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.
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.
Particulate pollution in West African cities seriously impacts public human health. Assessing the levels of pollution to which populations are exposed is problematic, as to date very few countries in ...Africa have an air quality monitoring network in place. However, given the specific anthropogenic sources present in West African countries and the increase in their projected emissions in the coming years if no regulations are put in place, solutions must be found. This study evaluates with a simple existing methodology particulate air pollution in two West African cities (Korhogo and Abidjan in Cote d'Ivoire) which have different population practices and local meteorology. From two measurement campaigns at about ten sites during the dry season and using the inverse distance-weighted interpolation method, maps of spatial variation in PM_(10) and PM_(2.5) concentrations are obtained at the scale of each of these cities, which provide a snapshot of the concentration levels to which populations are actually exposed. The results of this study showed that populations in low- and middle-income areas are exposed to higher concentrations than those in high-income areas. The analysis of the relative contribution of fine particles to coarse particles shows that PM_(2.5) contributes to PM_(10) at less than 40% in Korhogo but more than 50% in Abidjan. Daily average concentrations of PM_(2.5) are all above WHO standards, and are 2 to 8 times higher in Korhogo, while in Abidjan they are up to 4 times higher. The daily profiles of the mean hourly concentrations of the sites are similar across all sites in Korhogo, while in Abidjan, that of some sites show some differences. This study, by the methodology used, offers an opportunity for different research teams to assess at lower cost the population's exposure levels to urban particulate pollution.
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.
Road traffic emission inventories based on bottom-up methodology, are calculated for each road segment from fuel consumption and traffic volume data obtained during field measurements in Yopougon. ...High emissions of black carbon (BC) from vehicles are observed at major road intersections, in areas surrounding industrial zones and on highways. Highest emission values from road traffic are observed for carbon monoxide (CO) (14.8 t/d) and nitrogen oxides (NOx) (7.9 t/d), usually considered as the major traffic pollution tracers. Furthermore, peak values of CO emissions due to personal cars (PCs) are mainly linked to the old age of the vehicle fleet with high emission factors. The highest emitting type of vehicle for BC on the highway is PC (70.2%), followed by inter-communal taxis (TAs) (13.1%), heavy vehicles (HVs) (9.8%), minibuses (GBs) (6.4%) and intra-communal taxis (WRs) (0.4%). While for organic carbon (OC) emissions on the main roads, PCs represent 46.7%, followed by 20.3% for WRs, 14.9% for TAs, 11.4% for GB and 6.7% for HVs. This work provides new key information on local pollutant emissions and may be useful to guide mitigation strategies such as modernizing the vehicle fleet and reorganizing public transportation, to reduce emissions and improve public health.
The physico-chemical characteristics of particulate matter (PM) in African cities remain poorly known due to scarcity of observation networks. Magnetic parameters of PM are robust proxies for the ...emissions of Fe-bearing particles. This study reports the first magnetic investigation of PM2.5 (PM with aerodynamic size below 2.5 μm) in Africa performed on weekly PM2.5 filters collected in Abidjan (Ivory Coast) and Cotonou (Benin) between 2015 and 2017. The magnetic mineralogy is dominated by magnetite-like low coercivity minerals. Mass normalized SIRM are 1.65 × 10−2 A m2 kg−1 and 2.28 × 10−2 A m2 kg−1 for Abidjan and Cotonou respectively. Hard coercivity material (S-ratio = 0.96 and MDF = 33 mT) is observed during the dry dusty season. Wood burning emits less iron oxides by PM2.5 mass when compared to traffic sources. PM2.5 magnetic granulometry has a narrow range regardless of the site or season. The excellent correlation between the site-averaged element carbon concentrations and SIRM suggests that PM2.5 magnetic parameters are linked to primary particulate emission from combustion sources.
In West African cities, the impacts of the air quality on the health of the population is expected to increase significantly in the near future. For the first time to our knowledge, we conducted a ...high-resolution modeling study over Abidjan (Côte d’Ivoire) using the WRF-Chem model and the simplified GOCART model to simulate carbonaceous aerosols BC and OC, sulfate, dust, sea salt, PM2.5, and PM10. The simulations were carried out during January and February 2019, a period over which there are databases of observations available. The DACCIWA inventory provided anthropogenic emissions at the regional scale, whereas a new emission inventory has been developed for the city of Abidjan. In 2019, the emissions were 4986.8 Gg for BC, 14,731.4 Gg for OC, and 7751.6 Gg for SO2. Domestic fires were the primary OC source (7719.5 Gg), while road traffic was the largest BC emitter (2198.8 Gg). Our modeling results generally overestimate urban particle concentrations, despite having a better agreement for those based on the inventory of the city of Abidjan. Modeled concentrations of BC are higher in administrative centers due to road traffic, while OC concentrations are significant in densely populated neighborhoods.
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.
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 surface PM2.5 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 µg m−3) are associated with the advection of mineral dust in the heart of the dry season (December–February). Annual means are around 30 µg m−3, and 80 % of days in the winter dry season have a value above 35 µg m−3, while concentrations remain below 16 µg m−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.
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.
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