Beijing Key Laboratory of Farmland Soil Pollution Prevention and Remediation, College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, China Agricultural University, Beijing 100193, China.
Beijing Key Laboratory of Farmland Soil Pollution Prevention and Remediation, College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, China Agricultural University, Beijing 100193, China.
J Environ Sci (China). 2022 Dec;122:83-91. doi: 10.1016/j.jes.2021.09.031. Epub 2022 Feb 1.
We investigated variations of PM and water-soluble inorganic ions chemical characteristics at nine urban and rural sites in China using ground-based observations. From 2015 to 2019, mean PM concentration across all sites decreased by 41.9 µg/m with a decline of 46% at urban sites and 28% at rural sites, where secondary inorganic aerosol (SIAs) contributed to 21% (urban sites) and 17% (rural sites) of the decreased PM. SIAs concentrations underwent a decline at urban locations, while sulfate (SO), nitrate (NO), and ammonium (NH) decreased by 49.5%, 31.3% and 31.6%, respectively. However, only SO decreased at rural sites, NO increased by 21% and NH decreased slightly. Those changes contributed to an overall SIAs increase in 2019. Higher molar ratios of NO to SO and NH to SO were observed at urban sites than rural sites, being highest in the heavily polluted days. Mean molar ratios of NH/NH were higher in 2019 than 2015 at both urban and rural sites, implying increasing NH remained as free NH. Our observations indicated a slower transition from sulfate-driven to nitrate-driven aerosol pollution and less efficient control of NO than SO related aerosol formation in rural regions than urban regions. Moreover, the common factor at urban and rural sites appears to be a combination of lower SO levels and an increasing fraction of NO to PM under NH-rich conditions. Our findings imply that synchronous reduction in NO and NH emissions especially rural areas would be effective to mitigate NO-driven aerosol pollution.
我们利用地面观测研究了中国九个城乡站点的 PM 和水溶性无机离子化学特征的变化。2015 年至 2019 年，所有站点的 PM 浓度平均值下降了 41.9µg/m，城市站点下降了 46%，农村站点下降了 28%，其中二次无机气溶胶（SIA）对 PM 的降低贡献了 21%（城市站点）和 17%（农村站点）。SIA 浓度在城市地区下降，而硫酸盐（SO）、硝酸盐（NO）和铵（NH）分别下降了 49.5%、31.3%和 31.6%。然而，只有农村站点的 SO 下降，NO 增加了 21%，NH 略有下降。这些变化导致 2019 年 SIA 总体增加。在城市地区观察到的 NO 与 SO 和 NH 与 SO 的摩尔比高于农村地区，在污染严重的日子里最高。与 2015 年相比，2019 年城市和农村地区的 NH/NH 平均摩尔比均较高，这表明增加的 NH 仍为游离 NH。我们的观察表明，与城市地区相比，农村地区从硫酸盐驱动到硝酸盐驱动的气溶胶污染的转变较慢，对 NO 的控制效率低于 SO 相关气溶胶的形成。此外，城市和农村地区的共同因素似乎是在 NH 丰富的条件下，SO 水平降低和 NO 与 PM 的比例增加。我们的研究结果表明，特别是在农村地区，同步减少 NO 和 NH 的排放将有效缓解由 NO 驱动的气溶胶污染。
