Characteristics and causes of summer ozone pollution in Beijing City

Abstract

To investigate the characteristics and causes of ozone（O3）pollution in Beijing,continuous measurements of meteorological parameters,O3,nitrogen oxide（NOx）and carbon monoxide（CO）were conducted at an urban site in Beijing from July 15 to August 10,2017.In addition,offline one-hour whole air samples were collected on 7 selected days（i.e.20 and 30 July,and 1 and 4–7 August 2017）to analysis volatile organic compounds（VOCs）and oxygenated VOCs（OVOCs）.The results indicated that Beijing suffered from severe O3pollution,with the O3 episodes accounting for 51.8%of the whole sampling period.In general,high O3 days were associated with high temperature,low relative humidity,low pressure,and high levels of precursors（i.e.VOCs,CO and NOx）.On the VOCs sampling days,high O3 episodes were predominantly controlled by the Western Pacific Subtropical High or uniform pressure field（weak high pressure）.Furthermore,air masses from Hebei,middle Inner Mongolia and eastern Mongolia,passing by Baoding and Zhangjiakou,partially contributed to the observed O3 in Beijing.The average regional contribution to O3 accounted for 16%–37%,with a maximum of 53%The sensitivity analysis revealed that O3 formation in Beijing was mainly sensitive to VOCs,especially anthropogenic VOCs（AVOCs）.This study indicated that effective control of AVOCs emissions in Beijing and the surrounding cities may help to reduce O3 levels in Beijing. 为研究北京市夏季臭氧特征及污染成因, 于 2017 年 7 月 15 日至 2017 年 8 月 10 日期间, 在北京市城区进行气象要素、臭氧(O 3 ) 、氮氧化物(NOx)和一氧化碳(CO)的连续观测, 并选取 7 d(2017 年 7 月 20 日、30 日和 8 月 1 日、4~7 日)密集采集大气样品进行挥发性有机化合物(VOCs)和含氧挥发性有机化合物(OVOCs)的分析。结果表明, 观测期间北京市夏季 O 3 污染严重, 臭氧污染日以东南风为主, 一般伴随着高温、低湿、低压和高前体物(VOCs、CO 和 NOx)浓度, 占总观测天数的 51.8%。密集采样日中臭氧污染日的成因与副热带高压或均压场下的弱高压系统有关。此外, 来自河北、内蒙古中部和蒙古国东部途经保定和张家口等地的气流为北京夏季臭氧污染日的形成提供了部分外源, 日平均贡献量为 16%~37%, 最大贡献量为 53%, 显示区域传输对臭氧污染日形成有重要影响。敏感性试验发现 O 3 的生成主要受 VOCs 控制, 特别是人为源 VOCs。以上结果表明, 控制北京本地 VOCs 的人为排放和周边空气质量将有助于降低北京城区的 O 3 浓度。