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Ammonia-rich environment enhances nitrate formation in PM2.5 in a megacity of the Yangtze River Delta, China
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DOI：10.1007/s10874-025-09484-3.png)
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Abstract
En 中文
Nitrate (NO3–) levels in air pollution have shown a sustained increase across eastern China. However, the key drivers behind rising surface NO3– concentrations remain unclear, posing challenges for targeted pollution control strategies. PM2.5 samples were collected from September 2015 to August 2016 at both urban and suburban sites in Nanjing, a megacity in the Yangtze River Delta (YRD), for compositional analysis and source apportionment. The measured annual mean PM2.5 concentration was 96.8 ± 46.0 µg m–3. The positive matrix factorization model identified four primary PM2.5 sources in Nanjing: secondary nitrate (19.4%), secondary sulfate (36.8%), coal and biomass burning (40.6%), and industrial emissions (3.2%). Water-soluble secondary inorganic aerosols (NO3–, SO42–, NH4+) dominated PM2.5 composition, accounting for 92.7% of ionic components and 37.0% of total mass. NO3– concentrations exhibited significant increases in both absolute and relative terms as PM2.5 pollution levels rose, suggesting its important role in PM2.5 pollution. The results indicate that NO3– formation is enhanced under ammonia-rich conditions with low temperatures, high humidity, and elevated acidity. Policy-driven reductions in SO2 and NOx, without simultaneous NH3 control, may have contributed to ammonia-rich conditions that facilitated NO3– formation, leading to NO3–-dominated PM2.5 pollution in the YRD. Therefore, our results indicate that coordinated control of both nitrogen oxides and ammonia emissions may be necessary to mitigate NO3–-driven PM2.5pollution. PM2.5 concentrations and sources in Nanjing were investigated from many perspectives. Precursors, meteorology, aerosol acidity impact secondary inorganic aerosol formation. Nitrate drives PM2.5formation and as the dominant component during severe pollution period. Ammonia-rich environment enhances nitrate formation in PM2.5.
Keywords:
PM 2.5
Secondary inorganic aerosol
Source apportionment
Nitrate
Sulfate
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