AS3.17

Aerosol induced absorption of shortwave radiation can modify the climate through local atmospheric heating, which affects lapse rates, precipitation, and cloud formation. Presently, the total amount of aerosol absorption is poorly constrained, and the main absorbing aerosol species (black carbon (BC), organic aerosols (OA) and mineral dust) are diversely quantified in global climate models. As part of the third phase of the AeroCom model intercomparison initiative (AeroCom Phase III) we here document the distribution and magnitude of aerosol absorption in current global aerosols models and quantify the sources of intermodel spread, highlighting the difficulties of attributing absorption to different species. 15 models have provided total present-day absorption at 550 nm (using year 2010 emissions), 11 of which have provided absorption per absorbing species. Of the summed component AAOD, 60 % (range 36-84%) is estimated to be due to BC, 31 % (12-49%) is due to dust and 11% (0-24%) is due to OA, however the components are not independent in terms of their absorbing efficiency, and in models with internal mixtures of absorbing aerosols, a major challenge is the lack of a common and simple method to attribute absorption to the different absorbing species. We discuss challenges of attributing absorption to different species, we compare burden, refractive indices, and density, and we contrast models with internal mixing to models with external mixing. The difference in spectral dependency between the models is striking.

How to cite: Sand, M., Samset, B., and Myhre, G. and the AeroCom modellers: Aerosol absorption in global models from AeroCom Phase III, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9272, https://doi.org/10.5194/egusphere-egu22-9272, 2022.

Aerosol absorption is a key property to assess the radiative impacts of aerosols on climate at both global and regional scales. The aerosol physico-chemical and optical properties remain not sufficiently constrained in climate models, with difficulties to properly represent both the aerosol load and their absorption properties in clear and cloudy scenes, especially for absorbing biomass burning aerosols (BBA). In this study we focus on biomass burning (BB) particle plumes transported above clouds over the southeast Atlantic (SEA) region off the southwest coast of Africa, in order to improve the representation of their physico-chemical and absorption properties. The methodology is based on aerosol regional numerical simulations from the WRF-Chem coupled meteorology–chemistry model combined with a detailed inventory of BB emissions and various sets of innovative aerosol remote sensing observations, both in clear and cloudy skies from the POLDER-3/PARASOL space sensor. Current literature indicates that some organic aerosol compounds (OC), called brown carbon (BrOC), primarily emitted by biomass combustion absorb the ultraviolet-blue radiation more efficiently than pure black carbon (BC). We exploit this specificity by comparing the spectral dependence of the aerosol single scattering albedo (SSA) derived from the POLDER-3 satellite observations in the 443-1020 nm wavelength range with the SSA simulated for different proportions of BC, OC and BrOC at the source level, considering the homogeneous internal mixing state of particles. These numerical simulation experiments are based on two main constraints: maintaining a realistic aerosol optical depth both in clear and above cloudy scenes and a realistic BC-to-OC mass ratio. Modelling experiments are presented and discussed to link the chemical composition with the absorption properties of BBA and to provide estimates of the relative proportions of black, organic and brown carbon in the African BBA plumes transported over the SEA region for July 2008. The absorbing fraction of organic aerosols in the BBA plumes, i.e., BrOC, is estimated at 2 % to 3 %. The simulated mean SSA are 0.81 (565 nm) and 0.84 (550 nm) in clear and above cloudy scenes, respectively, in good agreement with those retrieved by POLDER-3 (0.85±0.05) at 565 nm in clear sky and at 550 nm above clouds) for the studied period.

How to cite: Siméon, A., Waquet, F., Péré, J.-C., Ducos, F., Thieuleux, F., Peers, F., Turquety, S., and Chiapello, I.: Combining POLDER-3 satellite observations and WRF-Chem numerical simulations to derive biomass burning aerosol properties over the southeast Atlantic region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4729, https://doi.org/10.5194/egusphere-egu22-4729, 2022.

Biomass-burning aerosol layers overlaying stratocumulus clouds are frequent over the Southeast Atlantic during the southern African fire season (June-October). This scenario can trigger a rich set of aerosol-cloud-radiation interactions with climatic consequences that are still poorly quantified. Although satellites and in-situ measurements provide useful information on these situations, the covariance between aerosols and meteorology makes it difficult to disentangle any causal aerosol impacts on stratocumulus clouds, a problem that can be avoided when using models. In this work, we have incorporated aerosol-radiation interactions into the large-eddy simulation code MIMICAV5 to study how a biomass burning aerosol layer (composed of black carbon and organic carbon) affects an underlying stratocumulus cloud over the Southeast Atlantic. More specifically, we explore how the arrival time (time of the day during the simulation) of the absorbing aerosol layer cloud affects the underlying stratocumulus cloud properties. In addition, we explore the susceptibility of cloud droplet number concentration in the stratocumulus cloud to the absorbing aerosol number concentration above the cloud.

How to cite: Baró Pérez, A., Ekman, A., Schwarz, M., Savre, J., Bender, F., Devasthale, A., Tonttila, J., and Kokkola, H.: Exploring impacts of absorbing aerosol layers on underlying stratocumulus clouds using large-eddy simulation with explicit aerosol-radiation interactions., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4532, https://doi.org/10.5194/egusphere-egu22-4532, 2022.

The West African Monsoon (WAM) is a complex system depending on global climate influences and multiple regional environmental factors. Central and Southern African biomass-burning (SABB) aerosols have been shown to perturb WAM during episodic northward inter-hemispheric transport events, but a possible dynamical connection between the core of the SABB aerosol outflow and the WAM system remains unexplored. Through regional climate modeling experiments, we show that SABB aerosols can indeed impact WAM dynamics via two competitive regional scale and inter-hemispheric dynamical feedbacks originating from (i) enhanced diabatic heating occurring in the Southeastern Atlantic low-cloud deck region, and (ii) aerosol and cloud-induced sea surface temperature cooling. These mechanisms, related to aerosol direct, semi-direct, and indirect effects, are shown to have different seasonal timings, resulting in a reduction of June to September WAM precipitation, while possibly enhancing late-season rainfall in WAM coastal areas.

How to cite: solmon, F., elguindi, N., mallet, M., flamant, C., and formenti, P.: West African monsoon precipitation impacted by the South Eastern Atlantic biomass burning aerosol outflow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2240, https://doi.org/10.5194/egusphere-egu22-2240, 2022.

Light absorbing organic aerosol such as brown carbon can impact the climate through warming. Atmospheric processing including evaporation and photochemical ageing can modify the microphysical and optical properties of aerosol which in turn affects how aerosols affect the climate. Currently the change in microphysical and optical properties induced by atmospheric processing is not well understood.

Previously we have measured the UV-visible absorbance spectra of single acoustically levitated droplets of brown carbon as they evaporate. We measured a shift in the absorbance maximum towards the visible region of the spectrum for evaporating droplets of humic acid and water-soluble extracts of wood smoke aerosol. The shift in the absorbance maximum has important implications for the climate as it results in an increased overlap of the aerosol absorbance with actinic radiation. Building on this work and acknowledging the complex composition of real atmospheric aerosols, here we report absorbance measurements of evaporating droplets containing brown carbon and ammonium sulfate. Initial results show differences in absorbance spectra compared to spectra without ammonium sulfate that could indicate the formation of new chemical species as the droplets evaporate and are illuminated.

How to cite: Jones, S. and Donaldson, D. J.: Effect of ammonium sulfate on the absorbance spectra of acoustically levitated brown carbon containing droplets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11041, https://doi.org/10.5194/egusphere-egu22-11041, 2022.

Emissions of carbonaceous aerosols (black carbon (BC) and organic aerosol (OA)) from biomass burning have important climate and human health impacts. Not only the primary emissions are complicated by combustion phases, but also the evolution after emission is not well understood. In this study, single plumes from residential wood burning, extracted from either flaming or smoldering phase, were injected into our novel chamber, to investigate their evolution in real atmospheric conditions with or without solar radiation. Initial compositions of flaming or smoldering plumes were dominated by BC or OA respectively. Replicable results showed that in light, smoldering plumes had faster secondary OA (SOA) formation than flaming. Furanic and carboxylic acid compounds were found to be the main gaseous precursors and products, respectively. Evaporation and photooxidation concurrently caused increased oxidation in the beginning, but at a later stage of evolution, SOA evolution showed remarkabledivergence: enhanced oxidation for smoldering but decreased for flaming plumes, leading to a higher oxygen-to-carbon ratio for smoldering than flaming up to 0.25. OA from flaming conditions showed a higher absorptivity than from smoldering conditions, as OA is mostly internally and externally mixed with BC, respectively. For flaming (smoldering), the imaginary refractive index of OA (k_OA) was initially at 0.03 ± 0.01 (0.001) and 0.15 ± 0.02 (0.05 ± 0.02) at λ = 781 and 405 nm, respectively, with a half-decay time of 2−3 h in light but a <40% decrease under dark within 5 h. The production of less-absorbing SOA in the first 1−2 h and possible subsequent photobleaching of chromophores contributed to the decrease of k_OA. The enhanced abundance but decreased absorptivity of coatings on BC resulted in a relatively maintainable absorptivity of BC-containing particles during evolution. Distinct particulate/gas emissions and resultant evolutions at different combustion phases should be therefore considered in evaluating the impacts of biomass burning emissions.

Dantong Liu*, Siyuan Li, Dawei Hu, Shaofei Kong*, Yi Cheng, Yangzhou Wu, Shuo Ding, Kang Hu, Shurui Zheng, Qin Yan, Huang Zheng, Delong Zhao, Ping Tian, Jianhuai Ye, Mengyu Huang, Deping Ding: Evolution of Aerosol Optical Properties from Wood Smoke in Real Atmosphere Influenced by Burning Phase and Solar Radiation, Environmental Science & Technology, 55(9), 5677–5688, 10.1021/acs.est.0c07569, 2021.

Siyuan Li, Dantong Liu*, Dawei Hu, Shaofei Kong, Yangzhou Wu, Shuo Ding, Yi Cheng, Hao Qiu, Shurui Zheng, Qin Yan, Huang Zheng, Kang Hu, Jiale Zhang, Delong Zhao, Quan Liu, Jiujiang Sheng, Jianhuai Ye, Hui He, Deping Ding: Evolution of organic aerosol from wood smoke influenced by burning phase and solar radiation, Journal of Geophysical Research – Atmospheres, 126(8), 10.1029/2021JD034534, 2021.

How to cite: Liu, D. and Li, S.: Evolution of Aerosols From Wood Smoke Influenced by Burning Phase and Solar Radiation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2094, https://doi.org/10.5194/egusphere-egu22-2094, 2022.

Global mean lower stratosphere temperatures rose abruptly in January 2020 reaching values not experienced since the early 1990s. Anomalous lower stratospheric temperatures were recorded for 4 months at highly statistically significant levels (p-values of 0.0004 to 0.02). While the warming event of 1991-1993 has been definitively attributed to absorption of sunlight by stratospheric sulfate from the eruption of Pinatubo, no candidate volcanic eruption for explaining the 2020 stratospheric heating exists. Here, we use a combination of satellite and surface-based remote sensing observations to derive a time-series of stratospheric biomass burning aerosol optical depths originating from the intense 2019/20 S.E. Australian wildfires and apply these to a state-of-the-art climate model. We show beyond doubt that the biomass burning aerosols emitted by the S.E. Australian wildfires are the cause of this lower stratospheric warming, with implications for stratospheric dynamics and stratospheric ozone should this type of event become more frequent in the future.

How to cite: Damany-Pearce, L., Johnson, B., Wells, A., Osborne, M., Allan, J., Belcher, C., and Haywood, J.: Australian Wildfires cause the largest stratospheric warming since Pinatubo., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7918, https://doi.org/10.5194/egusphere-egu22-7918, 2022.

In the follow-up of the Australian”Black Summer” event that persisted from August 2019 to March 2020, we present the optical properties of the stratospheric aerosols injected into the atmosphere by these wildfires. The outbreak of pyrocumulonimbus(PyroCb) activity triggered between 2019/12/29 and 2020/01/04 have raised the stratospheric aerosol load of the Southern Hemisphere to unprecedented levels.  Long-range transport brought some of the plumes down to the Antarctic region, where general circulation patterns kept them circling around the continent.  The 532nm Rayleigh/Mie/Raman ground-based lidar of the French Antarctic station Dumont d’Urville (DDU,66.6°S – 140°E) acquired unprecedented time series of these carbonaceousaerosols starting approximately days after the injection and up to the most recent measurements in October 2019 where local radiosonde reported anomalous ozone depletion as compared to the decadal average.  The lidar provides a first and unique time series at high vertical and temporal resolution, complemented by satellite measurements from OMI, OMPS and MLS. Aerosol backscatter ratio decreases from 1.9 to 1.2 between January and June 2020.  Aerosol origin and persistence are characterized, as well as their optical properties and vertical distribution on several months.

In this presentation we will introduce the station and instrumental capabilities along with the latest measurements following the publication of Tencé et al., jgr, 2022.

How to cite: Tencé, F. and Jumelet, J.: Australian Black Summer smoke observed by lidar at the French Antarctic station Dumont d’Urville, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11290, https://doi.org/10.5194/egusphere-egu22-11290, 2022.

Multiple wildfire episodes have been observed in Greece during August 2021, after a historic heatwave, with temperatures exceeding 45°C. Two of the most destructive wildfires were in Attica and Euboea with smoke plumes covering the city of Athens and affecting significantly not only the air-quality and also the levels of surface solar radiation. During these events, spectral optical properties of aerosols were measured at NOA’s actinometric platform in Athens, Greece (Thissio site: 23.7°E, 37.6°N) by a CIMEL sun-photometer, and are analyzed in the context of this study. Measurements from a lidar ceilometer, satellite images, and back-trajectories are also used to identify the origin of aerosols during the smoke, but also combined dust and smoke events in low-aerosol days in the same month. Spectral measurements of the direct and diffuse solar irradiance from the Precision Solar Spectroradiometer (PSR) and measurements of the global and diffuse irradiance from precision pyranometers were also available in Athens, used to investigate the effects of different aerosol types on the levels of surface solar radiation measured. Furthermore, the efficiency of the nowcasting and forecasting tool nextSENSE, used to simulate and predict the levels of surface solar radiation, has been evaluated under such conditions.

Acknowledgements

This study was funded by the EuroGEO e-shape (grant agreement No 820852) and the H.F.R.I. National Research Project ASPIRE (project number 300).

How to cite: Fountoulakis, I., Raptis, I.-P., Kouklaki, D., Kosmopoulos, P., Psiloglou, B., Eleftheratos, K., and Kazadzis, S.: Spectral optical properties of aerosols in Athens, Greece during the August 2021 wildfires and their effects on surface solar radiation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2721, https://doi.org/10.5194/egusphere-egu22-2721, 2022.