit the operational forecast of ash and SO2 especially in the case of complex and noncontinuous volcanic eruptions like that of Raikoke in 2019. [ABSTRACT FROM AUTHOR]

A correct and reliable forecast of volcanic plume dispersion is vital for aviation safety. This can only be achieved by representing all responsible physical and chemical processes (sources, sinks, and interactions) in the forecast models. The representation of the sources has been enhanced over the last decade, while the sinks and interactions have received less attention. In particular, aerosol dynamic processes and aerosol–radiation interaction are neglected so far. Here we address this gap by further developing the ICON-ART (ICOsahedral Nonhydrostatic – Aerosols and Reactive Trace gases) global modeling system to account for these processes. We use this extended model for the simulation of volcanic aerosol dispersion after the Raikoke eruption in June 2019. Additionally, we validate the simulation results with measurements from AHI (Advanced Himawari Imager), CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization), and OMPS-LP (Ozone Mapping and Profiling Suite-Limb Profiler). Our results show that around 50 % of very fine volcanic ash mass (particles with diameter d<30 µ m) is removed due to particle growth and aging. Furthermore, the maximum volcanic cloud top height rises more than 6 km over the course of 4 d after the eruption due to aerosol–radiation interaction. This is the first direct evidence that shows how cumulative effects of aerosol dynamics and aerosol–radiation interaction lead to a more precise forecast of very fine ash lifetime in volcanic clouds. [ABSTRACT FROM AUTHOR]

This study underlines the important role of the transported black carbon (BC) mass concentration in the West African monsoon (WAM) area. BC was measured with a micro-aethalometer integrated in the payload bay of the unmanned research aircraft ALADINA (Application of Light-weight Aircraft for Detecting IN situ Aerosol). As part of the DACCIWA (Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa) project, 53 measurement flights were carried out at Savè, Benin, on 2–16 July 2016. A high variability of BC (1.79 to 2.42±0.31 µ g m -3) was calculated along 155 vertical profiles that were performed below cloud base in the atmospheric boundary layer (ABL). In contrast to initial expectations of primary emissions, the vertical distribution of BC was mainly influenced by the stratification of the ABL during the WAM season. The article focuses on an event (14 and 15 July 2016) which showed distinct layers of BC in the lowermost 900 m above ground level (a.g.l.). Low concentrations of NOx and CO were sampled at the Savè supersite near the aircraft measurements and suggested a marginal impact of local sources during the case study. The lack of primary BC emissions was verified by a comparison of the measured BC with the model COSMO-ART (Consortium for Small-scale Modelling–Aerosols and Reactive Trace gases) that was applied for the field campaign period. The modelled vertical profiles of BC led to the assumption that the measured BC was already altered, as the size was mainly dominated by the accumulation mode. Further, calculated vertical transects of wind speed and BC presume that the observed BC layer was transported from the south with maritime inflow but was mixed vertically after the onset of a nocturnal low-level jet at the measurement site. This report contributes to the scope of DACCIWA by linking airborne BC data with ground observations and a model, and it illustrates the importance of a more profound understanding of the interaction between BC and the ABL in the WAM region. [ABSTRACT FROM AUTHOR]

Vast stretches of agricultural land in southern and central Africa are burnt between June and September each year, which releases large quantities of aerosol into the atmosphere. The resulting smoke plumes are carried west over the Atlantic Ocean at altitudes between 2 and 4 km. As only limited observational data in West Africa have existed until now, whether this pollution has an impact at lower altitudes has remained unclear. The Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) aircraft campaign took place in southern West Africa during June and July 2016, with the aim of observing gas and aerosol properties in the region in order to assess anthropogenic and other influences on the atmosphere. Results presented here show that a significant mass of aged accumulation mode aerosol was present in the southern West African monsoon layer, over both the ocean and the continent. A median dry aerosol concentration of 6.2 µ g m -3 (standard temperature and pressure, STP) was observed over the Atlantic Ocean upwind of the major cities, with an interquartile range from 5.3 to 8.0 µ g m -3. This concentration increased to a median of 11.1 µ g m -3 (8.6 to 15.7 µ g m -3) in the immediate outflow from cities. In the continental air mass away from the cities, the median aerosol loading was 7.5 µ g m -3 (5.9 to 10.5 µ g m -3). The accumulation mode aerosol population over land displayed similar chemical properties to the upstream population, which implies that upstream aerosol is a significant source of aerosol pollution over the continent. The upstream aerosol is found to have most likely originated from central and southern African biomass burning. This demonstrates that biomass burning plumes are being advected northwards, after being entrained into the monsoon layer over the eastern tropical Atlantic Ocean. It is shown observationally for the first time that they contribute up to 80 % to the regional aerosol loading in the monsoon layer over southern West Africa. Results from the COSMO-ART (Consortium for Small-scale Modeling – Aerosol and Reactive Trace gases) and GEOS-Chem models support this conclusion, showing that observed aerosol concentrations over the northern Atlantic Ocean can only be reproduced when the contribution of transported biomass burning aerosol is taken into account. As a result, the large and growing emissions from the coastal cities are overlaid on an already substantial aerosol background. Simulations using COSMO-ART show that cloud droplet number concentrations can increase by up to 27 % as a result of transported biomass burning aerosol. On a regional scale this renders cloud properties and precipitation less sensitive to future increases in anthropogenic emissions. In addition, such high background loadings will lead to greater pollution exposure for the large and growing population in southern West Africa. These results emphasise the importance of including aerosol from across country borders in the development of air pollution policies and interventions in regions such as West Africa. [ABSTRACT FROM AUTHOR]

We conducted a 6-week measurement campaign in summer 2016 at a rural site about 11 km north of the city of Karlsruhe in southwest Germany in order to study the chemical composition and origin of aerosols in the upper Rhine valley. In particular, we deployed a single-particle mass spectrometer (LAAPTOF) and an aerosol mass spectrometer (AMS) to provide complementary chemical information on aerosol particles smaller than 2.5 µ m. For the entire measurement period, the total aerosol particle mass was dominated by sodium salts, contributing on average (36±27) % to the total single particles measured by the LAAPTOF. The total particulate organic compounds, sulfate, nitrate, and ammonium contributed on average (58±12) %, (22±7) %, (10±1) %, and (9±3) % to the total non-refractory particle mass measured by the AMS. Positive matrix factorization (PMF) analysis for the AMS data suggests that the total organic aerosol (OA) consisted of five components, including (9±7) % hydrocarbon-like OA (HOA), (16±11) % semi-volatile oxygenated OA (SV-OOA), and (75±15) % low-volatility oxygenated OA (LV-OOA). The regional transport model COSMO-ART was applied for source apportionment and to achieve a better understanding of the impact of complex transport patterns on the field observations. Combining field observations and model simulations, we attributed high particle numbers and SO2 concentrations observed at this rural site to industrial emissions from power plants and a refinery in Karlsruhe. In addition, two characteristic episodes with aerosol particle mass dominated by sodium salts particles comprising (70±24) % of the total single particles and organic compounds accounting for (77±6) % of total non-refractory species, respectively, were investigated in detail. For the first episode, we identified relatively fresh and aged sea salt particles originating from the Atlantic Ocean more than 800 km away. These particles showed markers like m/z 129 C5H7NO3+ , indicating the influence of anthropogenic emissions modifying their composition, e.g. from chloride to nitrate salts during the long-range transport. For a 3 d episode including high organic mass concentrations, model simulations show that on average (74±7) % of the particulate organics at this site were of biogenic origin. Detailed model analysis allowed us to find out that three subsequent peaks of high organic mass concentrations originated from different sources, including local emissions from the city and industrial area of Karlsruhe, regional transport from the city of Stuttgart (∼64 km away), and potential local night-time formation and growth. Biogenic (forest) and anthropogenic (urban) emissions were mixed during transport and contributed to the formation of organic particles. In addition, topography, temperature inversion, and stagnant meteorological conditions also played a role in the build-up of higher organic particle mass concentrations. Furthermore, the model was evaluated using field observations and corresponding sensitivity tests. The model results show good agreement with trends and concentrations observed for several trace gases (e.g. O3 , NO2 , and SO2) and aerosol particle compounds (e.g. ammonium and nitrate). However, the model underestimates the number of particles by an order of magnitude and underestimates the mass of organic particles by a factor of 2.3. The discrepancy was expected for particle number since the model does not include all nucleation processes. The missing organic mass indicates either an underestimated regional background or missing sources and/or mechanisms in the model, like night-time chemistry. This study demonstrates the potential of combining comprehensive field observations with dedicated transport modelling to understand the chemical composition and complex origin of aerosols. [ABSTRACT FROM AUTHOR]

We present a new emissions module for the ICON (ICOsahedral Non-hydrostatic)-ART (Aerosols and ReactiveTrace gases) modelling framework. The emissions module processes external flux data sets and increments the tracer volume mixing ratios in the boundary layer accordingly. In addition, the module for online calculations of biogenic emissions (MEGAN2.1) is implemented in ICON-ART and can replace the offline biogenic emission data sets. The performance of the emissions module is illustrated with simulations of acetone, using a simplified chemical depletion mechanism based on a reaction with OH and photolysis only. In our model setup, we calculate a tropospheric acetone lifetime of 33 days, which is in good agreement with the literature. We compare our results with airborne IAGOS-CARIBIC measurements in the upper troposphere and lowermost stratosphere (UTLS) in terms of phase and amplitude of the annual cycle. In all our ICON-ART simulations the general seasonal variability is well represented but questions remain concerning the magnitude of the acetone emissions and its atmospheric lifetime. We conclude that the new emissions module performs well and allows the simulation of the annual cycles of emissions dominatedconcentrations even with a simple chemistry only. [ABSTRACT FROM AUTHOR]

Aerosols of volcanic origin, such as ash and sulfate particles, can impose a severe hazard onaircrafts as well as they can influence weather and climate. Hence, having an exactrepresentation of these particles in numerical weather and climate models is ofgreat interest not only for weather forecasters and climate modelers, but also for airtraffic safety. For this purpose, in addition to a transport scheme for the aerosolparticles and reactive trace gases, the emission of volcanic ash and gases has to beparametrized correctly as well as aerosol dynamic processes have to be considered, suchas the formation of secondary particles, particle-particle interaction, and removalprocesses. The global modeling system ICON-ART has been used before to simulate thedistribution of volcanic ash and its radiative feedback after volcanic eruptions. In thisconnection, the emission of volcanic ash has been parametrized. However, duringthese studies the chemical properties of volcanic ash particles could not have beenaltered. With the current work, the global modeling system ICON-ART is extended towards acomprehensive representation of aerosol dynamic processes, which allows the simulation ofaging processes for volcanic ash aerosol. The improved aerosol module AERODYN(AEROsol DYNamic) includes a scheme for particle-particle interaction through coagulationand particle growth due to condensation of gaseous matter onto the particle. Furthermore,Weimer et al. (2017) implemented a simplified OH chemistry scheme into ICON-ARTthat enables the conversion of volcanic SO2 into sulfuric acid, which, in a secondstep, can nucleate into sulfate particles or condensate onto already existing aerosolparticles. First studies with the improved aerosol module AERODYN in ICON-ART have beenconducted for the Eyjafjallajökull eruption in May 2010 and the Pinatubo eruption of 1991. Itis shown that the transformation of SO2 into secondary volcanic aerosol (sulfate particles) aswell as the aging of ash particles due to condensation of sulfate, nitrate, ammonium and wateronto them alters the chemical composition of the ash plume, modifies the SO2 budget, andchanges the sedimentation velocity and, therefore, the removal of internally mixed aerosolparticles. [ABSTRACT FROM AUTHOR]

Aeolian dust, the most dominant atmospheric aerosol by mass, influences the weather and climate directly through absorbing and scattering the radiation. Particle size distribution (PSD) controls the magnitude of these impacts through modulating the dust residence time in the atmosphere and optical properties. Although the dust PSD varies during the atmospheric transport, current models usually neglect the effect of these variations on dust optical properties. This study investigates the impact of variable PSD on dust optical properties and radiative impacts using the next-generation atmospheric modeling system ICON-ART (ICOsahedral Nonhydrostatic with Aerosols and Reactive Trace gases). Two sets of numerical experiments are conducted assuming fixed and variable PSD. A parameterization is developed to account for the effect of variable PSD on dust optical properties in the model. This parameterization is then implemented in ICON-ART to simulate a period of 1 month on a global grid with 80 km horizontal resolution. Results show that the consideration of a variable PSD increases the dust AOD. However, the magnitude of the changes depends on the dominant size modes. Although the optical properties of the fine mode show the highest sensitivity to the variable PSD, the median diameter of this mode hardly changes during transport. Thus, the new parametrization does not have a significant impact on AOD where fine mode is dominant. In contrast, when coarse mode is prevailing, the increase of AOD is more pronounced. This makes the surface slightly warmer (+0.2 K) in the source regions. [ABSTRACT FROM AUTHOR]