城市干道附近大气活性氮污染时空分布特征及其来源识别

Reactive nitrogen (Nr) emissions from road traffic can create corridors of increased atmospheric Nr concentrations and subsequent high nitrogen deposition fluxes near roads, and thus can lead to various eco-environmental problems. It is essential to reveal the characteristics of atmospheric Nr pollution near roads to protect human health and eco-environmental security. Therefore, this project will carry out a case study near a typical urban arterial road in Shenyang City. Samples of atmospheric NOx, NO2, HNO3 and NH3 will be collected monthly by passive samplers at different distances from the road and at different heights. Compared to the atmospheric wet deposition of nitrogen, the characteristics of the spatio-temporal distributions of atmospheric NOx, NO2, HNO3 and NH3 concentrations and their deposition fluxes will be revealed. And then the contributions of different sources to these atmospheric Nr species will be evaluated using 15N tracing technique. The following scientific questions will be studied. What are the patterns of the spatio-temporal distributions of atmospheric NOx, NO2, HNO3 and NH3 concentrations and their deposition fluxes near the arterial road, and what are the differences among different Nr species? What are the contribution ratios as well as their spatio-temporal variations of different sources of atmospheric NOx, NO2, HNO3 and NH3 near the arterial road? This project will not only provide basis for further improvement of exhaust emission standard for on-road vehicles and better protection and remediation of atmospheric Nr pollution and negative eco-environmental effects caused by excess nitrogen deposition, but also provide basic data for accurate estimation of nitrogen deposition fluxes in areas with dense networks of traffic.

道路交通活性氮排放使道路两侧局部区域成为大气活性氮污染物富集带和高通量氮沉降带，进而引发各种生态环境问题。在交通干道附近开展大气活性氮污染的研究对于保护人体健康和生态环境安全来说意义重大。本项目以沈阳市典型交通干道为例，采用被动取样法系统采集干道附近不同距离、不同高度大气NOx、NO2、HNO3和NH3样品，以研究区大气氮湿沉降作为对照，揭示它们的浓度及沉降量的时空分布特征，并结合15N溯源的方法识别不同污染源对大气活性氮污染的贡献。拟解决的关键科学问题包括：1）交通干道附近大气NOx、NO2、HNO3和NH3浓度和沉降通量的时空分布规律及不同污染物间的差异是什么？ 2）不同污染源对大气活性氮污染的贡献及其时空分布规律是什么？本项目的开展预期能够为进一步完善机动车尾气排放标准、防治大气氮污染和过量氮沉降引发生态环境负效应提供依据，并为准确估算交通密集区域氮沉降通量积累基础数据。

道路交通排放的NOx（NO+NO2）使道路两侧区域成为大气NO2污染富集带，易引发各种生态环境问题。在交通干道附近开展大气NO2污染特征的研究对于保护人体健康和生态环境安全来说意义重大。本次工作以沈阳市道义南大街沈阳师范大学毗邻路段为研究对象，用自制Willems型被动取样器在距干道0.5、3.34、9.49、23.17、36.75、96.44和455 m（该点位于6楼顶）处采集大气NO2样品，采样频率为1次/2周，部分样品1次/4周，测试污染物捕集量及其15N组成，分析大气NO2浓度及其15N组成时空分布特征。同时在两个环境监测站验证取样器实际采样速率和主要影响因素，采样频率为1次/1周、1次/2周和1次/4周。结果表明，相对湿度是影响研究区取样器NO2采样速率的关键因子。当大气NO2浓度较高时，可通过缩短取样时长或增加吸收介质层数（厚度）来降低被动法测量误差。大气NO2浓度空间分布和15N溯源技术证实，冬季大气对流作用较弱时，易引起交通干道附近NO2浓度急剧升高，随距离增加近似呈指数衰减。春、夏季大气对流作用较强时，大气NO2浓度最大值不一定出现在紧邻干道位置，而且污染源的影响距离也增大，即临近干道大气NO2浓度随距路缘距离增加迅速衰减，超过一定距离后则缓慢衰减。交通源对路旁大气NO2污染的贡献可超过该处浓度与背景浓度的差值，偏差可达6.52～6.89 μg/m3。研究区交通源排放NO2 δ15N值变化范围为11.3～36.8‰，平均19.1‰。总体上，干道附近大气NO2污染较为严重，应采取更为严格的交通源控制措施。