南宁秋季典型光化学污染过程HONO特征及来源研究

On nitrous acid features and its source of a typical photochemical pollution episode in autumn in Nanning,Guangxi

HONO是·OH重要前驱体,在大气化学反应中起着关键作用。为了解光化学污染期间HONO的特征及来源,采用离子色谱法测量南宁市典型光化学污染期间大气中HONO的质量浓度,同时测量硝酸(HNO3)、颗粒物(PM)、氮氧化物(NOx)、一氧化碳(CO)和臭氧(O3)质量浓度。结果表明,高温、低湿度和低风速等不利气象条件是产生污染的重要诱因;HONO污染期间质量浓度平均值为3.09μg/m^3,是非污染期间的1.6倍;机动车直接排放对HONO的平均贡献率为18.9%;NO和·OH反应生成HONO的净速率平均值为0.89μg/(m^3·h);无论昼间或夜间,NO2对转换成HONO非均相反应均会产生影响,夜间HONO平均转化率为1.09×10^-2h^-1。相关性分析表明,大气颗粒物硝酸盐非均相反应可能是HONO的来源之一。

In order to identify and clarify the characteristic features of HONO in the urban area,this paper tries to measure the concentration density of the atmospheric HONO during the seasons of the typical photochemical pollution in Nanning,the capital city of Guangxi Autonomous Region.As a matter of fact,nitric acid(HNO3),the particulate matter(PM),the nitrogen oxides(NOx),the carbon monoxide(CO)and Ozone(O3)concentration come along to constitute an important precursor of OH radicals.It plays a dominant role in the atmospheric chemical reaction through the ion chromatography.Though it is possible to determine the concentration rate of HONO in the atmosphere of the urban areas,it remains limited for the atmospheric science area to master and control the basic knowledge of its characteristics and sources for the time being.Therefore,the given paper tries to analyze the information and data concerned to elucidate the basic features of HONO,their emissions,the homogeneous gas-phase and the heterogeneous reactions.And then,the research steps can be divided into the period of pollution or contamination and that of clarification by using the O3 concentration.The average concentration rate of HONO in the polluting period can be 1.6 times of that of the period of cleaning up.And,then,the results of cleaning up tend to reveal a typical diurnal variation pattern of low concentration during the daytime but high concentration at night each day.When compared with the state of concentration originally collected from another city,the vehicular emissions have been found in estimation at a contribution rate of 18.9%of the HONO concentrations at night,with its highest contribution rate being 21.1%at 20:00.What is more,a well in accord correlation can be found between HONO and PM2.5,and between HONO and HNO3.In addition,the average net rate of HONO formation from NO and OH reaction has been found equal to 0.89μg/(m^3·h).And,the average heterogeneous conversion rate of NO2-to-HONO during the pollution periods can be found equal to 1.09×10^-2h^-1.The results of our comparison prove that the conversion of NO2-to-HONO should have an obvious effect on the formation of HONO for the daytime as well as for the night hours,which may imply that the nitrates of atmospheric particulates may come from the same source of HONO.Thus,it can be concluded that the given study should be in a position to improve the comprehensive understanding of the HONO sources and the atmospheric chemistry in a polluted urban area.