北京市区冬季颗粒态有机硝酸酯的污染特征与生成

有机硝酸酯是二次有机气溶胶的重要组分,对区域氮循环有重要意义。本次研究于2018年冬季在北京市区采集大气细颗粒物样品并测定5类主要有机硝酸酯的含量。结果显示,5类有机硝酸酯(包括单萜烯羟基硝酸酯、蒎烯羰基硝酸酯、柠檬烯羰基硝酸酯、油酸羰基硝酸酯和油酸羟基硝酸酯)的总浓度范围为127~528 ng/m^3,对二次有机气溶胶的平均贡献为5.6%,昼夜浓度基本相当。其中,单萜烯羟基硝酸酯的含量最高,平均占比高达41%。灰霾期间有机硝酸酯浓度明显升高,相关性分析表明,燃煤和机动车排放的NOx对有机硝酸酯浓度有显著促进作用。利用基于观测的盒子模型模拟了单萜烯羟基硝酸酯的生成速率,发现OH自由基和NO3自由基氧化分别是白天和夜间单萜烯羟基硝酸酯的主要生成途径,但模拟值普遍低于计算值,推测模型中的生成机制可能有一定缺失。结果表明,人为活动会影响有机硝酸酯的二次生成,削减NOx和臭氧有利于降低有机硝酸酯的大气浓度。

Pollution characteristics and formation of particulate organic nitrates in winter in Beijing City

Organic nitrates constitute a substantial fraction of secondary organic aerosols and have an important impact on reactive nitrogen budgets.In this study,samples of fine particulate matter were collected in urban Beijing in the winter of 2018 and the contents of five kinds of major organic nitrates were determined.The results show that the total concentration of the five kinds of organic nitrates ranged from 127 to 528 ng/m^3,including monoterpene hydroxyl nitrate,pinene keto nitrate,limonene di-keto nitrate,oleic acid keto nitrate,and oleic acid hydroxyl nitrate.On average,they contributed 5.6%to secondary organic aerosols.The average concentration during the daytime was comparable to that at nighttime.Among the five kinds of organic nitrates,the content of monoterpene hydroxyl nitrate was the highest,with an average contribution of up to 41%.During the haze period,the concentration of organic nitrates increased significantly.Correlation analysis showed that the concentration of organic nitrates was significantly influenced by NOx emitted from coal combustion and motor vehicles.An observation-based chemical box model was deployed to simulate the production rates of monoterpene hydroxyl nitrate.It was found that oxidation by OH radicals was the dominant formation pathway during the daytime,while oxidation by NO3 radicals was the major formation pathway at nighttime.Nevertheless,the simulated production rates of monoterpene hydroxyl nitrate were substantially lower than the calculated ones,which may be related to the deficiency of the reaction mechanism.This study indicates that anthropogenic activity could influence the secondary generation of organic nitrates.The reductions of nitrogen oxides and ozone are of great significance in decreasing the ambient concentration of organic nitrates.