2017年秋季海口市一次持续空气污染过程特征及成因分析

Characteristics and source analysis of a multi-day air pollution episode in Haikou City in autumn 2017

2017年秋季海口市发生了一次罕见的持续空气污染过程.本文基于AQI和6类大气污染物浓度资料、气象观测资料、和ERA-interim再分析资料等,结合后向轨迹模式(HYSPLIT)进行深入分析.结果表明,臭氧(O_(3))是此次污染事件的主要污染物,污染时段AQI和O_(3)浓度平均值分别为114μg·m^(-3)和175.3μg·m^(-3).污染时段没有降水,气温和日照时数稳定,相对湿度偏低(68.4%),平均风速超过3.7 m·s^(-1),这种气象条件有利于外源污染输送和污染物浓度的维持.此次空气污染的发生与天气形势演变关系密切,低层稳定的东北风场为外源输送提供了持续的动力条件,较小的相对湿度和地表大于6℃的温度露点差为光化学烟雾的发生提供了有利条件.后向轨迹分析结果表明,不同层次上的气流轨迹运动方向基本一致,速度略有不同,同时影响气流在传输的过程中均伴有下沉和加压,限制了污染物的垂直扩散,对海口市此次O_(3)污染的发展和维持有直接作用.潜在源区分析表明,广东是此次O_(3)污染过程的主要贡献源区,其WPSCF值和WCWT值分别在0.21和40以上.此外湖南东南部、江西西部、江苏南部、浙江南部、福建中南部地区也有一定的潜在贡献.

This study investigated an uncommon long-duration(13 days) air pollution episode that occurred in Haikou City during autumn 2017, with the use of multiple metrics, including AQI value and concentrations of 6 atmospheric pollutants, meteorological data ERA-interim reanalysis data and HYSPLIT backward trajectory model. The results indicated that ozone(O_(3)) was the main pollutant in this episode, and the average AQI and O_(3) concentrations were 114 and 175.3 μg·m^(-3), respectively. The meteorological conditions, such as no raining, stable temperature and sunshine duration, low relative humidity(68.4%) and daily average wind(exceeded 3.7 m·s^(-1)) were all favorable with this exogenous pollution and maintenance of O_(3) concentration. In addition, development and maintenance of this air pollution episode was closely related to the evolution of weather situation. The stable lower-tropospheric northeastly wind provided continuous dynamic conditions for external transportation. Otherwise, the low humidity and more than 6 ℃ difference between surface air and dew point temperature provided favorable conditions for the photochemical smog. Our further analyze on the backward trajectory show that direction and speed of the airflow in different levels were different. The airflow in the process of transmission is accompanied by sinking and pressurization, which limited the vertical diffusion of air pollutants, resulting in the development and maintenance of this air pollution episode. For the potential source, Guangdong is the main potential contribution region for this pollution episode, where the associated WPSCF and WCWT were above 0.21 and 40, respectively. Besides, southeastern Hunan, western Jiangxi, southern Jiangsu, southern Zhejiang, and central and southern Fujian also have some potential contributions for this episode.