| 天津市PM2.5中二次硝酸盐形成及防控 |
| 摘要点击 2458 全文点击 707 投稿时间：2020-10-19 修订日期：2020-11-30 |
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| 中文关键词 天津 二次硝酸盐 pH值 NH3 HNO3 敏感性图 |
| 英文关键词 Tianjin secondary nitrate pH value NH3 HNO3 sensitivity map |
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| 中文摘要 |
| 二次硝酸盐是PM2.5中的重要二次无机离子组分，为了解PM2.5中二次硝酸盐的形成及防控途径，基于天津市城区点位2018~2019年高时间分辨率的PM2.5在线监测数据，对气溶胶颗粒物的离子组分、pH值、NH3-NH4+和HNO3-NO3-浓度分布以及硝酸铵形成的敏感性进行了研究.结果表明，天津PM2.5平均浓度为58μg·m-3，PM2.5中主要离子组分为NO3-、NH4+、SO42-、Cl-和K+，在PM2.5中的占比分别为18.4%、11.6%、10.3%、3.3%和2.6%，PM2.5及主要组分浓度均在采暖季高、非采暖季低.气溶胶颗粒物整体呈现弱酸性，平均pH值为5.21，季节分布为春冬季节高、夏秋季节低，日变化趋势表现为早间（00：00~08：00）低，其他时间略高.NH3和HNO3的平均浓度水平分别为16.7μg·m-3和1.2μg·m-3，NH3浓度在每年的4~9月相对较高，10月~次年2月浓度相对较低；HNO3浓度水平月际变化不明显.除夏季外，其他季节NH3浓度均为早晚较高，其他时段较低；HNO3浓度整体呈现白天相对略高，晚上相对略低的特点.不同pH值下NH3与NH4+、HNO3与NO3-的浓度分布呈现明显的非线性关系，早晚NH4+与NO3-的浓度均较高，pH值与NH3和NH4+以及HNO3与NO3-的浓度分布均为非线性.敏感性图表明，2018~2019年天津市硝酸铵的形成主要处于HNO3敏感区域，部分处于NH3&HNO3敏感区域.从季节分布上看，春季、秋季和冬季硝酸铵的形成主要处于HNO3敏感区域，夏季硝酸铵的形成主要处于HNO3和NH3&HNO3敏感区域.为有效减少天津市PM2.5中二次硝酸盐的形成，春季、秋季和冬季主要开展HNO3前体物（NOx）的控制，夏季主要开展HNO3前体物（NOx）和NH3的协同控制. |
| 英文摘要 |
| To study the formation and approaches to controlling secondary nitrate in PM2.5, the ionic compositions of PM2.5, pH of aerosols, variations in NH3-NH4+ and HNO3-NO3- concentrations, and the joint NH3/HNO3 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 PM2.5 was 58μg·m-3, and the main ionic compositions of PM2.5 were nitrate (NO3-), ammonium (NH4+), sulfate (SO42-), Cl-, and K+ with corresponding mass percentages of 18.4%, 11.6%, 10.3%, 3.3%, and 2.6%, respectively. Concentrations of PM2.5 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 NH3(g) (gas NH3) and HNO3(g) (gas HNO3) were 16.7μg·m-3and 1.2μg·m-3, respectively. The concentrations of NH3(g) were relatively higher from April to September and lower from October to February of the following year. HNO3(g) concentrations did not show any clear monthly pattern. Except during the summer, NH3(g) concentrations were higher in the morning and evening, and HNO3(g) concentrations were higher during the day. No clear linear relationships were observed between the concentrations of NH3(g) and NH4+ nor the concentrations of HNO3(g) and NO3- at different pH levels. Higher concentrations of NO3- and NH4+ were observed in the morning and evening, while no linear relationships were observed between the pH and concentrations of NH3(g)-NH4+ and HNO3(g)-NO3-. The joint NH3/HNO3 sensitivity regime map showed that most of the points were located in the HNO3 sensitive region with some in the NH3 & HNO3 sensitive region. In spring, autumn, and winter, most of the points were located in the HNO3 sensitive region while in summer, a significant quantity of the points were located in the NH3 & HNO3 sensitive region. Therefore, the precursors of HNO3 (such as NOx) should be controlled in the spring, autumn, and winter, and attention should be given to the control of the precursors of HNO3 (NOx) and NH3 in the summer to effectively control nitrate and ammonium aerosols in PM2.5 in Tianjin. |
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