Effect of ammonia on fine-particle pH in agricultural regions of China: comparison between urban and rural sites
<p>Particle acidity is a fundamental property that affects atmospheric particulate chemistry. Synchronous online monitoring was performed at two urban sites, Zhengzhou (U-ZZ) and Anyang (U-AY), and three rural sites, Anyang (R-AY), Xinxiang (R-XX), and Puyang (R-PY) in Henan Province, during a...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/20/2719/2020/acp-20-2719-2020.pdf |
| Summary: | <p>Particle acidity is a fundamental property that affects atmospheric particulate chemistry. Synchronous online monitoring was performed at two urban
sites, Zhengzhou (U-ZZ) and Anyang (U-AY), and three rural sites, Anyang (R-AY), Xinxiang (R-XX), and Puyang (R-PY) in Henan Province,
during a haze episode to investigate the pH value and its driving factors in the agricultural regions of China. The pH values of particles
calculated by ISORROPIA-II model at rural sites were slightly higher than those at urban sites, with the median (min–max) values of 5.2 (4.8–6.9,
R-PY), 5.1 (4.7–6.5, R-AY), 4.9 (4.1–6.8, R-XX), 4.8 (3.9–5.9, U-AY), and 4.5 (3.8–5.2, U-ZZ). Sensitivity tests show that <span class="inline-formula"><i>T</i>NH<sub><i>x</i></sub></span> (total
ammonium, gas <span class="inline-formula">+</span> aerosol) followed by total sulfate were the most important factors that influenced the predicted pH. Generally, particle pH
increased with a cation increase and decreases in anions, temperature, and relative humidity. Similar pH values (<span class="inline-formula">∼3.0</span>) at the
required <span class="inline-formula">NH<sub><i>x</i></sub></span> concentrations for the five sites indicated that the presence of excess <span class="inline-formula">NH<sub><i>x</i></sub></span> was likely important for the lower acidity
of <span class="inline-formula">PM<sub>2.5</sub></span> during the severe haze episodes in this region. Moreover, the concentrations of excess <span class="inline-formula">NH<sub><i>x</i></sub></span> may drive the higher
pH values at rural sites, because of the higher excess <span class="inline-formula">NH<sub><i>x</i></sub></span> concentrations at rural sites than those at urban sites. The underlying
influence of regional transport on local particle pH cannot be neglected, as it differs the chemical components of <span class="inline-formula">PM<sub>2.5</sub></span> and meteorological
conditions. Air masses transported from rural and agricultural regions may enhance the particle pH value in urban aerosols given the high pH of
particles and high ammonia levels. These results suggest that ammonia is urgently needed to be involved in the regional strategy for the improvement
of air quality in China.</p> |
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| ISSN: | 1680-7316 1680-7324 |