We have developed detailed emission inventories for the amount of both black and organic carbon particles from biomass burning sources (wood fuel, charcoal burning, dung, charcoal production, ...agricultural, savanna and forest fires). We have also estimated an inventory for organic carbon particles from fossil fuel burning and urban activities from an existing inventory for fossil fuel sources of black carbon. We also provide an estimate for the natural source of organic matter. These emissions have been used together with our global aerosol model to study the global distribution of carbonaceous aerosols. The accuracy of the inventories and the model formulation has been tested by comparing the model simulations of carbonaceous aerosols in the atmosphere and in precipitation with observations reported in the literature. For most locations and seasons, the predicted concentrations are in reasonable agreement with the observations, although the model underpredicts black carbon concentrations in polar regions. The predicted concentrations in remote areas are extremely sensitive to both the rate of removal by wet deposition and the height of injection of the aerosols. Finally, a global map of the aerosol single scattering albedo was developed from the simulated carbonaceous particle distribution and a previously developed model for aerosol sulfates. The computed aerosol single scattering albedos compare well with observations, suggesting that most of the important aerosol species have been included in the model. For most locations and seasons, the single scattering albedo is larger than 0.85, indicating that these aerosols, in general, lead to a net cooling.
Within the African Monsoon Multidisciplinary Analysis (AMMA), we investigate the impact of nitrogen oxides produced by lightning (LiNOx ) and convective transport during the West African Monsoon ...(WAM) upon the composition of the upper troposphere (UT) in the tropics. For this purpose, we have performed simulations with 4 state-of-the-art chemistry transport models involved within AMMA, namely MOCAGE, TM4, LMDz-INCA and p-TOMCAT. The model intercomparison is complemented with an evaluation of the simulations based on both spaceborne and airborne observations. The baseline simulations show important differences between the UT CO and O3 distributions simulated by each of the 4 models when compared to measurements from the MOZAIC program and fom the Aura/MLS spaceborne sensor. We show that such model discrepancies can be explained by differences in the convective transport parameterizations and, more particularly, the altitude reached by convective updrafts (ranging between ~200-125 hPa). Concerning UT O3 , the models exhibit a good agreement with the main observed features. Nevertheless the majority of models simulate low O3 concentrations compared to both MOZAIC and Aura/MLS observations south of the equator, and rather high concentrations in the Northern Hemisphere. Sensitivity studies are performed to quantify the effect of deep convective transport and the influence of LiNOx production on the UT composition. These clearly indicate that the CO maxima and the elevated O3 concentrations south of the equator are due to convective uplift of air masses impacted by Southern African biomass burning, in agreement with previous studies. Moreover, during the WAM, LiNOx from Africa are responsible for the highest UT O3 enhancements (10-20 ppbv) over the tropical Atlantic between 10° S-20° N. Differences between models are primarily due to the performance of the parameterizations used to simulate lightning activity which are evaluated using spaceborne observations of flash frequency. Combined with comparisons of in-situ NO measurements we show that the models producing the highest amounts of LiNOx over Africa during the WAM (INCA and p-TOMCAT) capture observed NO profiles with the best accuracy, although they both overestimate lightning activity over the Sahel.
Pollutant plumes with enhanced concentrations of trace gases and aerosols were observed over the southern coast of West Africa during August 2006 as part of the AMMA wet season field campaign. Plumes ...were observed both in the mid and upper troposphere. In this study we examined the origin of these pollutant plumes, and their potential to photochemically produce ozone (O3) downwind over the Atlantic Ocean. Their possible contribution to the Atlantic O3 maximum is also discussed. Runs using the BOLAM mesoscale model including biomass burning carbon monoxide (CO) tracers were used to confirm an origin from central African biomass burning fires. The plumes measured in the mid troposphere (MT) had significantly higher pollutant concentrations over West Africa compared to the upper tropospheric (UT) plume. The mesoscale model reproduces these differences and the two different pathways for the plumes at different altitudes: transport to the north-east of the fire region, moist convective uplift and transport to West Africa for the upper tropospheric plume versus north-west transport over the Gulf of Guinea for the mid-tropospheric plume. Lower concentrations in the upper troposphere are mainly due to enhanced mixing during upward transport. Model simulations suggest that MT and UT plumes are 16 and 14 days old respectively when measured over West Africa. The ratio of tracer concentrations at 600 hPa and 250 hPa was estimated for 14–15 August in the region of the observed plumes and compares well with the same ratio derived from observed carbon dioxide (CO2) enhancements in both plumes. It is estimated that, for the period 1–15 August, the ratio of Biomass Burning (BB) tracer concentration transported in the UT to the ones transported in the MT is 0.6 over West Africa and the equatorial South Atlantic. Runs using a photochemical trajectory model, CiTTyCAT, initialized with the observations, were used to estimate in-situ net photochemical O3 production rates in these plumes during transport downwind of West Africa. The mid-troposphere plume spreads over altitude between 1.5 and 6 km over the Atlantic Ocean. Even though the plume was old, it was still very photochemically active (mean net O3 production rates over 10 days of 2.6 ppbv/day and up to 7 ppbv/day during the first days) above 3 km especially during the first few days of transport westward. It is also shown that the impact of high aerosol loads in the MT plume on photolysis rates serves to delay the peak in modelled O3 concentrations. These results suggest that a significant fraction of enhanced O3 in mid-troposphere over the Atlantic comes from BB sources during the summer monsoon period. According to simulated occurrence of such transport, BB may be the main source for O3 enhancement in the equatorial south Atlantic MT, at least in August 2006. The upper tropospheric plume was also still photochemically active, although mean net O3 production rates were slower (1.3 ppbv/day). The results suggest that, whilst the transport of BB pollutants to the UT is variable (as shown by the mesoscale model simulations), pollution from biomass burning can make an important contribution to additional photochemical production of O3 in addition to other important sources such as nitrogen oxides (NOx) from lightning.
We present a model simulation for the year 1995 accounting for primary particles, which are an important component of fine aerosols over Europe. A new emission inventory for black carbon (BC) was ...developed on the basis of the recent European emission inventory of anthropogenic primary particulate matter (Coordinated European Programme on Particulate Matter Emission Inventories, Projections and Guidance (CEPMEIP)). The annual BC emissions of Europe and the former Soviet Union for 1995 are estimated at 0.47 and 0.26 Tg C, respectively, with highest contributions from transport (off‐road and on‐road) and households. Modeled BC concentrations range from ≤0.05 μg/m3 in remote regions to more than 1 μg/m3 over densely populated areas. The modeled BC concentration is about 25% of the total primary aerosol concentration. The primary aerosol fields were combined with previously calculated secondary aerosol concentrations to obtain an estimate of the total anthropogenic fine aerosol distribution. Modeled BC levels contribute only 4–10% to fine aerosol mass, whereas sulphate and nitrate contribute 25–50 and 5–35%, respectively. Comparison with experimental data revealed that the model underestimates PM2.5 levels, mostly caused by the underprediction of total carbonaceous material (BC and OC) by a factor of ∼2. The underestimation can partly be explained by the influence of local emissions, measurement uncertainties, natural sources, and representation of wet deposition. However, the uncertainties associated with the emission inventory for BC (and total PM) may be the most important cause for the discrepancy. In comparison with previous studies, our BC emission estimate is a factor of 2 lower, caused by the choice of more recent emission factors. Therefore a better knowledge of emission factors is urgently needed to estimate the BC (and PM) emissions reliably.
One of the main uncertainties in the estimation of the climatic impact of aerosols is linked to our knowledge of gas and aerosol emissions. This is particularly crucial over Asia, where a strong ...regional fingerprint is observed, with different emission types, depending on the various vegetation and climate conditions (biomass burning emissions) and on the very fast changes of the population and industrialization (biofuel and fossil fuel emissions). The main contribution of this work is to derive a biomass burning inventory of 1° × 1° over Asia (the Asian biomass burning inventory (ABBI)) for gases and particles for the Aerosol Characterization Experiment‐Asia (ACE‐Asia) and Transport and Chemical Evolution Over the Pacific (TRACE‐P) campaign period (March to May 2001) in 2001. In this paper we apply new estimates of burnt biomass area to estimate emissions. The method is based on burnt areas (GBA2000 project; Tansey et al. (2002) and Grégoire et al. (2003)) obtained from 1 km resolution SPOT‐VEGETATION satellite data. Regional‐scale maps of burnt areas are produced, and then spatial and temporal emission distribution are obtained from biomass density and emission factors. Strength and weaknesses associated with the use of satellite products are discussed, including the problem of subpixel classification and the lack of validation data for the accuracy assessment of the products for the studied area. Estimated emissions are compared with ACE‐Asia and TRACE‐P Modeling and Emission Support System (ACESS) climatological estimates. In addition, interannual variability is estimated by preparing inventories for the years 2000 and 2001.
A global chemistry-climate model LMDz_INCA is used to investigate the contribution of African and Asian emissions to tropospheric ozone over Central and West Africa during the summer monsoon. The ...model results show that ozone in this region is most sensitive to lightning NOx and to Central African biomass burning emissions. However, other emission categories also contribute significantly to regional ozone. The maximum ozone changes due to lightning NOx occur in the upper troposphere between 400 hPa and 200 hPa over West Africa and downwind over the Atlantic Ocean. Biomass burning emissions mainly influence ozone in the lower and middle troposphere over Central Africa, and downwind due to westward transport. Biogenic emissions of volatile organic compounds, which can be uplifted from the lower troposphere to higher altitudes by the deep convection that occurs over West Africa during the monsoon season, lead to maximum ozone changes in the lower stratosphere region. Soil NOx emissions over the Sahel region make a significant contribution to ozone in the lower troposphere. In addition, convective uplift of these emissions and subsequent ozone production are also an important source of ozone in the upper troposphere over West Africa. Concerning African anthropogenic emissions, they only make a small contribution to ozone compared to the other emission categories. The model results indicate that most ozone changes due to African emissions occur downwind, especially over the Atlantic Ocean, far from the emission regions. The import of Asian emissions also makes a considerable contribution to ozone concentrations above 150 hPa and has to be taken into account in studies of the ozone budget over Africa. Using IPCC AR5 (Intergovernmental Panel on Climate Change; Fifth Assessment Report) estimates of anthropogenic emissions for 2030 over Africa and Asia, model calculations show larger changes in ozone over Africa due to growth in Asian emissions compared to African emissions over the next 20 yr.
The aim of this study is to present the organic and inorganic spectral aerosol module-radiative (ORISAM-RAD) module, allowing the 3D distribution of aerosol radiative properties (aerosol optical ...depth, single scattering albedo and asymmetry parameter) from the ORISAM module. In this work, we test ORISAM-RAD for one selected day (24th June) during the ESCOMPTE (expérience sur site pour contraindre les modèles de pollution atmosphérique et de transport d’emissions) experiment for an urban/industrial aerosol type. The particle radiative properties obtained from in situ and AERONET observations are used to validate our simulations. In a first time, simulations obtained from ORISAM-RAD indicate high aerosol optical depth (AOD)∼0.50–0.70±0.02 (at 440
nm) in the aerosol pollution plume, slightly lower (∼10–20%) than AERONET retrievals. In a second time, simulations of the single scattering albedo (
ω
o) have been found to well reproduce the high spatial heterogeneities observed over this domain. Concerning the asymmetry parameter (
g), ORISAM-RAD simulations reveal quite uniform values over the whole ESCOMPTE domain, comprised between 0.61±0.01 and 0.65±0.01 (at 440
nm), in excellent agreement with ground based in situ measurements and AERONET retrievals. Finally, the outputs of ORISAM-RAD have been used in a radiative transfer model in order to simulate the diurnal direct radiative forcing at different locations (urban, industrial and rural). We show that anthropogenic aerosols strongly decrease surface solar radiation, with diurnal mean surface forcings comprised between −29.0±2.9 and −38.6±3.9
W
m
−2, depending on the sites. This decrease is due to the reflection of solar radiations back to space (−7.3±0.8<Δ
F
TOA<−12.3±1.2
W
m
−2) and to its absorption into the aerosol layer (21.1±2.1<Δ
F
ATM<26.3±2.6
W
m
−2). These values are found to be consistent with those measured at local scale.
An atmospheric year‐round study of C2–C5 dicarboxylic acids (oxalic, malonic, succinic, malic, and glutaric) and sulfate was conducted in 2002 and 2003 at three remote western Europe continental ...sites located at different elevations (from 630 to 4360 m asl). Whatever the site and the season, oxalic acid is always the dominant diacid (average 64% of total dicarboxylic acids) followed by malonic acid (15% of total dicarboxylic acids). High correlation coefficients are observed between C3 (malonic), C4 (malic and succinic), and C5 (glutaric) acids and oxalic acid. These strong relationships between C2–C5 diacids support the hypothesis of a common production of these diacids through the aqueous phase chemistry of glutaric acid. Data gained at different elevations are here useful to compare the mass formation rates of sulfate and dicarboxylic acids. It is shown that in summer the decrease of the sum of dicarboxylic acids with height is far less pronounced than the decrease of sulfate (a factor of 2 instead of 6.8 from 630 to 4360 m asl). That demonstrates that the production of dicarboxylic acids occurs at up to 4300 m elevation while the production of sulfate from SO2 mainly takes place between the boundary layer and 3000 m elevation. With respect to summer 2002 the sum of dicarboxylic acids was enhanced in summer 2003 (from 136 to 331 ng m−3 STP at 2870 m asl, for instance) whereas a weaker increase is observed for sulfate (from 1700 to 2500 ng m−3 STP at 2870 m asl). These changes are attributed to the particular summer 2003 conditions which led to enhanced level of oxidants (strengthened secondary productions) and warmer temperatures (enhanced emissions of biogenic precursors of diacids).
Southern West Africa (SWA) is influenced by large numbers of aerosol particles of both anthropogenic and natural origins. Anthropogenic aerosol emissions are expected to increase in the future due to ...the economical growth of African megacities. In this paper, we investigate the aerosol optical depth (AOD) in the coastal area of the Gulf of Guinea using sun photometer and MODIS satellite observations. A network of lightweight handheld sun photometers have been deployed in SWA from December 2014 to April 2017 at five different locations in Côte d'Ivoire and Benin. The handheld sun photometer measures the solar irradiance at 465, 540 and 619 nm and is operated manually once per day. Handheld-sun-photometer observations are complemented by available AERONET sun photometer observations and MODIS level 3 time series between 2003 and 2019. MODIS daily level 3 AOD agrees well with sun photometer observations in Abidjan and Cotonou (correlation coefficient R=0.89 and RMSE = 0.19). A classification based on the sun photometer AOD and Ångström exponent (AE) is used to separate the influence of coarse mineral dust and urban-like aerosols. The AOD seasonal pattern is similar for all the sites and is clearly influenced by the mineral dust advection from December to May. Sun photometer AODs are analyzed in coincidence with surfacePM2.5 concentrations to infer trends in the particulate pollution levels over conurbations of Abidjan (Côte d'Ivoire) and Cotonou (Benin). PM2.5-to-AOD conversion factors are evaluated as a function of the season and the aerosol type identified in the AE classification. The highest PM2.5 concentrations (up to 300 µgm-3) are associated with the advection of mineral dust in the heart of the dry season (December–February). Annual means are around 30 µgm-3, and 80 % of days in the winter dry season have a value above 35 µgm-3, while concentrations remain below 16 µgm-3 from May to September. No obvious trend is observed in the 2003–2019 MODIS-derived PM2.5 time series. However the short dry period (August–September), when urban-like aerosols dominate, is associated with a monotonic trend between 0.04 and 0.43 µgm-3yr-1 in the PM2.5 concentrations over the period 2003–2017. The monotonic trend remains uncertain but is coherent with the expected increase in combustion aerosol emissions in SWA.
An investigation of aerosol chemistry was carried out at Sevettijarvi in Finnish Lapland between September 1997 and June 1999. Aerosol particles were collected on a 2‐day basis using two‐stage ...virtual impactors and were analyzed with ion chromatography for major inorganic cations and anions and for a suite of organic acids. Aerosols were also sampled in parallel on a 4‐day basis for the analysis of organic carbon (OC) and black carbon (BC). The average total mass is about 3 μg m−3 and does not significantly vary according to the season or the type of air mass. The major chemical components are sulfate, sea salts, and organic carbon, which account together for more than 80% of the total aerosol mass. BC, ammonium, nitrate, methanesulfonic acid, and the estimated crustal fraction each accounts for a few percent at most in any situation. Non‐sea‐salt (nss) sulfate concentrations are maximum during late winter and spring, related to the Arctic haze, associated with increased concentrations in BC, ammonium, and nss K+. The organic fraction is at its lowest in winter, as are the concentrations of most organic acids. OC and short‐chain organic acid concentrations increase during springtime, which may be due to enhanced photochemistry at polar sunrise. The chemical profile is rather different during summer, with a strong decrease of the anthropogenic fraction and a larger occurrence of episodic marine events. However, the main characteristic is the very large increase in OC concentrations, which is the main component of the aerosol at that time and may be linked with local and regional enhanced biogenic activity. The aerosol at Sevettijarvi presents some specificity compared with other Arctic sites, with a much smaller impact of Arctic haze and marine events in winter and a much larger impact of biogenic sources in summer. The low contribution of the crustal fraction indicates low occurrences of transport of desert dust from Eurasia. The time series of concentrations indicate a large variability in the chemical profiles on short timescales, linked with changes in the origin of the air masses. It shows that even purely marine aerosol still comprises about 10% of nss sulfate associated with BC and OC. The profile in the continental case is largely dominated by nss sulfate, with strong increases in the ammonium and BC fractions.
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