2013年夏季嘉兴市一次光化学事件的观测分析

Observation of a Photochemical Event in Jiaxing During Summer 2013

为研究2013年8月5~11日嘉兴地区一次光化学事件形成的高浓度O3污染的变化特征及成因,对8月2~14日的主要污染气体(O3、NO2、NO、CO、SO2)、颗粒物(PM10、PM2.5)以及气象要素进行了观测分析.结果表明,嘉兴污染日的O3平均浓度是正常日的2.4倍,超标率多在29.0%以上,9日超标率高达45.8%,此次污染事件是高温下剧烈的光化学反应以及低湿低风速的稳定天气形势共同作用造成的.污染日和正常日的O3日变化均呈单峰分布,峰值出现在14:00左右,O3在污染日和正常日生成期的增长速率分别为50.3μg·(m3·h)-1和21.6μg·(m3·h)-1,在消耗期的下降速率分别为16.8μg·(m3·h)-1和23.4μg·(m3·h)-1,NO、NO2和CO在污染日的浓度分别是正常日的1.1、1.5和1.5倍,为光化学反应提供了有利的反应条件.污染日PM2.5浓度、PM10浓度、PM2.5/PM10的比值分别是正常日的2.5、2.3、1.1倍,污染日大气光化学反应异常活跃,更有利于细颗粒物的生成.

To investigate the variation characteristics and causes of a high-level ozone pollution event during Aug. 5-11,2013 in Jiaxing,the pollution gases( O3,NO2,NO,CO,SO2),atmospheric particles( PM10,PM2. 5),and meteorological elements were observed in this study. The results indicated that the O3concentration on the pollution days was 2. 4 times higher than that on normal days,with an exceeding rate of over 29. 0% and up to 45. 8% on Aug. 9. This event was induced by the combined influences of intensive photochemical reaction at high temperature and in static stability weather condition with low humidity and wind speed. The diurnal variation of O3showed a unimodal distribution on pollution and normal days,with the highest value at around 14: 00. In the generation stage,the growth rates of O3were 50. 3 and 21. 6 μg·( m3·h)- 1on pollution and normal days,respectively; in the extinction stage,the decrease rates of O3were 16. 8 and 23. 4 μg·( m3·h)- 1. The concentrations of NO,NO2and CO on pollution days were 1. 1,1. 5,and 1. 5 times higher than those on normal days,which provided favorable conditions for photochemical reaction. The concentrations of PM2. 5,PM10,and the ratio of PM2. 5/ PM10on pollution days were 2. 5,2. 3,and 1. 1 times higher than those on normal days,indicating that the photochemical reaction is more conducive to the formation of fine particles.