This work is part of the DACCIWA FP7 project (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) in the framework of the Work Package 2 Air Pollution and Health. This study aims to ...characterize urban air pollution levels through the measurement of NO2, SO2, NH3, HNO3 and O3 in Abidjan, the economic capital of Côte d'Ivoire. Measurements of inorganic gaseous pollutants, i.e. NO2, SO2, NH3, HNO3 and O3 were performed in Abidjan during an intensive campaign within the dry season (15 December 2015 to 16 February 2016), using INDAAF (International Network to study Deposition and Atmospheric chemistry in AFrica) passive samplers exposed in duplicate for 2-week periods. Twenty-one sites were selected in the district of Abidjan to be representative of various anthropogenic and natural sources of air pollution in the city. Results from this intensive campaign show that gas concentrations are strongly linked to surrounding pollution sources and show a high spatial variability. Also, NH3, NO2 and O3 gases were present at relatively higher concentrations at all the sites. NH3 average concentrations varied between 9.1 ± 1.7 ppb at a suburban site and 102.1 ± 9.1 ppb at a domestic fires site. NO2 mean concentration varied from 2.7 ± 0.1 ppb at a suburban site to 25.0 ± 1.7 ppb at an industrial site. Moreover, we measured the highest O3 concentration at the two coastal sites of Gonzagueville and Félix-Houphouët-Boigny International Airport located in the southeast of the city, with average concentrations of 19.1 ± 1.7 and 18.8 ± 3.0 ppb, respectively. The SO2 average concentration never exceeded 7.2 ± 1.2 ppb over all the sites, with 71.5 % of the sampling sites showing concentrations ranging between 0.4 and 1.9 ppb. The HNO3 average concentration ranged between 0.2 and 1.4 ppb. All these results were combined with meteorological parameters to provide the first mapping of gaseous pollutants on the scale of the district of Abidjan using geostatistical analysis (ArcGIS software). Spatial distribution results emphasize the importance of the domestic fires source and the significant impact of the traffic emissions on the scale of the city. In addition, in this work we propose a first overview of gaseous SO2 and NO2 concentrations on the scale of several African cities by comparing literature to our values. The daily SO2 standard of World Health Organization (WHO) is exceeded in most of the cities reported in the overview, with concentrations ranging from 0.2 to 3662 µg m−3. Annual NO2 concentrations ranged from 2 to 175 µg m−3, which are lower than the WHO threshold. As a conclusion, this study constitutes an original database to characterize urban air pollution and a first attempt towards presenting a spatial distribution of the pollution levels at the scale of the metropolis of Abidjan. This work should draw the attention of the African public authorities to the necessity of building an air quality monitoring network in order to (1) to define national standards and to better control the pollutants emissions and (2) to investigate the impact on the health of the growing population in developing African countries.
A number of campaigns have been
carried out to establish the emission factors of pollutants from fuel
combustion in West Africa, as part of work package 2 (“Air Pollution and
Health”) of the DACCIWA ...(Dynamics-Aerosol-Chemistry-Cloud Interactions in
West Africa) FP7 program. Emission sources considered here include wood
(hevea and iroko) and charcoal burning, charcoal making, open trash burning,
and vehicle emissions, including trucks, cars, buses and two-wheeled
vehicles. Emission factors of total particulate matter (TPM), elemental
carbon (EC), primary organic carbon (OC) and volatile organic compounds
(VOCs) have been established. In addition, emission factor measurements were
performed in combustion chambers in order to reproduce field burning
conditions for a tropical hardwood (hevea), and obtain particulate emission
factors by size (PM0.25, PM1, PM2.5 and PM10). Particle
samples were collected on quartz fiber filters and analyzed using gravimetric
method for TPM and thermal methods for EC and OC. The emission factors of 58
VOC species were determined using offline sampling on a sorbent tube.
Emission factor results for two species of tropical hardwood burning of EC,
OC and TPM are 0.98 ± 0.46 g kg−1 of fuel burned (g kg−1),
11.05 ± 4.55 and 41.12 ± 24.62 g kg−1, respectively. For
traffic sources, the highest emission factors among particulate species are
found for the two-wheeled vehicles with two-stroke engines
(2.74 g kg−1 fuel for EC, 65.11 g kg−1 fuel for OC and
496 g kg−1 fuel for TPM). The largest VOC emissions are observed for
two-stroke two-wheeled vehicles, which are up to 3 times higher than
emissions from light-duty and heavy-duty vehicles. Isoprene and monoterpenes,
which are usually associated with biogenic emissions, are present in almost
all anthropogenic sources investigated during this work and could be as
significant as aromatic emissions in wood burning (1 g kg−1 fuel). EC
is primarily emitted in the ultrafine fraction, with 77 % of the total mass
being emitted as particles smaller than 0.25 µm. The particles and
VOC emission factors obtained in this study are generally higher than those
in the literature whose values are discussed in this paper. This study
underlines the important role of in situ measurements in deriving realistic
and representative emission factors.
Naturally and anthropogenically emitted aerosols, which are determined by their physical and chemical properties, have an impact on both air quality and the radiative properties of the earth. An ...important source of atmospheric particulate matter (PM) in South Africa is household combustion for space heating and cooking, which predominantly occurs in low-income urban settlements. The aim of this study was to conduct a detailed size-resolved assessment of chemical characteristics of aerosols associated with household combustion through the collection of particulates in low-income urban settlements in South Africa to quantify the extent of the impacts of atmospheric pollution. Outdoor (ambient) and indoor aerosols in different size fractions were collected during summer and winter in four low-income urban settlements located in the north-eastern interior on the South African Highveld, i.e. Kwadela, Kwazamokuhle, Zamdela, and Jouberton. Mass concentration and chemical composition was determined for three size fractions, namely, PM.sub.1, PM.sub.2.5, and PM.sub.2.5-10 . The highest concentrations of particulates were measured indoors with the highest mass concentration determined in the indoor PM.sub.2.5-10 (coarse) size fraction. However, the highest mass concentrations were determined in PM.sub.1 in all outdoor aerosol samples collected during winter and summer, and in indoor samples collected during summer.
To date, most models dedicated to the investigation of aerosol direct or semi‐direct radiative forcings have assumed the various aerosol components to be either completely externally mixed or ...homogeneously internally mixed. Some recent works have shown that a core‐shell treatment of particles should be more realistic, leading to significant differences in the radiative impact as compared to only externally or well‐internally mixed states. To account for these studies, an optical module, ORISAM‐RAD, has been developed for computing aerosol radiative properties under the hypothesis of internally mixed particles with a n‐layer spherical concentric structure. Mesoscale simulations using ORISAM‐RAD, coupled with the 3D mesoscale model Meso‐NH‐C, have been performed for one selected day (06/24/2001) during the ESCOMPTE experiment in the Marseilles‐Fos/Berre region, which illustrate the ability of this new module to reproduce spatial heterogeneities of measured single scattering albedo (ωo), due to industrial and/or urban pollution plumes.
Urbanization is an issue that is strongly emerging in southern West Africa (sWA). There is a lack of full understanding on chemical compositions and personal exposure levels to fine particulate ...matter (hereafter defined as PE PM2.5) and its health risks related to various anthropogenic sources in this region. In this study, PE PM2.5 was studied in dry (January) and wet (July) seasons of 2016 for the first time to characterize the contributions of a domestic fire site (DF) to the exposure of women and a waste burning site (WB) to that of students in Abidjan, Côte d'Ivoire, and a motorcycle traffic site (MT) to that of drivers in Cotonou, Benin. The average PE PM2.5 mass concentrations were 331.7±190.7, 356.9±71.9 and 242.8±67.6 µg m−3 at DF, WB and MT sites for women, students and drivers, which were 2.4, 10.3 and 6.4 times the ambient PM2.5 concentrations, respectively. Elevated PE PM2.5 levels in the dry season were found at DF (358.8±100.5 µg m−3), WB (494.3±15.8 µg m−3) and MT (335.1±72.1 µg m−3) sites, on average 15 % higher than that at DF and 55 % higher at both WB and MT sites in the wet season. The seasonal variations were attributed to emission sources, meteorological factors and personal activities. In addition, the results show that geological material (35.8 %, 46.0 % and 42.4 %) and organic matter (34.1 %, 23.3 % and 24.9 %) were the major components of PE PM2.5 at DF, WB and MT sites. It is worth noting that the contribution of heavy metals was higher at WB (1.0 %) than at DF (0.7 %) and MT (0.4 %) sites, strongly influenced by waste burning emission. This results in the highest non-cancer risks of heavy metals to students, 5.1 and 4.8 times the values for women and drivers, respectively. By conducting organic speciation, fingerprints were used to access the exposure and identify the source contributions from typical local anthropogenic sources. The women's exposure concentration to particulate polycyclic aromatic hydrocarbons (PAHs) at DF (77.4±47.9 ng m−3) was 1.6 and 2.1 times, respectively, that of students at WB (49.9±30.7 ng m−3) and of drivers at MT (37.0±7.4 ng m−3). This can be associated with the higher contributions from solid fuels' burning and meat grilling activities to women, resulting in a level 5 times in exceedance of the cancer risk safety threshold (1×10-6). Phthalate esters (PAEs), commonly used as plasticizers in products, were in high levels in the student exposure PM2.5 samples (1380.4±335.2 ng m−3), owing to obvious waste burning activities nearby. The drivers' exposures to fossil fuel combustion markers of hopanes in PE PM2.5 at MT (50.9±7.9 ng m−3) was 3.0–3.3 times those for women at DF (17.1±6.4 ng m−3) and students at WB (15.6±6.1 ng m−3). Overall, the current study shows that wood combustion, waste burning, fugitive dust and motor vehicle emissions were the dominant sources of PE PM2.5 and mainly contributed to its toxicities. The exposure to the heavy metals Pb and Mn caused high non-cancer risks to students at WB, while the severe cancer risk of PAHs was found for women at DF via inhalation. The result of this study provides original data, initial perspective of PM2.5 personal exposure and health risk assessment in the developing areas. The information encourages the governments to improve the air quality and living standards of residents in this region.
Several field campaigns were conducted in the framework of the
Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA)
project to measure a broad range of atmospheric constituents. ...Here we
present the analysis of an unprecedented and comprehensive dataset
integrating up to 56 volatile organic compounds (VOCs) from ambient
sites and emission sources. VOCs were collected on multi-sorbent tubes in the
coastal city of Abidjan, Côte d'Ivoire, in winter and summer 2016 and
later analysed by gas chromatography coupled with flame ionization and mass
spectrometer detectors (GC-FID and GC-MS) at the laboratory. The comparison between VOC emission source profiles and ambient profiles
suggests the substantial impact of two-stroke motorized two-wheel vehicles
and domestic fires on the composition of Abidjan's atmosphere. However,
despite high VOC concentrations near-source, moderate ambient levels were
observed (by factors of 10 to 4000 lower), similar to the concentrations
observed in northern mid-latitude urban areas. Besides photochemistry, the
reported high wind speeds seem to be an essential factor that regulates air
pollution levels in Abidjan. Emission ratios (ΔVOC∕ΔCO) were established based on
real-world measurements achieved for a selected number of representative
combustion sources. Maximum measured molar mass emissions were observed from
two-wheel vehicles, surpassing other regional sources by 2 orders of
magnitude. Local practices like waste burning also make a significant
contribution to VOC emissions, higher than those from light-duty vehicles by
1.5 to 8 orders of magnitude. These sources also largely govern the VOC's
atmospheric impacts in terms of OH reactivity, secondary organic aerosol
formation (SOAP), and photochemical ozone creation potential (POCP). While
the contribution of aromatics dominates the atmospheric impact, our
measurements reveal the systematic presence of anthropogenic terpenoids in
all residential combustion sectors. Finally, emission factors were used to
retrieve and quantify VOC emissions from the main anthropogenic source
sectors at the national level. Our detailed estimation of VOC emissions
suggests that the road transport sector is the dominant source in Côte
d'Ivoire, emitting around 1200 Gg yr−1 of gas-phase VOCs. These new
estimates are 100 and 160 times larger than global inventory estimations
from MACCity or EDGAR (v4.3.2), respectively. Additionally, the residential
sector is largely underestimated in the global emission inventories, by
factors of 13 to 43. Considering only Côte d'Ivoire, these new estimates
for VOCs are 3 to 6 times higher than the whole of Europe. Given the
significant underestimation of VOC emissions from the transport and residential
sectors in Côte d'Ivoire, there is an urgent need to build more
realistic and region-specific emission inventories for the entire West
African region. This might be true not only for VOCs, but also for all atmospheric
pollutants. The lack of waste burning, wood fuel burning and charcoal
burning, and fabrication representation in regional inventories also needs to
be addressed, particularly in low-income areas where these types of
activities are ubiquitous sources of VOC emissions.
Particulate emissions from biomass burning can both alter the atmosphere's radiative balance and cause significant harm to human health. However, due to the large effect on emissions caused by even ...small alterations to the way in which a fuel burns, it is difficult to study particulate production of biomass combustion mechanistically and in a repeatable manner. In order to address this gap, in this study, small wood samples sourced from Côte D'Ivoire in West Africa were burned in a highly controlled laboratory environment. The shape and mass of samples, available airflow and surrounding thermal environment were carefully regulated. Organic aerosol and refractory black carbon emissions were measured in real time using an Aerosol Mass Spectrometer and a Single Particle Soot Photometer, respectively. This methodology produced remarkably repeatable results, allowing aerosol emissions to be mapped directly onto different phases of combustion. Emissions from pyrolysis were visible as a distinct phase before flaming was established. After flaming combustion was initiated, a black-carbon-dominant flame was observed during which very little organic aerosol was produced, followed by a period that was dominated by organic-carbon-producing smouldering combustion, despite the presence of residual flaming. During pyrolysis and smouldering, the two phases producing organic aerosol, distinct mass spectral signatures that correspond to previously reported variations in biofuel emissions measured in the atmosphere are found. Organic aerosol emission factors averaged over an entire combustion event were found to be representative of the time spent in the pyrolysis and smouldering phases, rather than reflecting a coupling between emissions and the mass loss of the sample. Further exploration of aerosol yields from similarly carefully controlled fires and a careful comparison with data from macroscopic fires and real-world emissions will help to deliver greater constraints on the variability of particulate emissions in atmospheric systems.
Urban air pollution in West Africa has yet to be well characterized. In the frame of DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) program, intensive measurement campaigns ...were performed in Abidjan (Côte d'Ivoire) and Cotonou (Benin), in dry (January 2016 and 2017) and wet (July 2015 and 2016) seasons, at different sites chosen to be representative of African urban combustion sources, i.e., domestic fires (ADF), traffic (AT) and waste burning (AWB) sources in Abidjan and traffic source in Cotonou (CT). Both the size distribution of particulate matter (PM) and their chemical composition including elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC), water-soluble inorganic ions (WSI) and trace metals were examined. Results show very high PM concentrations at all sites and a well-marked seasonality as well as a strong spatial variation. The average PM2.5 mass concentrations during the wet season are 517.3, 104.1, 90.3, and 69.1 µg m−3 at the ADF, CT, AT, and AWB sites, respectively. In the dry season, PM2.5 concentrations decrease to 375.7 µg m−3 at the ADF site, while they increase to 269.7, 141.3, and 175.3 µg m−3 at the CT, AT, and AWB sites, respectively. The annual PM2.5 levels at almost all sites are significantly higher than the WHO guideline level of 10 µg m−3. As for PM mass, (EC) and (OC) concentrations are also maximal at the ADF site, accounting for up to 69 % of the total PM mass. Such a high content is mainly linked to wood burning for domestic cooking and commercial food smoking activities. Dust contributions are dominant at CT (57 %–80 %), AT (20 %–70 %), and AWB (30 %–69 %) sites and especially in the coarse and fine-particle modes at the CT site and in the coarse fraction at the AT site, which may be explained by the impact of long-range desert-dust transport and resuspended particles from the roads, in addition to anthropogenic sources. The contributions of WSI to the total PM mass, mainly driven by chloride, nitrate, and calcium in the fine and/or large particles, are highly variable according to the sites but remain less than 30 %. Values are generally 1–3 times higher in the wet season than in the dry season. This is due not only to anthropogenic emissions but also to nitrate formation by reaction processes and natural emissions. The concentrations of trace elements reflect well the trends in dust at the traffic and AWB sites, with a predominance of Al, Na, Ca, Fe, and K, keys markers of crustal dust. This study constitutes an original database that characterizes specific African combustion sources.
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