A 15-year record (2001–2015) of the ratio of nitrate to non-sea-salt sulfate in precipitation over East Asia
Acidifying species in precipitation can have severe impacts on ecosystems. The chemical composition of precipitation is directly related to the amount of precipitation; accordingly, it is difficult to identify long-term variation in chemical concentrations. The ratio of the nitrate (NO<sub>...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/2835/2018/acp-18-2835-2018.pdf |
| Summary: | Acidifying species in precipitation can have severe impacts on ecosystems.
The chemical composition of precipitation is directly related to the amount
of precipitation; accordingly, it is difficult to identify long-term
variation in chemical concentrations. The ratio of the nitrate (NO<sub>3</sub><sup>−</sup>)
to non-sea-salt sulfate (nss-SO<sub>4</sub><sup>2−</sup>) concentration in precipitation on
an equivalent basis (hereinafter, <i>Ratio</i>) is a useful index to
investigate the relative contributions of these acidifying species. To
identify the long-term record of acidifying species in precipitation over
East Asia, the region with the highest emissions worldwide, we compiled
ground-based observations of the chemical composition of precipitation over
China, Korea, and Japan from 2001 to 2015 based on the Acid Deposition
Monitoring Network in East Asia (EANET). The spatial coverage was limited,
but additional monitoring data for Japan, southern China, and northern China
around Beijing were utilized. The period of analysis was divided into three
phases: Phase I (2001–2005), Phase II (2006–2010), and Phase III
(2011–2015). The behaviors of NO<sub>3</sub><sup>−</sup> and nss-SO<sub>4</sub><sup>2−</sup>
concentrations and hence the <i>Ratio</i> in precipitation were related to
these precursors. The anthropogenic NO<sub><i>x</i></sub> and SO<sub>2</sub> emissions and the
NO<sub><i>x</i></sub> ∕ SO<sub>2</sub> emission ratio were analyzed. Further, satellite
observations of the NO<sub>2</sub> and SO<sub>2</sub> column density to capture the
variation in emissions were applied. We found that the long-term trend in the
NO<sub>3</sub><sup>−</sup> concentration in precipitation was not related to the variation
in NO<sub><i>x</i></sub> emission and the NO<sub>2</sub> column. In comparison, the
nss-SO<sub>4</sub><sup>2−</sup> concentration in precipitation over China, Korea, and Japan
was partially connected to the changes in SO<sub>2</sub> emissions from China, but
the trends were not significant. The long-term trends of <i>Ratio</i> over
China, Korea, and Japan were nearly flat during Phase I, increased
significantly during Phase II, and were essentially flat again during
Phase III. This variation in <i>Ratio</i> in East Asia clearly corresponded
to the NO<sub><i>x</i></sub> ∕ SO<sub>2</sub> emission ratio and the NO<sub>2</sub> ∕ SO<sub>2</sub>
column ratio in China. The initial flat trend during Phase I was due to
increases in both NO<sub><i>x</i></sub> and SO<sub>2</sub> emissions in China, the significantly
increasing trend during Phase II was triggered by the increase in NO<sub><i>x</i></sub>
emissions and decrease in SO<sub>2</sub> emissions in China, and the return to a
flat trend during Phase III was caused by declines in both NO<sub><i>x</i></sub> and
SO<sub>2</sub> emissions in China. These results suggest that emissions in China
had a significant impact not only on China but also on downwind precipitation
chemistry during the 15-year period of 2001–2015. In terms of wet
deposition, the NO<sub>3</sub><sup>−</sup> wet deposition over China, Korea, and Japan did
not change dramatically, but the nss-SO<sub>4</sub><sup>2−</sup> wet deposition declined
over China, Korea, and Japan from Phase II to III. These declines were caused
by a strong decrease in the nss-SO<sub>4</sub><sup>2−</sup> concentration in precipitation
accompanied by a reduction in SO<sub>2</sub> emission from China, which
counteracted the increase in precipitation. These findings indicated that the
acidity of precipitation shifted from sulfur to nitrogen. |
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| ISSN: | 1680-7316 1680-7324 |