华北典型地区PM2.5有机硝酸盐污染特征及其生成转化研究

Organic nitrates are among the main components of atmospheric fine particles and in particular secondary organic aerosols (SOA). They play important roles in atmospheric chemical processes such like removal of NOx via chemical transformation and degradation of VOCs by oxidation. Recent international studies suggest that the production of organic nitrates through VOCs oxidation by NO3 radicals in night-time significantly contributes to SOA formation. Organic nitrates were also found to absorb short-wave solar radiation strongly and thus could apparently alter the solar radiative forcing. Due to lack of measurements of organic nitrates in real atmosphere and lack of studies on related chemical processes, knowledge gaps remain on the pollution characteristics and formation mechanism in polluted atmospheric environment in North China region. In the present project, we plan to collect PM2.5 samples in typical areas in North China and detect the contents of major organic nitrates. In the same time, related atmospheric pollutants and meteorological parameters will be monitored. We will then analyze the chemical composition, concentration levels, and temporal and spatial variation laws of the PM2.5 organic nitrates. The formation mechanism, contribution to SOA, and optical characteristics of organic nitrates will also be explored. This study will enrich the knowledge on the hot scientific problem on organic nitrates. The research results can be applied in the deep evaluation the optical and health effects of PM2.5. They can also provide scientific supports for SOA and PM2.5 control in local areas.

有机硝酸盐是大气细粒子尤其是二次有机气溶胶（SOA）的重要成分之一，在NOx转化去除与VOCs氧化降解等大气化学过程中起重要作用。国际上最新研究表明，NO3自由基氧化VOCs形成有机硝酸盐对夜间SOA生成有重要贡献；有机硝酸盐对短波太阳辐射有强烈吸收，会显著改变太阳辐射强迫。由于缺少对实际大气细颗粒物中有机硝酸盐的测定及相关化学过程的研究，我国华北地区污染大气环境下有机硝酸盐的污染特征及生成机制尚不清楚。本项目拟在华北典型地区采集PM2.5样品并检测主要有机硝酸盐的含量，同时对相关污染物及气象参数进行测量，分析PM2.5有机硝酸盐的化学组成、浓度水平与时空变化规律，探讨典型天气条件下有机硝酸盐的生成机制、SOA贡献率、光学特性等。本研究将大大丰富目前关于有机硝酸盐这一热点科学问题的认识，研究成果可应用于PM2.5光学与健康效应的深入评估，也可为当地SOA及PM2.5控制提供科学支撑。

有机硝化物和硝酸酯是大气细颗粒物的重要成分之一，影响环境空气质量和区域气候，在NOx转化和VOCs氧化等大气化学过程中起重要作用。然而由于缺少实际大气细颗粒物中含氮有机物的测定及相关过程分析，我国华北污染大气环境下有机硝化物和硝酸酯类化合物的污染特征与生成机制尚不清楚。本项目对大气硝基酚类化合物的测定方法进行优化，基于HPLC-MS识别并定量大气颗粒物中5类有机硝酸酯。在华北典型城市、乡村和高山站采集大气PM2.5样品，检测主要硝基酚类化合物的含量，同时对相关含氮化合物等进行测量，发现华北地区细颗粒物中硝基酚类化合物的浓度水平与化学组成呈现明显的时空差异，城市冬季浓度最高，主要来自于交通源、生物质燃烧、燃煤源、老化的燃煤气团和二次生成，夏季显著的二次生成主要受硝化过程控制；济南冬季NO2的非均相转化不仅生成HONO，还生成大量亚硝酸盐，亚硝酸盐在白天干燥、酸性气溶胶条件下可释放HONO；济南夏季N2O5的浓度高值与燃煤烟羽有关，其非均相反应促进了无机硝酸盐的大量生成，同时产生较高浓度的ClNO2，但ClNO2产率很低，很可能与含氯气溶胶和其他不溶性物质内部混合有关。另外开展了实验室模拟燃烧实验，获得华北地区常见生物质燃烧产生的细粒子硝基酚类化合物的排放特征和排放系数，排放因子为0.75-11.1mg/kg，2014年玉米芯、玉米秆和小麦秆燃烧的排放量约为670吨。本项目关于华北PM2.5硝基酚类化合物及相关含氮化合物污染特征、来源和转化的研究，为未来进一步研究硝基酚类化合物的一次排放量、二次生成途径和气候效应提供了重要的基础数据和理论依据。