Journal
NATURE GEOSCIENCE
Volume 14, Issue 6, Pages 389-+Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41561-021-00726-z
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Funding
- Harvard-NUIST Joint Laboratory for Air Quality and Climate
- Samsung PM2.5 Strategic Research Program
- National Key Research and Development Program of China [2019YFA0606804]
- NASA [NNX17AG35G]
- Beijing Municipal Natural Science Foundation [8202049]
- Samsung Advanced Institute of Technology
- NASA [NNX17AG35G, 1001971] Funding Source: Federal RePORTER
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The concentration of fine particulate matter (PM2.5) in China decreased by 30-50% from 2013 to 2018 due to emission controls, but the nitrate component did not decrease effectively. Increased particulate nitrate concentration during winter haze pollution events is attributed to the particulate fraction transitioning from gaseous nitric acid. Reducing ammonia emissions is suggested as an effective method to decrease the nitrate component of fine particulate matter pollution in the North China Plain.
The concentration of fine particulate matter (PM2.5) across China has decreased by 30-50% over the period 2013-2018 due to stringent emission controls. However, the nitrate component of PM2.5 has not responded effectively to decreasing emissions of nitrogen oxides and has actually increased during winter haze pollution events in the North China Plain. Here, we show that the GEOS-Chem atmospheric chemistry model successfully simulates the nitrate concentrations and trends. We find that winter mean nitrate would have increased over 2013-2018 were it not for favourable meteorology. The principal cause of this nitrate increase is weaker deposition. The fraction of total inorganic nitrate as particulate nitrate instead of gaseous nitric acid over the North China Plain in winter increased from 90% in 2013 to 98% in 2017, as emissions of nitrogen oxides and sulfur dioxide decreased while ammonia emissions remained high. This small increase in the particulate fraction greatly slows down deposition of total inorganic nitrate and hence drives the particulate nitrate increase. Our results suggest that decreasing ammonia emissions would decrease particulate nitrate by driving faster deposition of total inorganic nitrate. Decreasing nitrogen oxide emissions is less effective because it drives faster oxidation of nitrogen oxides and slower deposition of total inorganic nitrate. Reduction of ammonia emissions may be effective in reducing the nitrate component of fine particulate matter air pollution across the North China Plain, according to the simulation of nitrate trends using the GEOS-Chem atmospheric chemistry model.
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