气象条件对天津冬季低层大气中PAN浓度的影响

采用在线仪器监测分析2017年冬季天津气象铁塔220m观测平台大气中过氧乙酰硝酸酯（PAN）的体积浓度，并结合污染物资料、气象观测资料和后向轨迹分析造成PAN高值的影响因素.观测期间天津城区大气中PAN的体积浓度平均值为（0.57±0.54）×10^-9，PAN体积浓度存在2个峰值，大体上对应着2次重污染过程.PAN与O₃间不存在明显的相关性，但与PM_2.5质量浓度相关性较好，表明光化学反应并非影响冬季PAN浓度的唯一因素，后向轨迹的聚类分析以及改进的静稳指数显示远距离输送和本地积累对PAN浓度的时空分布发挥了较大作用.对观测期间一次重污染天气过程中温度、相对湿度和风的垂直廓线，以及混合层厚度等气象条件的分析表明，PAN浓度上升既受到区域输送影响，也与静稳天气下的污染物积累有关.

Influence of meteorological conditions on PAN concentration in the lower boundary layer atmosphere of Tianjin in winter

The volume concentration of peroxyacetyl nitrate (PAN) in the atmosphere was measured at the Tianjin meteorological tower in the winter of 2017 by using the on-line instrument along with meteorological parameters and the back trajectory analysis to analyze the formation of high concentration PAN. The average volume concentration of PAN during the observational period was (0.57±0.54)×10^-9 with two peaks, accompanied by two heavy pollution processes. The correlation coefficient between PAN and O₃ was obviously lower than that between PAN and PM_2.5, indicating that photochemical reaction may not be the main influencing factor of PAN concentration in winter.The clustering analysis of backward trajectory and stable weather index (SWI) indicated that long-distance transportation and local accumulation may play a more important role. The rise of PAN concentration was affected by the long-range transport of the wind to the south. It also has something to do with quiet and stable weather. The meteorological conditions such as vertical profiles of temperature, relative humidity and wind, and thickness of mixing layer during a heavy polluted weather were analyzed. The results showed that increased PAN concentration was dominantly contributed by both regional transport from surrounding areas and the accumulation of pollutants in stationary weather.