Particulate organic nitrates in eastern China: variation characteristics and effects of anthropogenic activities

Abstract. Particulate organic nitrates (PONs) constitute a substantial fraction of secondary organic aerosols and have important effects on the reactive nitrogen budget and air quality. Laboratory studies have revealed the non-negligible influence of the interactions between anthropogenic pollutants and biogenic volatile organic compounds (BVOCs) on the formation of PONs. In this study, the contents of specific PONs, including monoterpene hydroxyl nitrate (MHN215), pinene keto nitrate (PKN229), limonene di-keto nitrate (LDKN247), oleic acid keto nitrate (OAKN359), oleic acid hydroxyl nitrate (OAHN361), and pinene sulfate organic nitrate (PSON295), in fine particulate matters at four rural and urban sites in eastern China were determined, and the variation characteristics of PONs and the impacts of human activities on PONs formation were investigated. The average concentration of PONs ranged from 116 to 548 ng m⁻³ at these four sites. PONs were present in higher levels in summer than in other seasons, owing to the high emissions of precursors and intensive photochemical activities in this hottest season. Among the six species of PONs, MHN215 was dominant. In addition, the proportion of OAKN359 in PONs in urban areas was much higher than that in the rural site, indicating that OAKN359 primarily originated from anthropogenic activities. Slight diurnal differences existed in the concentration and secondary formation of specific PONs and varied with locations, seasons, and precursor VOCs. The measurement results showed that PONs in North China were clearly influenced by coal combustion and biomass burning, while meteorological conditions and biogenic emissions were the dominant contributing factors in the South China. Biomass burning significantly enhanced the formation of PONs due to the elevated concentrations of ozone and the released BVOCs. Sulfur dioxide (SO₂) emitted from coal combustion was able to react rapidly with Criegee intermediates, the reaction products of BVOCs with ozone, to produce PONs at high rates, suggesting that there is a substantially greater role played by SO₂ in organic nitrate chemistry than has previously been assumed.