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The 2020 COVID-19 crisis caused an unprecedented drop in anthropogenic emissions of air pollutants and greenhouse gases. Given that emissions estimates from official national inventories for the year 2020 were not reported until 2 years later, new and non-traditional datasets to estimate near-real-time emissions became particularly relevant and widely used in international monitoring and modelling activities during the pandemic. This study investigates the impact of the COVID-19 pandemic on 2020 European (the 27 EU member states and the UK) emissions by comparing a selection of such near-real-time emission estimates, with the official inventories that were subsequently reported in 2022 under the Convention on Long-Range Transboundary Air Pollution (CLRTAP) and the United Nations Framework Convention on Climate Change (UNFCCC). Results indicate that annual changes in total 2020 emissions reported by official and near-real-time estimates are fairly in line for most of the chemical species, with NOx and fossil fuel CO2 being reported as the ones that experienced the largest reduction in Europe in all cases. However, large discrepancies arise between the official and non-official datasets when comparing annual results at the sector and country level, indicating that caution should be exercised when estimating changes in emissions using specific near-real-time activity datasets, such as time mobility data derived from smartphones. The main examples of these differences are observed for the manufacturing industry NOx (relative changes ranging between −21.4 % and −5.4 %) and road transport CO2 (relative changes ranging between −29.3 % and −5.6 %) total European emissions. Additionally, significant discrepancies are observed between the quarterly and monthly distribution of emissions drops reported by the various near-real-time inventories, with differences of up to a factor of 1.5 for total NOx during April 2020, when restrictions were at their maximum. For residential combustion, shipping and the public energy industry, results indicate that changes in emissions that occurred between 2019 and 2020 were mainly dominated by non-COVID-19 factors, including meteorology, the implementation of the Global Sulphur Cap and the shutdown of coal-fired power plants as part of national decarbonization efforts, respectively. The potential increase in NMVOC emissions from the intensive use of personal protective equipment such as hand sanitizer gels is considered in a heterogeneous way across countries in officially reported inventories, indicating the need for some countries to base their calculations on more advanced methods. The findings of this study can be used to better understand the uncertainties in near-real-time emissions and how such emissions could be used in the future to provide timely updates to emission datasets that are critical for modelling and monitoring applications.

We present two inventories of anthropogenic emissions as well as an air quality atlas linked to Copernicus, the European earth observation system. CAMS-GLOB-ANTv5.3, a global anthropogenic emissions inventory, has been developed and provides emission data for the major atmospheric pollutants and greenhouse gases, as well as 25 speciated Volatile Organic Compounds (VOCs), for the period 2000-2023. This inventory is used as input for the Copernicus Atmosphere Monitoring System (CAMS) atmospheric reanalysis and forecasts.A mosaic inventory of anthropogenic emissions was also developed as part of the Copernicus CO2 project (CoCO2) focusing on greenhouse gases emissions. This mosaic uses the CAMS-GLOB-ANTv5.3 inventory as a global basis, and the DACCIWA2 (Dynamics-Aerosol-Chemistry-Cloud interactions in West Africa) inventory, a regional African emissions inventory. DACCIWA2 provides 0.1x0.1 degree resolution emissions of greenhouse gases and atmospheric pollutants for the period 2010-2018.The CAMS reanalysis is being used to develop an atlas of air quality called AQWA (Air Quality Worldwide Atlas). The AQWA atlas gives precious information about historical, climatological and current atmospheric composition, as well as air quality indexes. These statistics are available for all countries around the world, as well as states/provinces for the United States and China.This presentation describes the methodology used to develop and evaluate the two inventories and shows a few visualization examples from the atlas, which is still in development.

There are very few African regional inventories providing biofuel and fossil fuel emissions. Within the framework of the DACCIWA project, we have developed an African regional anthropogenic emission inventory including the main African polluting sources (wood and charcoal burning, charcoal making, trucks, cars, buses and two-wheeled vehicles, open waste burning, and flaring). To this end, a database on fuel consumption and emission factors specific to Africa was established using the most recent measurements. New spatial proxies (road network, power plant geographical coordinates) were used to convert national emissions into gridded inventories at a 0.1∘ × 0.1∘ spatial resolution. This inventory includes carbonaceous particles (black and organic carbon) and gaseous species (CO, NOx, SO2 and NMVOCs) for the period 1990–2015 with a yearly temporal resolution. We show that all pollutant emissions are globally increasing in Africa during the period 1990–2015 with a growth rate of 95 %, 86 %, 113 %, 112 %, 97 % and 130 % for BC, OC, NOx, CO, SO2 and NMVOCs, respectively. We also show that Western Africa is the highest emitting region of BC, OC, CO and NMVOCs, followed by Eastern Africa, largely due to domestic fire and traffic activities, while Southern Africa and Northern Africa are the highest emitting regions of SO2 and NOx due to industrial and power plant sources. Emissions from this inventory are compared to other regional and global inventories, and the emissions uncertainties are quantified by a Monte Carlo simulation. Finally, this inventory highlights key pollutant emission sectors in which mitigation scenarios should focus on. The DACCIWA inventory (https://doi.org/10.25326/56, Keita et al., 2020) including the annual gridded emission inventory for Africa for the period 1990–2015 is distributed by the Emissions of atmospheric Compounds and Compilation of Ancillary Data (ECCAD) system (https://eccad.aeris-data.fr/, last access: 19 July 2021​​​​​​​). For review purposes, ECCAD has set up an anonymous repository where subsets of the DACCIWA data can be accessed directly through https://www7.obs-mip.fr/eccad/essd-surf-emis-dacciwa/ (last access: 19 July 2021).

We use the global Community Earth System Model to investigate the response of secondary pollutants (ozone O3, secondary organic aerosols SOA) in response to modified emissions of primary pollutants during the COVID-19 pandemic. We use an estimate of the reduction in surface and aircraft emissions to derive the changes in the chemical composition of the atmosphere. We quantify the respective effects of the reductions in NOx and in VOC emissions, which, in most cases, affect oxidants in opposite ways. Using model simulations, we show that, relative to a situation in which the emission reductions are ignored, the ozone concentration increased only in a few NOx-saturated regions during the winter months of the pandemic when the titration of this molecule by NOx was reduced. In other regions, where ozone is NOx-controlled, the concentration of ozone decreased. SOA concentrations decrease in response to the concurrent reduction in the NOx and VOC emissions. Zonally averaged ozone concentrations in the free troposphere during Northern Hemisphere spring and summer were 5 to 15% lower than 19-year climatological values, in good quantitative agreement with ozone observations. We examine the response in free tropospheric ozone at different latitudes and specifically in the southern hemisphere, the tropics, the northern hemisphere mid-latitudes and polar region. About one third of this anomaly is attributed to the drastic reduction in air traffic during the pandemic, another third to reductions in surface emissions, the remainder to 2020 meteorological conditions, including the exceptional springtime Arctic stratospheric ozone depletion. We compare calculated changes in the vertical ozone profiles with values derived from ozone sonde observations.

AQ-WATCH (Air Quality: Worldwide Analysis and Forecasting of Atmospheric Composition for Health) is an international consortium, which co-develops and co-produces tailored products and services derived from space and in situ observational data for improving air quality forecasts and attribution. For this purpose, AQ-WATCH develops a supply chain leading to innovative downstream products and services for providing air quality information. These prototypes are based on existing space and in situ observations of air quality and tailored to the identified needs of international users. The project allows small and medium enterprises to integrate datasets associated with earth’s observations with advanced predictive models. These innovative products and services are aimed at improving public health and optimizing service provided by the energy sector in different regions of the world. The project also creates opportunities for new environmental technologies and enhances the interaction between research institutions, stakeholders and enterprises in support of the world-wide effort to improve air quality.The AQ-WATCH products and services are organized into 5 modules allowing users to access historical and air pollution data as well as air quality forecasts at a global and regional scale, to compare different air pollution reduction scenarios, to assess the effect of wildfires or fracking activities on air quality, and to derive the changes in solar irradiance due to the presence of dust in the atmosphere. These 5 modules include: (1) Global and regional air quality atlas, (2) Air quality attribution & mitigation, (3) Dust and fire forecasting system, (4) Fracking analysis, and (5) Air quality forecast. In this presentation, apart from an overview of the AQ-WATCH project and its products, extra focus will be put on the last product module, Air quality forecast, in particular on the effort of the consortium to provide air quality forecasts from their hosting regional models and the execution of the AQ-WATCH multi-model air quality forecast system.

The AQ-WATCH (Air Quality: Worldwide Analysis and Forecasting of Atmospheric Composition for Health) project, supported by the European Commission, is developing seven innovative products and services for improving air quality forecasts and attributing chemical sources. These prototypes are based on existing space and in-situ observations of air quality. They are tailored to the identified needs of international users and are aimed at improving public health. The prototypes include (1) a global and regional air quality atlas, (2) a forecast system for metropolitan areas, (3) a wildfire and visibility service, (4) a dust and solar energy service, (5) a pollution from fracking service, (6) an emission mitigation service and (7) an attribution service. The prototypes are being tested by prime users and integrated in a user-friendly toolkit. These products and services will be brought to the market.

We report on an evaluation of tropospheric ozone and its precursor gases in three atmospheric chemistry versions as implemented in the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS), referred to as IFS(CB05BASCOE), IFS(MOZART) and IFS(MOCAGE). While the model versions were forced with the same overall meteorology, emissions, transport and deposition schemes, they vary largely in their parameterisations describing atmospheric chemistry, including the organics degradation, heterogeneous chemistry and photolysis, as well as chemical solver. The model results from the three chemistry versions are compared against a range of aircraft field campaigns, surface observations, ozone-sondes and satellite observations, which provides quantification of the overall model uncertainty driven by the chemistry parameterisations. We find that they produce similar patterns and magnitudes for carbon monoxide (CO) and ozone (O3), as well as a range of non-methane hydrocarbons (NMHCs), with averaged differences for O3 (CO) within 10 % (20 %) throughout the troposphere. Most of the divergence in the magnitude of CO and NMHCs can be explained by differences in OH concentrations, which can reach up to 50 %, particularly at high latitudes. There are also comparatively large discrepancies between model versions for NO2, SO2 and HNO3, which are strongly influenced by secondary chemical production and loss. Other common biases in CO and NMHCs are mainly attributed to uncertainties in their emissions. This configuration of having various chemistry versions within IFS provides a quantification of uncertainties induced by chemistry modelling in the main CAMS global trace gas products beyond those that are constrained by data assimilation.

During the COVID-19 pandemic, the first lockdown period (March-May 2020) has led to an unprecedented reduction in pollutant emissions. For 3⁄4 of the more than 1,100 available monitoring stations in Europe, the average NO2 concentrations decreased by at least 25% (2.7 μg.m-3) compared to the average concentrations recorded during the same period of the previous seven years. The relative reduction was of similar magnitude in both urban and rural areas.We further investigate the spatial distribution of the O3 change. Relative to the seven years average, positive anomalies were observed in northern Europe and negative anomalies in southwestern Europe. However, the level of total oxidant (Ox = O3 + NO2) remained unchanged except in southwestern Europe where it decreased.At the global scale, the ozone concentration increased only in a few NOx-saturated regions. After presenting data from monitoring stations in Europe, we analyze the drivers of the change in surface ozone concentrations using the global Community Earth System Model. We contrast global simulations of the atmospheric composition with and without lockdown adjusted anthropogenic emissions for the COVID-19 period.By comparing the situation in Europe with that of the United States and China, we show that the reduced cloudiness in northern Europe played a significant role by shifting the photochemical partitioning between NO2 and O3 toward more ozone, while in the North China Plain, enhanced ozone concentrations resulted primarily from reduced emissions of primary pollutants.These results illustrate the complexity of the processes affecting ozone in the troposphere and hence the difficulty of implementing efficient regulations targeting air quality impacts.

We use the global Community Earth System Model to investigate the response of secondary pollutants (ozone O3, secondary organic aerosols SOA) in different parts of the world in response to modified emissions of primary pollutants during the COVID‐19 pandemic. We quantify the respective effects of the reductions in anthropogenic emissions and meteorological anomalies, including a discussion on long-term changes from the chemical climatology. We show that the level of NOx has been reduced by typically 40 % in China during February 2020 and by similar amounts in many areas of Europe and North America in mid-March to mid-April 2020. Relative to a situation in which the emission reductions are ignored and despite the calculated increase in hydroxyl and peroxy radicals, the ozone concentration increased only in a few NOx‐saturated regions during the winter months of the pandemic when the titration of this molecule by NOx was reduced. In other regions, where ozone is NOx‐controlled, the concentration of ozone decreased. Zonally averaged ozone concentrations in the free troposphere during Northern Hemisphere spring and summer were 5 to 15 % lower than 19-year climatological values, in good quantitative agreement with observations from ozonesondes and ground-based remote sensing from the Network for the Detection of Atmospheric Composition Change (NDACC). About one third of this anomaly is attributed to the drastic reduction in air traffic during the pandemic, another third to reductions in surface emissions, the remainder to 2020 meteorological conditions, including the exceptional springtime Arctic stratospheric ozone depletion. The overall COVID-19 reduction in mean northern hemisphere tropospheric ozone in June is less than 5 ppb below 400 hPa, but reaches 8 ppb at 250 hPa.

The worldwide spread of Covid-19 pandemic caused a dramatic cutback of human activities and triggered a large-scale atmospheric composition experiment. This unfortunate situation provides the opportunity to investigate the response of atmospheric composition to the shutdown measures. Our focus will be on China, where the pandemic emerged in January 2020, and thence strict lockdowns were enforced. Substantial, large-scale decreases in pollutants levels over China and subsequent recovery were revealed by spaceborne observations from TROPOMI instrument on board Sentinel-5 Precursor, as well as by in situ measurements. Most published work on this topic relied on observed changes in column abundances of nitrogen dioxide (NO2), a predominantly anthropogenic compound and an important precursor for ozone production and secondary aerosol formation. Our work adds to this picture by studing the evolution of two other satellite-derived compounds, formaldehyde (HCHO) and peroxyacylnitrate (PAN), observed by TROPOMI and IASI, respectively. HCHO is an intermediate product in the chemical processing of volatile organic compounds (VOCs) of anthropogenic and natural origin. PAN is formed in the oxidation of anthropogenic and biogenic VOCs, and constitute the principal tropospheric NOx reservoir, enabling the transport and release of NOx away from the sources. Chemistry-transport simulations of PAN are challenging due to large uncertainties in formation mechanisms and precursor emissions. We will evaluate and analyze the observed variability of NO2, HCHO, and PAN columns using model simulations with the MAGRITTE v1.1 regional CTM run at 0.5ox0.5o resolution over China for 2019 and 2020. The model uses updated anthropogenic emissions from the CONFORM dataset, which takes into account the reductions during the shutdowns based on traffic and other economic activity data.

In order to fight the spread of the global COVID-19 pandemic, most of the world countries have taken control measures such as lockdowns during a few weeks to a few months. These lockdowns had significant impacts on economic and personal activities in many countries. Several studies using satellite and surface observations have reported important changes in the spatial and temporal distributions of atmospheric pollutants and greenhouse gases. Global and regional chemistry-transport model studies are being performed in order to analyze the impact of these lockdowns on the distribution of atmospheric compounds. These modeling studies aim at evaluating the impact of the regional lockdowns at the global scale. In order to provide input for the global and regional model simulations, a dataset providing adjustment factors (AFs) that can easily be applied to global and regional emission inventories has been developed. This dataset provides, for the January–August 2020 period, gridded AFs at a 0.1 × 0.1 latitude/longitude degree resolution, on a daily or monthly basis for the transportation (road, air and ship traffic), power generation, industry and residential sectors. The quantification of AFs is based on activity data collected from different databases and previously published studies. A range of AFs is provided at each grid point for model sensitivity studies. The emission AFs developed in this study are applied to the CAMS global inventory (CAMS-GLOB-ANT_v4.2_R1.1), and the changes in emissions of the main pollutants are discussed for different regions of the world and the first six months of 2020. Maximum decreases in the emissions are found in February in Eastern China, with an average reduction of 20–30 % in NOx, NMVOCs and SO2 relative to the reference emissions. In the other regions, the maximum changes occur in April, with average reductions of 20–30 % for NOx, NMVOCs and CO in Europe and North America and larger decreases (30–50 %) in South America. In India and African regions, NOx and NMVOCs emissions are reduced by 15–30 %. For the others species, the maximum reductions are generally less than 15 %, except in South America, where large decreases in CO and BC are estimated. As discussed in the paper, reductions vary highly across regions and sectors, due to the differences in the duration of the lockdowns before partial or complete recovery. The dataset providing a range of AFs (average and average ± standard deviation) is called CONFORM (COvid adjustmeNt Factor fOR eMissions) (https://doi.org/10.25326/88). It is distributed by the Emissions of atmospheric Compounds and Compilation of Ancillary Data (ECCAD) database (https://eccad.aeris-data.fr/).

Using the CAM-chem Model, we simulate the response of chemical species in the free troposphere to scenarios of primary pollutant emission reductions during the COVID-19 pandemic. Zonally averaged ozone in the free troposphere during Northern Hemisphere spring and summer is found to be 5%–15% lower than 19-yr climatological values, in good agreement with observations. About one third of this anomaly is attributed to the reduction scenario of air traffic during the pandemic, another third to the reduction scenario of surface emissions, the remainder to 2020 meteorological conditions, including the exceptional springtime Arctic stratospheric ozone depletion. For the combined emission reductions, the overall COVID-19 reduction in northern hemisphere tropospheric ozone in June is less than 5ppb below 400hPa, but reaches 8ppb at 250hPa. In the Southern Hemisphere, COVID-19 related ozone reductions by 4%–6% were masked by comparable ozone increases due to other changes in 2020.

We use the global Community Earth System Model to investigate the response of secondary pollutants (ozone O3, secondary organic aerosols SOA) in different parts of the world in response to modified emissions of primary pollutants during the COVID‐19 pandemic. We quantify the respective effects of the reductions in NOx and in volatile organic carbon (VOC) emissions, which, in most cases, affect oxidants in opposite ways. Using model simulations, we show that the level of NOx has been reduced by typically 40% in China during February 2020 and by similar amounts in many areas of Europe and North America in mid‐March to mid‐April 2020, in good agreement with space and surface observations. We show that, relative to a situation in which the emission reductions are ignored and despite the calculated increase in hydroxyl and peroxy radicals, the ozone concentration increased only in a few NOx‐saturated regions (northern China, northern Europe, and the US) during the winter months of the pandemic when the titration of this molecule by NOx was reduced. In other regions, where ozone is NOx‐controlled, the concentration of ozone decreased. SOA concentrations decrease in response to the concurrent reduction in the NOx and VOC emissions. The model also shows that atmospheric meteorological anomalies produced substantial variations in the concentrations of chemical species during the pandemic. In Europe, for example, a large fraction of the ozone increase in February 2020 was associated with meteorological anomalies, while in the North China Plain, enhanced ozone concentrations resulted primarily from reduced emissions of primary pollutants., Plain Language Summary: With the reduction in economic activities following the COVID‐19 pandemic outbreak in early 2020, most emissions of air pollutants (i.e., nitrogen oxides [NOx], carbon monoxide [CO], sulfur dioxide [SO2], volatile organic carbon [VOC], black carbon [BC], organic carbon [OC]) have decreased substantially during several months in different regions of the world. This unintended global experiment offered a glimpse into a potential future in which air quality would be improved. Here, a global atmospheric model is used to assess the changes in the chemical composition of the atmosphere during the pandemic period and in the related chemical processes that lead to the formation of ozone (O3) and secondary organic aerosols (SOA). The study illustrates the nonlinearity of the air quality response to reduced NOx and VOC emissions, which depends on the chemical environment including the background level of nitrogen oxides. Meteorological variability can lead to anomalies in the concentration of chemical species with magnitudes that are as large or even larger than the perturbations due to COVID‐induced changes in the emissions., Key Points: During the COVID‐19 lockdown, the atmospheric concentration of primary pollutants (NOx, VOCs, CO, SO2) was considerably reduced The concentration of secondary pollutants increased in NOx‐saturated areas and decreased in NOx‐limited areas The response of the chemical system depends on the relative changes in NOx and VOC emissions, and is affected by weather variability, AQ‐WATCH European project, HORIZON 2020 Research and Innovation Action, Hong Kong Research Grants Council

In the framework of the INDAAF (International Network to study Deposition and Atmospheric chemistry in AFrica) program, atmospheric aerosols were collected in PM2.5 and PM10 size fractions at Djougou, Benin, in the West Africa, from November, 2005 to October, 2009. Particulate carbon, ionic species, and trace metals were analyzed. Weekly PM2.5 and PM10 total mass concentrations varied between 0.7 and 47.3 µg m−3 and 1.4–148.3 µg m−3, respectively. We grouped the aerosol chemical compounds into four classes: dust, particulate organic matter (POM), elemental carbon (EC), and ions. We studied the annual variation of each class to determine their contribution in the total aerosol mass concentration and finally to investigate their potential emission sources. On an annual basis, the species presented a well-marked seasonality, with the peak of mass concentration for both sizes registered in dry season, 67 ± 2 to 86 ± 9 versus 14 ± 9 to 34 ± 5% in wet season. These values emphasized the seasonality of the emissions and the relative weak interannual standard deviation indicates the low variability of the seasonality. At the seasonal scale, major contributions to the aerosol chemistry in the dry season are: dust (26–59%), POM (30–59%), EC (5–9%), and ions (3–5%), suggesting a predominance of Sahelian and Saharan dust emissions and biomass burning source in this season. In the wet season, POM is predominant, followed by dust, EC, and ions. These results point out the contribution of surrounded biofuel combustion used for cooking and biogenic emissions during the wet season.

Air pollution in West Africa is far to be well characterized. It was the rationale of the Air Pollution and Health work package in the DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) program. Intensive measurement campaigns were running in two West African capitals (Abidjan in Côte d’Ivoire and Cotonou in Benin), to examine size distribution of the particulate matter (PM) concentrations and their chemical composition (Elemental Carbon (EC), Organic Carbon (OC), Water-soluble organic carbon (WSOC), Water-soluble inorganic ions (WSI) and trace metals). This work aims to characterize PM from different sites in Abidjan, the economic capital of Cote d’Ivoire, typical of Domestic Fire (ADF), Traffic (AT) and Waste Burning (AWB) and Cotonou, the capital of Benin, representative of Traffic (CT). These selected sites, impacted by a large amount of pollution levels, are representative of the main combustion sources prevailing in South West Africa during dry and wet seasons. To address this concern, intensive campaigns in Abidjan and Cotonou have been conducted in July (2015 and 2016) and January (2016 and 2017). Results show a well-marked seasonality, inter-annual and spatial variabilities and the PM levels at the studied areas are generally higher than the WHO guidelines. The average mass concentrations in the wet season were 90.3, 104.1, 69.1 and 517.3 μg m−3 at AT, CT, AWB and ADF sites, respectively. The largest value at ADF site is due to the contribution of smoking and roasting activities. By contrast in the dry season, the concentrations increase to 141.3, 269.7 and 175.3 μg m−3 at AT, CT and AWB site, respectively whereas at ADF site concentration decreases to 375.7 μg m−3. The chemical aerosol mass closure shows that dust contributed for 25–65 % at the both traffic and AWB sites, and 10–30 % at ADF with a clear seasonal cycle. A large variability of POM is observed with contribution range of 37–68 % at ADF, 20–42 % at AT, 10–34 % at AWB and 15–22 % at CT. The contribution of WSI to bulk PM (lower than 20 %) is 2–3 times larger in wet season than dry season, except at ADF site where no season variation is observed. The most dominant species in WSI fraction at ADF are chloride (18–36 % of the total ions), potassium (8–22 %) and calcium (13–25 %), while at the rest of the sites, nitrates (21–36 %), chlorides (6–30 %) and sulfates (9–20 %) are higher. At all sites, the proportion of EC is twice higher in dry season than in wet season. Carbonaceous aerosol (sum of EC and POM) and dust particles are the two major contributors to the different particle fractions with carbonaceous aerosol predominant at Abidjan and dust at Cotonou. The highest carbonaceous aerosol contribution is obtained at ADF (up to 75 % of total PM), while at the other sites its contribution ranges between 18 and 35 %. WSOC levels are higher at the traffic sites during the dry season, while during the wet season they are maximum at ADF and AWB sites. Element trace characterization is also determined, showing predominance of Al, Na and Ca followed by Fe, K and Mg. Our study highlights the contribution of different traffic emissions in two major West African cities in atmospheric aerosol composition but also the one of domestic fire and waste combustion sources. It constitutes an original database to characterize urban air pollution for specific African combustion sources.

International audience; Flaring emissions are a major concern due to large uncertainties in the amount of chemical compounds released into the atmosphere and their evolution with time. A methodology based on DMSP (Defense Meteorological Satellite Program) nighttime light data combined with regional gas flaring volumes from National Oceanic and Atmospheric Administration's National Centers for Environmental Information (NOAA-NCEI) has been developed to estimate flaring emissions. This method is validated in Nigeria where individual field company data are available. The spatial distribution of CO2, CH4, NMVOCs, CO, OC, BC, SO2 and NOx is derived for the African continent for the period 1995–2010. A range of the emissions due to flaring is estimated based on the range of emission factors (EFs) for each chemical species. An average decrease in CO2 emissions of about 30% is found over Africa from 1995 to 2010, with Nigeria being the largest contributor to this reduction (up to 50%). Changes in the spatial distribution with time indicate local increases, particularly at offshore platforms, which are attributed to a lack of regulations as well as aging infrastructures in oil and gas fields. Comparisons with current inventories reveal differences in the location and magnitude of point source emissions. For chemical compounds such as NMVOCs and CH4, the ECLIPSE and EDGAR country-level values are considerably higher than the highest flaring emission estimated in this study for 2005. For species such as CO, OC, BC, SO2 and NOx, the emissions provided by the ECLIPSE and EDGAR inventories are generally within the same order of magnitude as the average values found in this study, with the exception of OC, BC and SO2 in which EDGAR provides much lower emissions. These discrepancies are likely due to either differences in the methodologies used to estimate the emissions, in the values of the emission factors considered, or in the definition of flaring sector. Our current estimations suggest that BC, CH4 and CO2 flaring emissions in Africa account for 1–15% (on average 7%), 0.5–8% (on average 2%) and 8–13% (on average 11%) of African total anthropogenic emissions, respectively. The contribution of flaring to African anthropogenic emissions varies widely among countries. For example, in Nigeria the average emissions due to flaring are estimated to be as high as 18% for BC, 10% for CH4 and 50% for CO2, which is significantly greater than the continental average and highlights the importance of emissions in flaring areas.

We report on an evaluation of tropospheric ozone and its precursor gases in three atmospheric chemistry versions as implemented in ECMWF’s Integrated Forecasting System (IFS), referred to as IFS(CB05BASCOE), IFS(MOZART) and IFS(MOCAGE). While the model versions were forced with the same overall meteorology, emissions, transport and deposition schemes, they vary largely in their parameterizations describing atmospheric chemistry, including the organics degradation, heterogeneous chemistry and photolysis, as well as chemical solver. The model results from the three chemistry versions are compared against a range of aircraft field campaigns, ozone sondes and satellite observations, which provides quantification of the overall model uncertainty driven by the chemistry parameterizations. We find that they produce similar patterns and magnitudes for carbon monoxide (CO) and ozone (O3), as well as a range of non-methane hydrocarbons (NMHCs), with averaged differences for O3 (CO) within 10 % (20 %) throughout the troposphere. Most of the divergence in the magnitude of NMHCs can be explained by differences in OH concentrations, which can reach up to 50 % particularly at high latitudes. Also comparatively large discrepancies between model versions exist for NO2, SO2 and HNO3, which are strongly influenced by secondary chemical production and loss. Other, common biases in CO and NMHCs are mainly attributed to uncertainties in their emissions. This configuration of having various chemistry versions within IFS provides a quantification of uncertainties induced by chemistry modeling in the main CAMS global trace gas products beyond those that are constrained by data-assimilation.

Accurate information on surface emissions is critical for understanding the current chemical composition of the atmosphere and for forecast simulations. Many research teams worked during the past years to better quantify emissions in different parts of the world, and to develop inventories of anthropogenic emissions for different periods. An evaluation of the most recent datasets providing emissions for Asia for the 1960–2014 period is discussed in this chapter for different gaseous and particulate compounds, i.e. carbon monoxide, nitrogen oxides, non-methane volatile organic compounds, sulfur dioxide, ammonia, black carbon, organic carbon, and particulate matter PM10 and PM2.5. The comparison between the inventories is used to quantify the range of the emissions for several regions and different periods. Since very little information is available concerning the uncertainties on emissions in the different regions of the world, we use the comparison between the different datasets to provide some information on these uncertainties.

Real time measurements of Black Carbon (BC) in PM 2.5 aerosols were performed during AMMA and POLCA programs, between 2005 and 2010 in Cotonou (Benin), Dakar (Senegal), Bamako (Mali), and Yaounde (Cameroon). Indeed, BC was chosen as a metric because of its interest as an urban pollutant. The instrumented sites are representative of the traffic source. At Dakar, BC concentrations are high from November to April (13,000 ± 3500 ng m −3 ) and lower from May to September (8000 ± 3200 ng m −3 ). In dry season (November–April), high BC concentrations occurred as a result of northeasterly long-range transport of polluted air masses over West Africa, in addition to local emissions. However, during wet season (May–September) reduced traffic levels, school vacations and wet deposition processes contribute to lower BC concentration levels. Measured diurnal BC peak concentrations, at all sites, mainly occur during morning and evening rush-hour periods, indicating the paramount role of traffic. Highest values are observed between 5–9 a.m. and from 5 p.m. to 9 p.m. depending on the site, while lowest are occurred at night time and middle afternoon when activities of the population are reduced. BC source apportionment from absorption measurements also confirmed the relative importance of traffic (88%) versus biomass burning (12%). Also, BC measurements were functions of days of the week, with highest values occurring on Fridays and lowest ones on Sundays. Spatial variations associated to BC levels are very different from one site to another, revealing different types of sources with strong variations at the regional scale. It appears that mean BC concentrations in Dakar are lower by a factor of two, compared to those observed in Bamako, but remain higher than in some other West African sites (e.g. Cotonou, Yaounde). Overall, BC concentrations in our different sites are comparable to reported European and Asian megacity levels. Finally, using measured BC/PM 2.5 ratios, we have estimated PM 2.5 mass concentrations in Dakar from June 2008 to June 2009 to be 44.4 ± 14.3 μg m −3 , well above the WHO (2005) threshold of 10 μg m −3 . This paper clearly highlights high pollution levels in West African large cities, with potential important impacts on the health of the regional population.

International audience; Air pollution is a major issue for global environment as well as human health and well-being. Recently, satellites which are equipped with relevant air quality instruments have been placed into orbit. In this paper, we first present a review on satellite remote sensing of particulate pollution. We then present new results for Europe and on African cities particulate air pollutants using POLDER satellite data. Based on satellite AOD observations, we show that the number of days exceeding the 15.4 μg/m3 threshold is twice frequent in Ouagadougou, Burkina-Faso than in Paris, France. At the regional scale, we observe that the northern coast of the golf of Guinea is dramatically impacted by poor air quality.

International audience; BACKGROUND: The involvement of particulate matter (PM) in cardiorespiratory diseases is now established in developed countries whereas in developing areas such as Africa with a high level of specific pollution, PM pollution and its effects are poorly studied. Our objective was to characterize the biological reactivity of urban African aerosols on human bronchial epithelial cells in relation to PM physico-chemical properties to identify toxic sources. METHODS: Size-speciated aerosol chemical composition was analyzed in Bamako (BK, Mali, 2 samples with one having desert dust event BK1) and Dakar (DK; Senegal) for Ultrafine UF, Fine F and Coarse C PM. PM reactivity was studied in human bronchial epithelial cells investigating six biomarkers (oxidative stress responsive genes and pro-inflammatory cytokines). RESULTS: PM mass concentrations were mainly distributed in coarse mode (60%) and were impressive in BK1 due to the desert dust event. BK2 and DK samples showed a high content of total carbon characteristic of urban areas. The DK sample had huge PAH quantities in bulk aerosol compared with BK that had more water soluble organic carbon and metals. Whatever the site, UF and F PM triggered the mRNA expression of the different biomarkers whereas coarse PM had little or no effect. The GM-CSF biomarker was the most discriminating and showed the strongest pro-inflammatory effect of BK2 PM. The analysis of gene expression signature and of their correlation with main PM compounds revealed that PM-induced responses are mainly related to organic compounds. The toxicity of African aerosols is carried by the finest PM as with Parisian aerosols, but when considering PM mass concentrations, the African population is more highly exposed to toxic particulate pollution than French population. Regarding the prevailing sources in each site, aerosol biological impacts are higher for incomplete combustion sources resulting from two-wheel vehicles and domestic fires than from diesel vehicles (Dakar). Desert dust events seem to produce fewer biological impacts than anthropogenic sources. DISCUSSION: Our study shows that combustion sources contribute to the high toxicity of F and UF PM of African urban aerosols, and underlines the importance of emission mitigation and the imperative need to evaluate and to regulate particulate pollution in Africa.