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
<p><span id="page9474"/>Ammonia (NH<span class="inline-formula"><sub>3</sub></span>) is the most abundant alkaline component in the atmosphere. Changes in NH<span class="inline-formula"><sub>3</sub></span> conc...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/9473/2023/acp-23-9473-2023.pdf |
| Summary: | <p><span id="page9474"/>Ammonia (NH<span class="inline-formula"><sub>3</sub></span>) is the most abundant alkaline
component in the atmosphere. Changes in NH<span class="inline-formula"><sub>3</sub></span> concentrations have
important implications for atmospheric chemistry, air quality, and ecosystem
integrity. We present a long-term ammonia (NH<span class="inline-formula"><sub>3</sub></span>) 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 NH<span class="inline-formula"><sub>3</sub></span>
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 NH<span class="inline-formula"><sub>3</sub></span> 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 NH<span class="inline-formula"><sub>3</sub></span> concentrations and total columns over the same
periods. Annual mean ground-based NH<span class="inline-formula"><sub>3</sub></span> 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 NH<span class="inline-formula"><sub>3</sub></span> total column densities are 10.0–10.7 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>15</sup></span> molec. cm<span class="inline-formula"><sup>−2</sup></span> in dry savanna, 16.0–20.9 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>15</sup></span> molec. cm<span class="inline-formula"><sup>−2</sup></span> in wet
savanna, and 12.4–13.8 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>15</sup></span> molec. cm<span class="inline-formula"><sup>−2</sup></span> in forest stations. Non-parametric statistical Mann–Kendall trend tests applied to annual data show that ground-based NH<span class="inline-formula"><sub>3</sub></span> concentrations increase at Bomassa (<span class="inline-formula">+</span>2.56 % yr<span class="inline-formula"><sup>−1</sup></span>) but decrease at Zoétélé (<span class="inline-formula">−</span>2.95 % yr<span class="inline-formula"><sup>−1</sup></span>) over the 21-year period. The 11-year period of IASI NH<span class="inline-formula"><sub>3</sub></span> total column density measurements show yearly increasing trends at Katibougou (<span class="inline-formula">+</span>3.46 % yr<span class="inline-formula"><sup>−1</sup></span>), Djougou (<span class="inline-formula">+</span>2.24 % yr<span class="inline-formula"><sup>−1</sup></span>), and Zoétélé (<span class="inline-formula">+</span>3.42 % yr<span class="inline-formula"><sup>−1</sup></span>). 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 NH<span class="inline-formula"><sub>3</sub></span> in the INDAAF
stations. The results also show that the drivers of trends are (1) agriculture in the dry savanna of Katibougou; (2) air temperature and agriculture in the wet savanna of Djougou and Lamto; and (3) leaf area index, air temperature, residential, and agriculture in the forest of Bomassa.</p> |
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| ISSN: | 1680-7316 1680-7324 |