4 research outputs found
Trends and seasonal variability in ammonia across major biomes in western and central Africa inferred from long-term series of ground-based and satellite measurements
Ammonia (NH3) is the most abundant alkaline
component in the atmosphere. Changes in NH3 concentrations have
important implications for atmospheric chemistry, air quality, and ecosystem
integrity. We present a long-term ammonia (NH3) assessment in the
western and central African regions within the framework of the International
Network to study Deposition and Atmospheric chemistry in Africa (INDAAF)
programme. We analyse seasonal variations and trends in NH3
concentrations and total column densities along an African ecosystem
transect spanning dry savannas in Banizoumbou, Niger, and Katibougou, Mali;
wet savannas in Djougou, Benin, and Lamto, Côte d'Ivoire; and forests in Bomassa, Republic of the Congo, and Zoétélé, Cameroon. We use a
21-year record of observations (1998–2018) from INDAAF passive samplers and an 11-year record of observations (2008–2018) of atmospheric vertical column densities from the Infrared Atmospheric Sounding Interferometer (IASI) to evaluate NH3 ground-based concentrations and total column densities,
respectively. Climatic data (air temperature, rainfall amount, and leaf area
index), as well as ammonia emission data of biomass combustion from the
fourth version of the Global Fire Emissions Database (GFED4) and
anthropogenic sources from the Community Emissions Data System (CEDS), were
compared with total NH3 concentrations and total columns over the same
periods. Annual mean ground-based NH3 concentrations are around 5.7–5.8 ppb in dry savannas, 3.5–4.7 ppb in wet savannas, and 3.4–5.6 ppb in forests. Annual IASI NH3 total column densities are 10.0–10.7 × 1015 molec. cm−2 in dry savanna, 16.0–20.9 × 1015 molec. cm−2 in wet
savanna, and 12.4–13.8 × 1015 molec. cm−2 in forest stations. Non-parametric statistical Mann–Kendall trend tests applied to annual data show that ground-based NH3 concentrations increase at Bomassa (+2.56 % yr−1) but decrease at Zoétélé (−2.95 % yr−1) over the 21-year period. The 11-year period of IASI NH3 total column density measurements show yearly increasing trends at Katibougou (+3.46 % yr−1), Djougou (+2.24 % yr−1), and Zoétélé (+3.42 % yr−1). From the outcome of our
investigation, we conclude that air temperature, leaf area index, and
rainfall combined with biomass burning, agricultural, and residential
activities are the key drivers of atmospheric NH3 in the INDAAF
stations. The results also show that the drivers of trends are (1)Â agriculture in the dry savanna of Katibougou; (2)Â air temperature and agriculture in the wet savanna of Djougou and Lamto; and (3)Â leaf area index, air temperature, residential, and agriculture in the forest of Bomassa.</p
A pilot study of gaseous pollutants' measurement (NO<sub>2</sub>, SO<sub>2</sub>, NH<sub>3</sub>, HNO<sub>3</sub> and O<sub>3</sub>) in Abidjan, Côte d'Ivoire: contribution to an overview of gaseous pollution in African cities
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)Â to define national standards and to better control the
pollutants emissions and (2)Â to investigate the impact on the health
of the growing population in developing African countries
Analysis of trends and seasonal variations of nitrogen dioxide and nitric acid concentrations measured at six rural sites in Africa from 1998 to 2015
International audienc
Mass concentration, optical depth and carbon composition of particulate matter in the major southern West African cities of Cotonou (Benin) and Abidjan (Côte d'Ivoire)
Air quality degradation is a major issue in the large conurbations on
the shore of the Gulf of Guinea. We present for the first time
PM2.5 time series collected in Cotonou, Benin, and Abidjan,
Côte d'Ivoire, from February 2015 to March 2017. Measurements were
performed in the vicinity of major combustion aerosol sources:
Cotonou/traffic (CT), Abidjan/traffic (AT), Abidjan/landfill (AL) and
Abidjan/domestic fires (ADF). We report the weekly PM2.5 mass and
carbonaceous content as elemental (EC) and organic (OC) carbon
concentrations. We also measure the aerosol optical depth (AOD) and the
Ångström exponent in both cities. The average PM2.5 mass
concentrations were 32 ± 32, 32 ± 24 and
28 ± 19 µg m−3 at traffic sites CT and AT and landfill
site AL, respectively. The domestic fire site shows a concentration of
145 ± 69 µg m−3 due to the contribution of smoking and
roasting activities. The highest OC and EC concentrations were also measured
at ADF at 71 ± 29 and 15 ± 9 µg m−3,
respectively, while the other sites present OC concentration between 8 and
12 µg m−3 and EC concentrations between 2 and
7 µg m−3. The OC ∕ EC ratio is 4.3 at CT and 2.0 at AT.
This difference highlights the influence of two-wheel vehicles using gasoline
in Cotonou compared to that of four-wheel vehicles using diesel fuel in
Abidjan. AOD was rather similar in both cities, with a mean value of 0.58 in
Cotonou and of 0.68 in Abidjan. The seasonal cycle is dominated by the large
increase in surface mass concentration and AOD during the long dry season
(December–February) as expected due to mineral dust advection and biomass
burning activities. The lowest concentrations are observed during the short
dry season (August–September) due to an increase in surface wind speed
leading to a better ventilation. On the other hand, the high
PM2.5 ∕ AOD ratio in the short wet season (October–November)
indicates the stagnation of local pollution