State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China; CMA-NKU Cooperative Laboratory for Atmospheric Environment-Health Research, Tianjin 300000, China; Meteorological and Environmental Center of Tianjin, Tianjin 300074, China.
State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China; CMA-NKU Cooperative Laboratory for Atmospheric Environment-Health Research, Tianjin 300000, China.
Sci Total Environ. 2021 Mar 10;759:143540. doi: 10.1016/j.scitotenv.2020.143540. Epub 2020 Nov 7.
Haze pollution characteristics and PM chemical composition were distinctive in different air humidity-dependent haze episodes in winter of North China Plain (NCP). The impact of air humidity on particulate chemical composition was investigated based on the in situ observation in winter of 2017-2018 in Tianjin. Relative humidity (RH) and absolute humidity affect the secondary aerosol generation in different ways. Particularly, nitrate changes more obviously with absolute humidity, while sulfate changes more obviously with RH. In the daytime, at certain conditions, high water vapor content, O concentration and stronger solar radiation may promote the gas-phase oxidation of NO by the addition of OH formed though O photolysis, especially during the transition periods between winter and autumn or spring. Whereas in the nighttime, temperature drop generated the high RH, which was favorable for the gas-particle portioning of HNO and the occurrence of the NO heterogeneous hydrolysis reaction. At lower temperature and higher RH (T < 0 °C, RH > 80%) condition, SO mass fraction was relatively higher. Lower temperature can result in more SO dissolved in equilibrium and the relatively higher initial aerosol pH, which both generate faster aqueous oxidation rate. Given the currently low SO concentration in the regional scale, the meteorological condition in which the occurrence of sulfate formation through aqueous reaction may be more stringent.
在中国北方冬季，霾污染特征和 PM 化学组成在不同湿度依赖型霾事件中存在显著差异。本研究基于 2017-2018 年冬季在天津进行的现场观测，探讨了空气湿度对颗粒物化学组成的影响。相对湿度（RH）和绝对湿度以不同的方式影响二次气溶胶的生成。特别是，硝酸盐随绝对湿度的变化更为明显，而硫酸盐随 RH 的变化更为明显。在白天，在某些条件下，高水汽含量、O 浓度和更强的太阳辐射可能通过 O 光解形成的 OH 促进 NO 的气相氧化，特别是在冬春或秋冬过渡期间。而在夜间，温度下降会产生高 RH，有利于 HNO 的气粒分配和 NO 非均相水解反应的发生。在较低的温度和较高的 RH（T < 0°C，RH > 80%）条件下，SO 质量分数相对较高。较低的温度会导致更多的 SO 溶解在平衡中，以及相对较高的初始气溶胶 pH 值，这两者都会产生更快的水相氧化速率。鉴于目前区域尺度上 SO 浓度较低，通过水相反应形成硫酸盐的气象条件可能更为严格。
