大气灰霾期硝基多环芳烃的粒径分布与生成机制研究

Nitro-polycyclic aromatic hydrocarbons (NPAHs) are important organic pollutants during haze process and have strong potential human health risks. At present, the atmosphere environment in China shows new features with increasing of atmosphere oxidation, particulate matter levels, and proportion of nitrogen components in particular, which will seriously affect the particle size distribution of NPAHs and their migration and transformation. In this study, we will take the atmospheric NAPHs in different seasonal haze periods in Beijing-Tianjin-Hebei regions as the research object. We will mainly collect seasonal dynamic samples of gas and particulate matter with different particle size. The composition and concentration of polycyclic aromatic hydrocarbons and NPAHs will be measured. The methods of positive matrix factorization model (PMF) and ratio method will be used to identify the sources. On-line observation of conventional polluted gases and meteorological parameters will be carried out, which will measure the concentration of SO2、NOx、O3、VOCs and temperature, humidity, solar radiation etc. Taking the main polluted species as the target, we will select the quantum chemical theoretical calculation to analyze the optimal reaction path and verify the field observation results. Combined the samples of gas and particulate matter with conventional polluted gases and meteorological parameters, we will elucidate the characteristics of particle size distribution of NPAHs and its main sources during the haze period in Beijing-Tianjin-Hebei region. We will also elucidate the optimal reaction path and generative mechanism of NPAHs. This study will provide scientific cognition and data support on the migration and transformation of NPAHs and the risk assessment of human health.

硝基多环芳烃(NPAHs)是灰霾过程中一类重要有机污染物，具有较强的潜在人体健康风险。当前我国大气氧化性不断增强、颗粒物浓度和含氮组分占比逐渐增高，这可能显著影响NPAHs的粒径分布及迁移转化。拟以京津冀区域灰霾期大气中NPAHs为研究对象，采集气态和不同粒径颗粒物的季节动态样品，测定多环芳烃和NPAHs组分和浓度等指标，利用正交矩阵因子分解法和比值法等进行来源识别；配套开展常规污染气体和气象参数的在线观测，测定SO2、NOx、O3等指标；以观测结果中PAHs优势物种为目标物，采用量子化学计算方法，解析其最佳反应路径，并对外场观测结果进行验证。将气态和颗粒物样品与常规污染气体和气象参数相结合，综合揭示京津冀区域灰霾期NPAHs的粒径分布特征及主要来源；通过量子化学计算，进一步阐明NPAHs的最佳反应路径，为深刻理解大气中NPAHs的迁移转化规律及人体健康风险评价提供科学认识和数据支撑。

当前我国大气环境呈现新的特征，大气氧化性不断增强，大气颗粒物中含氮组分的占比显现出逐渐增高的趋势，这将严重影响大气硝基多环芳烃的迁移转化。目前国内外对多环芳烃的相关研究较多，但是对其衍生物特别是硝基多环芳烃的粒径分布特征、二次生成机制尚缺乏系统研究。本研究通过采集北京典型城区PM2.5样品和分粒径样品，重点分析了其中的16种多环芳烃和17种硝基多环芳烃，探讨了它们的浓度水平、粒径分布、来源等的季节变化特征，结合量子化学计算，阐明了NPAHs的最佳反应路径，验证了外场观测的结论，同时开展了环境风险评估。项目观测结果表明，PAHs和NPAHs浓度呈现明显的季节变化特征，表现为冬季浓度最高，夏季浓度最低；PAHs和NPAHs有明显的日变化特征，夜间浓度是白天浓度的2-3倍；NPAHs主要分布在超细颗粒上（空气动力学直径<1.1微米）；利用皮尔逊相关性分析和比值法得出的PAHs和NPAHs来源结果表明，机动车排放（特别是柴油车尾气）在四个季节都是重要来源，生物质燃烧和燃煤在秋冬季时贡献较为突出，夏季时二次非均相反应明显影响NPAHs的生成；PAHs转化生成NPAHs的影响因素分析结果显示，过量的NO2会促进二次组分从无机向有机转变，一定范围内的湿度（<60%）有利于气相有机物和液相反应向颗粒相中分配，NO3-/NPAHs比值在60%-80%湿度范围内达到最高，表明更高的湿度更促进无机硝酸盐的生成；量子理论计算结果在一定程度上解释了为什么在高NO2地区外场观测到的2N+3N-FLA主要以2N-FLA为主；健康风险评估结果显示青少年群体有最高的潜在癌症风险。近年来北京市PM2.5浓度明显下降，但由PAHs和NPAHs暴露而引起的对人体健康的潜在风险不容忽视，未来仍需进一步加强控制大气污染。本项目研究成果有利于进一步认识大气中硝基多环芳烃的迁移转化规律及来源特征，为该类污染物的减排和控制，以及降低人体健康风险提供有力的科学依据。