国庆期间南岭背景大气中PAN的浓度特征与来源

为了评估华南地区国庆期间频发的大范围区域光化学污染事件对华南背景大气的影响，2018年国庆节前后（9月19日~10月19日），在广东南岭国家大气背景站对光化学污染的代表产物过氧乙酰硝酸酯（PAN）开展了连续在线观测，并对PAN的浓度特征和来源进行了分析.结果表明，研究期间南岭PAN的平均体积浓度为（0.66±0.54）×10^-9，最大值为2.33×10^-9，显著高于国内外其他背景站点（（0.21~0.44）×10^-9），且PAN的夜间浓度一直维持在较高的水平；PAN和O₃（r=0.90）、NO₂（r=0.87）的相关性较强，通过PAN和O₃的线性拟合估算出O₃的大气背景体积浓度为（46.22±0.65）×10^-9，表明南岭光化学反应十分活跃；受区域光化学污染事件的影响，国庆期间南岭PAN的浓度显著升高，达到（1.18±0.45）×10^-9，而同期NO/NO₂比值降低，导致PAN大气寿命延长，有利于PAN的本地累积；结合气团后向轨迹，潜在源贡献分布以及前体物NO₂的全国分布特征分析，发现国庆期间高浓度PAN主要来自湖南，湖北、河南、江西等华中地区.

Concentration characteristics and sources of PAN at Nanling background station during the National Day holidays

To evaluate the influence of the frequent large-scale regional photochemical pollution events on the background atmosphere in South China during the National Day holiday, continuous online observations of peroxyacetyl nitrate (PAN) a representative product of photochemical pollution, were conducted for the first time at Nanling National Atmospheric Background Monitoring Station in Guangdong, around the National Day of 2018 (September 19^th~October 19^th). The concentration characteristics and sources of PAN were also analysed. The average volume concentration of PAN during the period was (0.66 ±0.54)×10^-9, with the maximum value of 2.33×10^-9, which was significantly higher than other background sites in China and abroad ((0.21 ~ 0.44)×10^-9), and the concentration at night was constantly high. Additionally, PAN correlated well with O₃ (r= 0.90) and NO₂ (r = 0.87), and the atmospheric background volume concentration of O₃ was estimated to be (46.22 ±0.65)×10^-9by a linear fitting method, indicating that the photochemical reaction at Nanling was active. As a result of the regional photochemical pollution events, the concentrations of PAN at Nanling site increased significantly during the National Day holiday, reaching (1.18 ±0.45)×10^-9,while NO/NO₂ ratio decreased during the same period, resulting in a prolonged atmospheric lifetime of PAN and contributing to local accumulation of PAN. Combining the backward trajectory of the air mass, the distribution of potential sources and the nationwide distribution characteristics of the precursor NO₂, it was found that the high concentration of PAN during the National Day holiday at Nanling site mainly came from Hunan, Hubei, Henan, Jiangxi and other central regions of China.