Abstract Nitrate has become the most important hydrophilic chemical component in PM2.5 during serious air pollution periods in urban areas of the Pearl River Delta (PRD) region of south China, but there is a lack of fully understanding of its formation mechanisms and controlling factors, especially during daytime nitrate episodes. To fill the knowledge gap, water-soluble inorganic ions in PM2.5 and trace gases including SO2, HNO3, NH3, NOx and O3, particle size distribution, vertical profile of aerosol backscatter density, and ground-level and vertical profiles of key meteorological variables were simultaneously measured at high time resolution in urban Guangzhou of the PRD. The remarkably enhanced nitrate mass concentrations observed at the surface-level during daytime were identified to be caused by strong boundary-layer turbulent mixing of residual aerosols produced from evaporation of low-level shallow stratocumulus clouds. This finding may have important implications on the sources of secondary inorganic aerosols in this and other similar cloudy regions.

中文翻译：

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云过程的观测证据导致白天城市大气中硝酸盐升高

摘要 在华南珠江三角洲（PRD）城市地区空气污染严重时期，硝酸盐已成为PM2.5中最主要的亲水化学成分，但对其形成机制和控制因素缺乏充分认识。 ，尤其是在白天硝酸盐发作期间。PM2.5中水溶性无机离子及SO2、HNO3、NH3、NOx、O3等痕量气体、粒径分布、气溶胶后向散射密度垂直剖面、重点气象地表和垂直剖面等填补知识空白。在珠三角广州市区以高时间分辨率同时测量变量。白天在地表观察到的硝酸盐质量浓度显着增加，被认为是由低层浅层积云蒸发产生的残余气溶胶的强烈边界层湍流混合引起的。这一发现可能对这个地区和其他类似多云地区的二次无机气溶胶的来源具有重要意义。