Northwestward cropland expansion and growing urea-based fertilizer use enhanced NH<sub>3</sub> emission loss in the contiguous United States
<p>The increasing demands of food and biofuel have promoted cropland expansion and nitrogen (N) fertilizer enrichment in the United States over the past century. However, the role of such long-term human activities in influencing the spatiotemporal patterns of ammonia (NH<span class="i...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/20/11907/2020/acp-20-11907-2020.pdf |
| Summary: | <p>The increasing demands of food and biofuel have promoted cropland
expansion and nitrogen (N) fertilizer enrichment in the United States over
the past century. However, the role of such long-term human activities in
influencing the spatiotemporal patterns of ammonia (NH<span class="inline-formula"><sub>3</sub></span>) emission
remains poorly understood. Based on an empirical model and time-series
gridded datasets including temperature, soil properties, N fertilizer
management, and cropland distribution history, we have quantified monthly fertilizer-induced NH<span class="inline-formula"><sub>3</sub></span> emission across the contiguous US from 1900 to 2015. Our results show that N-fertilizer-induced NH<span class="inline-formula"><sub>3</sub></span> emission in the US has increased from <span class="inline-formula"><50</span> Gg N yr<span class="inline-formula"><sup>−1</sup></span> before the 1960s to 641 Gg N yr<span class="inline-formula"><sup>−1</sup></span> in 2015, for which corn and spring wheat are the dominant contributors. Meanwhile, urea-based fertilizers gradually grew to the largest NH<span class="inline-formula"><sub>3</sub></span> emitter and accounted for 78 % of the total increase
during 1960–2015. The factorial contribution analysis indicates that the
rising N fertilizer use rate dominated the NH<span class="inline-formula"><sub>3</sub></span> emission increase since 1960, whereas the impacts of temperature, cropland distribution and
rotation, and N fertilizer type varied among regions and over periods.
Geospatial analysis reveals that the hot spots of NH<span class="inline-formula"><sub>3</sub></span> emissions have
shifted from the central US to the Northern Great Plains from 1960 to 2015. The increasing NH<span class="inline-formula"><sub>3</sub></span> emissions in the Northern Great Plains have been found to closely correlate to the elevated NH<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="9ae7496f73369cba691a3bcfb358d1a5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-11907-2020-ie00001.svg" width="8pt" height="15pt" src="acp-20-11907-2020-ie00001.png"/></svg:svg></span></span> deposition in this region over the last 3 decades. This study shows that April, May, and June
account for the majority of NH<span class="inline-formula"><sub>3</sub></span> emission in a year. Interestingly, the
peak emission month has shifted from May to April since the 1960s. Our
results imply that the northwestward corn and spring wheat expansion and
growing urea-based fertilizer uses have dramatically altered the spatial
pattern and temporal dynamics of NH<span class="inline-formula"><sub>3</sub></span> emission, impacting air pollution
and public health in the US.</p> |
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| ISSN: | 1680-7316 1680-7324 |