Xiao Zhi-Mei, Wu Ting, Wei Yu-Ting, Xu Hong, Li Li-Wei, Li Peng, Chen Kui, Deng Xiao-Wen
Tianjin Eco-Environmental Monitoring Center, Tianjin 300191, China.
Tianjin Ecological Environment Comprehensive Guarantee Center, Tianjin 300191, China.
Huan Jing Ke Xue. 2021 Jun 8;42(6):2616-2625. doi: 10.13227/j.hjkx.202010119.
To study the formation and approaches to controlling secondary nitrate in PM, the ionic compositions of PM, pH of aerosols, variations in NH-NH and HNO-NO concentrations, and the joint NH/HNO sensitivity regime map of ammonium nitrate were investigated based on high-resolution online monitoring data for an urban site in central Tianjin from 2018 to 2019. The results showed that the average concentration of PM was 58μg·m, and the main ionic compositions of PM were nitrate (NO), ammonium (NH), sulfate (SO), Cl, and K with corresponding mass percentages of 18.4%, 11.6%, 10.3%, 3.3%, and 2.6%, respectively. Concentrations of PM and the main components were relatively high during the heating season and relatively low during the non-heating season. The aerosols were weakly acidity with an average pH of 5.21; pH was higher in spring and winter and lower in summer and autumn, and diurnal variations pH were lower in the morning (00:00-08:00) and slightly higher at other times. The concentrations of NH(g) (gas NH) and HNO(g) (gas HNO) were 16.7μg·mand 1.2μg·m, respectively. The concentrations of NH(g) were relatively higher from April to September and lower from October to February of the following year. HNO(g) concentrations did not show any clear monthly pattern. Except during the summer, NH(g) concentrations were higher in the morning and evening, and HNO(g) concentrations were higher during the day. No clear linear relationships were observed between the concentrations of NH(g) and NH nor the concentrations of HNO(g) and NO at different pH levels. Higher concentrations of NO and NH were observed in the morning and evening, while no linear relationships were observed between the pH and concentrations of NH(g)-NH and HNO(g)-NO. The joint NH/HNO sensitivity regime map showed that most of the points were located in the HNO sensitive region with some in the NH & HNO sensitive region. In spring, autumn, and winter, most of the points were located in the HNO sensitive region while in summer, a significant quantity of the points were located in the NH & HNO sensitive region. Therefore, the precursors of HNO (such as NO) should be controlled in the spring, autumn, and winter, and attention should be given to the control of the precursors of HNO (NO) and NH in the summer to effectively control nitrate and ammonium aerosols in PM in Tianjin.
为研究细颗粒物（PM）中二次硝酸盐的形成及控制途径，基于2018年至2019年天津市中心城区某城市站点的高分辨率在线监测数据，对PM的离子组成、气溶胶pH值、NH₃ - NH₄⁺和HNO₃ - NO₃⁻浓度变化以及硝酸铵的联合NH₄⁺/HNO₃敏感性区域图进行了研究。结果表明，PM的平均浓度为58μg·m⁻³，PM的主要离子组成为硝酸盐（NO₃⁻）、铵盐（NH₄⁺）、硫酸盐（SO₄²⁻）、Cl⁻和K⁺，其相应质量百分比分别为18.4%、11.6%、10.3%、3.3%和2.6%。采暖季PM及其主要成分的浓度相对较高，非采暖季相对较低。气溶胶呈弱酸性，平均pH值为5.21；春季和冬季pH值较高，夏季和秋季较低，pH值的日变化在早晨（00:00 - 08:00）较低，其他时间略高。气态NH₃（NH₃(g)）和气态HNO₃（HNO₃(g)）的浓度分别为16.7μg·m⁻³和1.2μg·m⁻³。NH₃(g)的浓度在4月至9月相对较高，次年10月至2月相对较低。HNO₃(g)浓度没有明显的月度规律。除夏季外，NH₃(g)浓度在早晚较高，HNO₃(g)浓度在白天较高。在不同pH水平下，未观察到NH₃(g)与NH₄⁺浓度之间以及HNO₃(g)与NO₃⁻浓度之间存在明显的线性关系。早晚观察到较高浓度的NO₃⁻和NH₄⁺，而pH值与NH₃(g) - NH₄⁺和HNO₃(g) - NO₃⁻浓度之间未观察到线性关系。联合NH₄⁺/HNO₃敏感性区域图表明，大多数点位于HNO₃敏感区域，部分位于NH₄⁺ & HNO₃敏感区域。春季、秋季和冬季，大多数点位于HNO₃敏感区域，而夏季，大量点位于NH₄⁺ & HNO₃敏感区域。因此，春季、秋季和冬季应控制HNO₃（如NO₂）的前体，夏季应注意控制HNO₃（NO₂）和NH₃的前体，以有效控制天津市PM中的硝酸盐和铵盐气溶胶。
