scholarly journals Vertical variability of the properties of highly aged biomass burning aerosol transported over the southeast Atlantic during CLARIFY-2017

2020 ◽  
Vol 20 (21) ◽  
pp. 12697-12719 ◽  
Author(s):  
Huihui Wu ◽  
Jonathan W. Taylor ◽  
Kate Szpek ◽  
Justin M. Langridge ◽  
Paul I. Williams ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Climate Models ◽  
Marine Boundary Layer ◽  
Regional Climate ◽  
Single Scattering ◽  
Important Region ◽  
The Impact ◽  
Vertical Variability

Abstract. Seasonal biomass burning (BB) from June to October in central and southern Africa leads to absorbing aerosols being transported over the South Atlantic Ocean every year and contributes significantly to the regional climate forcing. The vertical distribution of submicron aerosols and their properties were characterized over the remote southeast Atlantic, using airborne in situ measurements made during the CLoud-Aerosol-Radiation Interactions and Forcing for Year 2017 (CLARIFY-2017) campaign. BB aerosols emitted from flaming-controlled fires were intensively observed in the region surrounding Ascension Island, in the marine boundary layer (MBL) and free troposphere (FT) up to 5 km. We show that the aerosols had undergone a significant ageing process during > 7 d transit from source, as indicated by the highly oxidized organic aerosol. The highly aged BB aerosols in the far-field CLARIFY region were also especially rich in black carbon (BC), with relatively low single-scattering albedos (SSAs), compared with those from other BB transported regions. The column-weighted dry SSAs during CLARIFY were observed to be 0.85, 0.84 and 0.83 at 405, 550 and 658 nm respectively. We also found significant vertical variation in the dry SSA, as a function of relative chemical composition and size. The lowest SSA in the column was generally in the low FT layer around 2000 m altitude (averages: 0.82, 0.81 and 0.79 at 405, 550 and 658 nm). This finding is important since it means that BB aerosols across the southeast Atlantic region are more absorbing than currently represented in climate models, implying that the radiative forcing from BB may be more strongly positive than previously thought. Furthermore, in the FT, average SSAs at 405, 550 and 658 nm increased to 0.87, 0.86 and 0.85 with altitude up to 5 km. This was associated with an enhanced inorganic nitrate mass fraction and aerosol size, likely resulting from increased partitioning of ammonium nitrate to the existing particles at higher altitude with lower temperature and higher relative humidity. After entrainment into the boundary layer (BL), aerosols were generally smaller in dry size than in the FT and had a larger fraction of scattering material with resultant higher average dry SSA, mostly due to marine emissions and aerosol removal by drizzle. In the BL, the SSA decreased from the surface to the BL top, with the highest SSA in the column observed near the surface. Our results provide unique observational constraints on aerosol parameterizations used in modelling regional radiation interactions over this important region. We recommend that future work should consider the impact of this vertical variability on climate models.

scholarly journals Vertical variability of the properties of highly aged biomass burning aerosol transported over the southeast Atlantic during CLARIFY-2017

2020 ◽  
Author(s):  
Huihui Wu ◽  
Jonathan W. Taylor ◽  
Kate Szpek ◽  
Justin Langridge ◽  
Paul I. Williams ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Climate Models ◽  
Marine Boundary Layer ◽  
Regional Climate ◽  
Single Scattering ◽  
Important Region ◽  
Absorbing Aerosols ◽  
Lower Temperature ◽  
The Impact ◽  
Vertical Variability

Abstract. Seasonal biomass burning (BB) from June to October in central and southern Africa leads to absorbing aerosols being transported over the south Atlantic Ocean every year, and contributes significantly to the regional climate forcing. The vertical distribution of submicron aerosols and their properties were characterized over the remote southeast Atlantic for the first time, using airborne in-situ measurements made during the CLoud-Aerosol-Radiation Interactions and Forcing for Year 2017 (CLARIFY-2017) campaign. BB aerosols were intensively observed in the region surrounding Ascension Island, in the marine boundary layer (MBL) and free troposphere (FT) up to 5 km. We show that the aerosols had undergone a significant aging process during > 7 days transit from source, as indicated by highly oxidized organic aerosol and thickly coated black carbon (BC). The highly aged BB aerosols in the CLARIFY region were also especially rich in BC compared with those from other regions. We also found significant vertical variation in the single scattering albedos (SSA) of these aerosols, as a function of relative chemical composition and size. The lowest SSA was generally in the low FT layer around 2000 m altitude (medians: 0.83 at 405 nm and 0.80 at 658 nm). This finding is important since it means that BB aerosols across the east Atlantic region are more absorbing than is currently represented in climate models. Furthermore, in the FT, we show that SSA increased with altitude and this was associated with an enhanced inorganic nitrate mass fraction and aerosol size. This likely results from increased partitioning to the existing particles at higher altitude with lower temperature and higher relative humidity. After entrainment into the BL, aerosols were generally smaller in size than were observed in the FT, and had a larger fraction of scattering material with resultant higher average dry SSA, mostly due to marine emissions and aerosol removal by drizzle. Our results provide unique observational constraints on aerosol parameterizations used in modelling regional radiation interactions over this important region. We recommend that future work should consider the impact of this vertical variability on climate models.

scholarly journals Direct and semi-direct radiative forcing of biomass-burning aerosols over the southeast Atlantic (SEA) and its sensitivity to absorbing properties: a regional climate modeling study

2020 ◽  
Vol 20 (21) ◽  
pp. 13191-13216
Author(s):  
Marc Mallet ◽  
Fabien Solmon ◽  
Pierre Nabat ◽  
Nellie Elguindi ◽  
Fabien Waquet ◽  
...  
Keyword(s):  
Air Temperature ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Climate Models ◽  
Regional Climate ◽  
Lower Troposphere ◽  
Regional Climate Models ◽  
Temperature Limit ◽  
Radiative Heating ◽  
Radiative Effects

Abstract. Simulations are performed for the period 2000–2015 by two different regional climate models, ALADIN and RegCM, to quantify the direct and semi-direct radiative effects of biomass-burning aerosols (BBAs) in the southeast Atlantic (SEA) region. Different simulations have been performed using strongly absorbing BBAs in accordance with recent in situ observations over the SEA. For the July–August–September (JAS) season, the single scattering albedo (SSA) and total aerosol optical depth (AOD) simulated by the ALADIN and RegCM models are consistent with the MACv2 climatology and MERRA-2 and CAMS-RA reanalyses near the biomass-burning emission sources. However, the above-cloud AOD is slightly underestimated compared to satellite (MODIS and POLDER) data during the transport over the SEA. The direct radiative effect exerted at the continental and oceanic surfaces by BBAs is significant in both models and the radiative effects at the top of the atmosphere indicate a remarkable regional contrast over SEA (in all-sky conditions), with a cooling (warming) north (south) of 10 ∘S, which is in agreement with the recent MACv2 climatology. In addition, the two models indicate that BBAs are responsible for an important shortwave radiative heating of ∼0.5–1 K per day over SEA during JAS with maxima between 2 and 4 km a.m.s.l. (above mean sea level). At these altitudes, BBAs increase air temperature by ∼0.2–0.5 K, with the highest values being co-located with low stratocumulus clouds. Vertical changes in air temperature limit the subsidence of air mass over SEA, creating a cyclonic anomaly. The opposite effect is simulated over the continent due to the increase in lower troposphere stability. The BBA semi-direct effect on the lower troposphere circulation is found to be consistent between the two models. Changes in the cloud fraction are moderate in response to the presence of smoke, and the models differ over the Gulf of Guinea. Finally, the results indicate an important sensitivity of the direct and semi-direct effects to the absorbing properties of BBAs. Over the stratocumulus (Sc) region, DRE varies from +0.94 W m−2 (scattering BBAs) to +3.93 W m−2 (most absorbing BBAs).

scholarly journals Isotopic constraints on the role of hypohalous acids in sulfate aerosol formation in the remote marine boundary layer

2016 ◽  
Author(s):  
Qianjie Chen ◽  
Lei Geng ◽  
Johan A. Schmidt ◽  
Zhouqing Xie ◽  
Hui Kang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Marine Boundary Layer ◽  
Reaction Rates ◽  
Sulfate Aerosol ◽  
Aerosol Formation ◽  
Sulfate Production ◽  
Hypohalous Acids

Abstract. Sulfate is an important component of global atmospheric aerosol, and has partially compensated for greenhouse gas-induced warming during the industrial period. The magnitude of direct and indirect radiative forcing of aerosols since preindustrial time is a large uncertainty in climate models, which has been attributed largely to uncertainties in the preindustrial environment. Here, we report observations of the oxygen isotopic composition (Δ17O) of sulfate aerosol collected in the remote marine boundary layer (MBL) in spring and summer in order to evaluate sulfate production mechanisms in pristine-like environments. Model-aided analysis of the observations suggests that 33–50 % of sulfate in the MBL is formed via oxidation by hypohalous acids (HOX = HOBr + HOCl), a production mechanism typically excluded in large scale models due to uncertainties in the reaction rates. Based on the estimated fraction of sulfate formed via HOX oxidation, we further estimate that daily-averaged HOX concentrations on the order of 0.01–0.1 parts per trillion (ppt = pmol / mol) in the remote MBL during spring and summer are sufficient to explain the observations.

scholarly journals Evaluation of climate model aerosol seasonal and spatial variability over Africa using AERONET

2017 ◽  
Vol 17 (22) ◽  
pp. 13999-14023 ◽  
Author(s):  
Hannah M. Horowitz ◽  
Rebecca M. Garland ◽  
Marcus Thatcher ◽  
Willem A. Landman ◽  
Zane Dedekind ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Aerosol Particles ◽  
Atmospheric Model ◽  
Model Aerosol ◽  
The Impact

Abstract. The sensitivity of climate models to the characterization of African aerosol particles is poorly understood. Africa is a major source of dust and biomass burning aerosols and this represents an important research gap in understanding the impact of aerosols on radiative forcing of the climate system. Here we evaluate the current representation of aerosol particles in the Conformal Cubic Atmospheric Model (CCAM) with ground-based remote retrievals across Africa, and additionally provide an analysis of observed aerosol optical depth at 550 nm (AOD550 nm) and Ångström exponent data from 34 Aerosol Robotic Network (AERONET) sites. Analysis of the 34 long-term AERONET sites confirms the importance of dust and biomass burning emissions to the seasonal cycle and magnitude of AOD550 nm across the continent and the transport of these emissions to regions outside of the continent. In general, CCAM captures the seasonality of the AERONET data across the continent. The magnitude of modeled and observed multiyear monthly average AOD550 nm overlap within ±1 standard deviation of each other for at least 7 months at all sites except the Réunion St Denis Island site (Réunion St. Denis). The timing of modeled peak AOD550 nm in southern Africa occurs 1 month prior to the observed peak, which does not align with the timing of maximum fire counts in the region. For the western and northern African sites, it is evident that CCAM currently overestimates dust in some regions while others (e.g., the Arabian Peninsula) are better characterized. This may be due to overestimated dust lifetime, or that the characterization of the soil for these areas needs to be updated with local information. The CCAM simulated AOD550 nm for the global domain is within the spread of previously published results from CMIP5 and AeroCom experiments for black carbon, organic carbon, and sulfate aerosols. The model's performance provides confidence for using the model to estimate large-scale regional impacts of African aerosols on radiative forcing, but local feedbacks between dust aerosols and climate over northern Africa and the Mediterranean may be overestimated.

scholarly journals Isotopic constraints on the role of hypohalous acids in sulfate aerosol formation in the remote marine boundary layer

2016 ◽  
Vol 16 (17) ◽  
pp. 11433-11450 ◽  
Author(s):  
Qianjie Chen ◽  
Lei Geng ◽  
Johan A. Schmidt ◽  
Zhouqing Xie ◽  
Hui Kang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Marine Boundary Layer ◽  
Reaction Rates ◽  
Sulfate Aerosol ◽  
Aerosol Formation ◽  
Sulfate Production ◽  
Hypohalous Acids

Abstract. Sulfate is an important component of global atmospheric aerosol, and has partially compensated for greenhouse gas-induced warming during the industrial period. The magnitude of direct and indirect radiative forcing of aerosols since preindustrial times is a large uncertainty in climate models, which has been attributed largely to uncertainties in the preindustrial environment. Here, we report observations of the oxygen isotopic composition (Δ17O) of sulfate aerosol collected in the remote marine boundary layer (MBL) in spring and summer in order to evaluate sulfate production mechanisms in pristine-like environments. Model-aided analysis of the observations suggests that 33–50 % of sulfate in the MBL is formed via oxidation by hypohalous acids (HOX  =  HOBr + HOCl), a production mechanism typically excluded in large-scale models due to uncertainties in the reaction rates, which are due mainly to uncertainties in reactive halogen concentrations. Based on the estimated fraction of sulfate formed via HOX oxidation, we further estimate that daily-averaged HOX mixing ratios on the order of 0.01–0.1 parts per trillion (ppt  =  pmol/mol) in the remote MBL during spring and summer are sufficient to explain the observations.

scholarly journals Understanding the seasonality and climatology of aerosols in Africa through evaluation of CCAM aerosol simulations against AERONET measurements

2017 ◽  
Author(s):  
Hannah M. Horowitz ◽  
Rebecca M. Garland ◽  
Marcus Thatcher ◽  
Willem A. Landman ◽  
Zane Dedekind ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Aerosol Particles ◽  
Atmospheric Model ◽  
Reunion Island ◽  
Réunion Island ◽  
The Impact

Abstract. The sensitivity of climate models to the characterization of African aerosol particles is poorly understood. Africa is a major source of dust and biomass burning aerosols and so this represents an important research gap in understanding the impact of aerosols on radiative forcing of the climate system. Here we evaluate the current representation of aerosol particles in the Conformal Cubic Atmospheric Model (CCAM) with ground-based observations across Africa, and additionally provide an analysis of aerosol optical depth at 550 nm (AOD550nm) and Ångström exponent data from thirty-four Aerosol Robotic Network (AERONET) sites. Analysis of the 34 long-term AERONET sites confirms the importance of dust and biomass burning emissions to the seasonal cycle and magnitude of AOD550nm across the continent and the transport of these emissions to regions outside of the continent. Western African sites had the largest AOD550nm values, on average, with the timing and magnitude of AOD550nm maxima dominated by desert dust. The impact of dust on aerosol loading is also apparent at northern African sites, with peak AOD550nm occurring later than the western sites. The seasonal variation in the location of the intertropical convergence zone and associated northward shift in dust transport may be responsible for the shift in timing of maximum AOD550nm between the western and northern African sites. Southern African sites have the lowest AOD550nm values on average, and peak during the biomass burning period. The outflow of these aerosol particles was observed at Ascension Island and Reunion Island AERONET stations. In general, CCAM captures well the seasonality of the AERONET data across the continent. The magnitude of modeled and observed multi-year monthly average AOD550nm overlap within ±1 standard deviation of each other for at least 7 months at all sites except Reunion Island. The timing of peak AOD550nm in southern Africa in the model occurs one month prior to the observed peak, which does not align with the timing of maximum fire counts in the region. For the western and northern African sites, it is evident that CCAM currently overestimates dust in some regions while others (e.g., the Arabian Peninsula) are better characterized. This may be due to overestimated dust lifetime, or that the characterization of the soil for these areas needs to be updated with local information. The CCAM simulated AOD550nm for the global domain is within the spread of previously published results from CMIP5 and AeroCom experiments for black carbon, organic carbon and sulfate aerosols. The model’s performance provides confidence for using the model to estimate large-scale regional impacts of African aerosols on radiative forcing, but local feedbacks between dust aerosols and climate over northern Africa and the Mediterranean may be overestimated.

scholarly journals Direct and semi-direct radiative forcing of biomass burning aerosols over the Southeast Atlantic (SEA) and its sensitivity to absorbing properties: a regional climate modeling study

2020 ◽  
Author(s):  
Marc Mallet ◽  
Fabien Solmon ◽  
Pierre Nabat ◽  
Nellie Elguindi ◽  
Fabien Waquet ◽  
...  
Keyword(s):  
Air Temperature ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Climate Models ◽  
Regional Climate ◽  
Lower Troposphere ◽  
Regional Climate Models ◽  
Temperature Limit ◽  
Radiative Heating ◽  
Radiative Effects

Abstract. Simulations are performed for the period 2000–2015 by two different regional climate models, ALADIN–Climat and RegCM, to quantify the direct and semi-direct radiative effects of biomass burning aerosols (BBA) in the Southeast Atlantic (SEA) region. The approach of using two different independent RCMs reinforces the robustness of the results. Different simulations have been performed using strongly absorbing BBA in accordance with recent in situ observations over the SEA. For the July–August–September (JAS) season, the single scattering albedo (SSA) and total aerosol optical depth (AOD) simulated by the ALADIN–Climat and RegCM models are consistent with the MACv2 climatology and MERRA-2 and CAMS-RA reanalyses near the biomass burning emission sources. However, the above-cloud AOD is slightly underestimated compared to satellite (MODIS and POLDER) data during the transport over the SEA. The direct radiative effect exerted at the continental and oceanic surfaces by BBA is significant in both models and the radiative effects at the top of the atmosphere indicate a remarkable regional contrast over SEA (in all-sky conditions), with a cooling (warming) north (south) of 10° S, which is in agreement with the recent MACv2 climatology. In addition, the two models indicate that BBA are responsible for an important shortwave radiative heating of ~ 0.5–1 K per day over SEA during JAS with maxima between 2 and 4 km above mean sea-level. At these altitudes, BBA increase air temperature by ~ 0.2–0.5 K, with the highest values being co-located with low stratocumulus clouds. Vertical changes in air temperature limit the subsidence over SEA creating a cyclonic anomaly. The opposite effect is simulated over the continent due to the increase in lower troposphere stability. The BBA semi-direct effect on the lower troposphere circulation is found to be consistent between the two models. Changes in the cloud fraction are moderate in response to the presence of smoke and the models differ over the Gulf of Guinea. Finally, the results indicate an important sensitivity of the direct and semi-direct effects to the absorbing properties of BBA.

scholarly journals On the Use of Original and Bias-Corrected Climate Simulations in Regional-Scale Hydrological Scenarios in the Mediterranean Basin

Atmosphere ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 799 ◽  
Author(s):  
Lorenzo Sangelantoni ◽  
Barbara Tomassetti ◽  
Valentina Colaiuda ◽  
Annalina Lombardi ◽  
Marco Verdecchia ◽  
...  
Keyword(s):  
Climate Change ◽  
Radiative Forcing ◽  
Climate Models ◽  
Regional Climate ◽  
Regional Scale ◽  
Central Italy ◽  
Stress Index ◽  
Climate Change Signal ◽  
Correction Technique ◽  
The Impact

The response of Mediterranean small catchments hydrology to climate change is still relatively unexplored. Regional Climate Models (RCMs) are an established tool for evaluating the expected climate change impact on hydrology. Due to the relatively low resolution and systematic errors, RCM outputs are routinely and statistically post-processed before being used in impact studies. Nevertheless, these techniques can impact the original simulated trends and then impact model results. In this work, we characterize future changes of a small Apennines (Central Italy) catchment hydrology, according to two radiative forcing scenarios (Representative Concentration Pathways, RCPs, 4.5 and 8.5). We also investigate the impact of a widely used bias correction technique, the empirical Quantile Mapping (QM) on the original Climate Change Signal (CCS), and the subsequent alteration of the original Hydrological Change Signal (HCS). Original and bias-corrected simulations of five RCMs from Euro-CORDEX are used to drive the CETEMPS hydrological model CHyM. HCS is assessed by using monthly mean discharge and a hydrological-stress index. HCS shows a large spatial and seasonal variability where the summer results are affected by the largest decrease of mean discharge (down to −50%). QM produces a small alteration of the original CCS, which generates a generally wetter HCS, especially during the spring season.

Monitoring of long-range transported smoke in polar regions with remote sensing instruments

2021 ◽  
Author(s):  
Ramiro González Catón ◽  
Carlos Toledano ◽  
Roberto Román Diez ◽  
David Mateos ◽  
Eija Asmi ◽  
...  
Keyword(s):  
Particle Size ◽  
Long Range ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Single Scattering ◽  
The Arctic ◽  
Polar Regions ◽  
Intergovernmental Panel ◽  
Radiative Balance ◽  
The Impact

<p><span><span>Long range transported aerosol from biomass burning affects polar regions, especially the Arctic. The frequency and intensity of bushfires in the context of a warming climate has been pointed out in the last report of the Intergovernmental Panel on Climate Change. In high latitudes, these events impact large areas through long-range transport of the smoke particles in the troposphere or even the stratosphere. The lifetime and radiative impact are related with the height of the plumes and the processes that modify particle size and absorptive properties during the transport. Several recent publications have shown the impact of the Australian smoke in the southern hemisphere, including Antarctica, in January-March 2020. The tools that were used to monitor that extraordinary event can be used in the Arctic to investigate similar effects in the frequent biomass burning events that generate smoke plumes in boreal regions. In this work, we present the results derived from ground-based instrumentation as well as satellite and model data. The change of the smoke properties after several days of transport is also provided, namely an increase in the fine mode particle size and the single scattering albedo, as well as a decrease in the coarse mode particle concentration. These features are relevant for radiative forcing calculations and therefore the impact of long range transported smoke in the radiative balance over polar regions.</span></span></p>

scholarly journals Effect of biomass burning on marine stratocumulus clouds off the California coast

2009 ◽  
Vol 9 (22) ◽  
pp. 8841-8856 ◽  
Author(s):  
J. Brioude ◽  
O. R. Cooper ◽  
G. Feingold ◽  
M. Trainer ◽  
S. R. Freitas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Cloud Fraction ◽  
Marine Stratocumulus ◽  
Cloud Albedo ◽  
Stratocumulus Clouds ◽  
Absorbing Aerosols ◽  
Indirect Radiative Forcing

Abstract. Aerosol-cloud interactions are considered to be one of the most important and least known forcings in the climate system. Biomass burning aerosols are of special interest due to their radiative impact (direct and indirect effect) and their potential to increase in the future due to climate change. Combining data from Geostationary Operational Environmental Satellite (GOES) and MODerate-resolution Imaging Spectroradiometer (MODIS) with passive tracers from the FLEXPART Lagrangian Particle Dispersion Model, the impact of biomass burning aerosols on marine stratocumulus clouds has been examined in June and July of 2006–2008 off the California coast. Using a continental tracer, the indirect effect of biomass burning aerosols has been isolated by comparing the average cloud fraction and cloud albedo for different meteorological situations, and for clean versus polluted (in terms of biomass burning) continental air masses at 14:00 local time. Within a 500 km-wide band along the coast of California, biomass burning aerosols, which tend to reside above the marine boundary layer, increased the cloud fraction by 0.143, and the cloud albedo by 0.038. Absorbing aerosols located above the marine boundary layer lead to an increase of the lower tropospheric stability and a reduction in the vertical entrainment of dry air from above, leading to increased cloud formation. The combined effect was an indirect radiative forcing of −7.5% ±1.7% (cooling effect) of the outgoing radiative flux at the top of the atmosphere on average, with a bias due to meteorology of +0.9%. Further away from the coast, the biomass burning aerosols, which were located within the boundary layer, reduced the cloud fraction by 0.023 and the cloud albedo by 0.006, resulting in an indirect radiative forcing of +1.3% ±0.3% (warming effect) with a bias of +0.5%. These results underscore the dual role that absorbing aerosols play in cloud radiative forcing.

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