Changes in biomass burning, wetland extent, or agriculture drive atmospheric NH<sub>3</sub> trends in select African regions
<p>Atmospheric ammonia (NH<span class="inline-formula"><sub>3</sub></span>) is a precursor to fine particulate matter and a source of nitrogen (N) deposition that can adversely affect ecosystem health. The main sources of NH<span class="inline-formula&...
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| Autores principales: | , , , , , , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/ced0df0358b64428b48f897b744741f9 |
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| Sumario: | <p>Atmospheric ammonia (NH<span class="inline-formula"><sub>3</sub></span>) is a precursor to fine particulate matter and
a source of nitrogen (N) deposition that can adversely affect ecosystem
health. The main sources of NH<span class="inline-formula"><sub>3</sub></span> – agriculture and biomass burning – are
undergoing are or expected to undergo substantial changes in Africa. Although
evidence of increasing NH<span class="inline-formula"><sub>3</sub></span> over parts of Africa has been observed, the
mechanisms behind these trends are not well understood. Here we use
observations of atmospheric NH<span class="inline-formula"><sub>3</sub></span> vertical column densities (VCDs) from
the Infrared Atmospheric Sounding Interferometer (IASI) along with other
satellite observations of the land surface and atmosphere to evaluate how
NH<span class="inline-formula"><sub>3</sub></span> concentrations have changed over Africa from 2008 through 2018, and
what has caused those changes. In West Africa NH<span class="inline-formula"><sub>3</sub></span> VCDs are observed to
increase during the late dry season, with increases of over 6 % yr<span class="inline-formula"><sup>−1</sup></span>
in Nigeria during February and March (<span class="inline-formula"><i>p</i><i><</i>0.01</span>). These positive
trends are associated with increasing burned area and CO trends during these
months, likely related to agricultural preparation. Increases are also
observed in the Lake Victoria basin region, where they are associated with
expanding agricultural area. In contrast, NH<span class="inline-formula"><sub>3</sub></span> VCDs declined over the
Sudd wetlands in South Sudan by over 1.5 % yr<span class="inline-formula"><sup>−1</sup></span>, though not
significantly (<span class="inline-formula"><i>p</i>=0.28</span>). Annual maxima in NH<span class="inline-formula"><sub>3</sub></span> VCDs in South Sudan
occur during February through May and are associated with the drying of
temporarily flooded wetland soils, which favor emissions of NH<span class="inline-formula"><sub>3</sub></span>. The
change in mean NH<span class="inline-formula"><sub>3</sub></span> VCDs over the Sudd is strongly correlated with
variation in wetland extent in the Sudd: in years when more area remained
flooded during the dry season, NH<span class="inline-formula"><sub>3</sub></span> VCDs were lower (<span class="inline-formula"><i>r</i>=0.64</span>,
<span class="inline-formula"><i>p</i><i><</i>0.05</span>). Relationships between biomass burning and NH<span class="inline-formula"><sub>3</sub></span> may be
observed when evaluating national-scale statistics: countries with the
highest rates of increasing NH<span class="inline-formula"><sub>3</sub></span> VCDs also had high rates of growth in
CO VCDs; burned area displayed a similar pattern, though not significantly.
Livestock numbers were also higher in countries with intermediate or high
rates of NH<span class="inline-formula"><sub>3</sub></span> VCD growth. Fertilizer use in Africa is currently low but
growing; implementing practices that can limit NH<span class="inline-formula"><sub>3</sub></span> losses from
fertilizer as agriculture is intensified may help mitigate impacts on health
and ecosystems.</p> |
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