海南省背景区域臭氧及其前体物污染特征

基于2019年五指山背景点、海口市和三亚市的环境空气自动监测数据和气象观测资料，分析了海南省背景区域和重点城市O₃及其前体物NO₂污染特征；结合挥发性有机物（VOCs）在线监测数据，分析了五指山背景点VOCs的时间变化规律、O₃浓度高值月份O₃及其前体物VOCs和NO_x的污染特征以及VOCs的臭氧生成潜势（OFP）.结果表明，O₃是影响五指山背景点空气质量的关键污染物，五指山背景点O₃日最大8 h浓度平均值与海口市和三亚市显著相关.背景点NO₂月均浓度水平显著低于城市点，然而背景点和城市点O₃月均浓度水平和变化趋势高度一致.背景点O₃变化与风向密切相关，春夏季偏南风频率较高，O₃浓度相对较低；秋冬季以东北风为主，易受内陆污染输送影响，O₃浓度较高.五指山背景点春夏季VOCs体积分数低于秋冬季，但对应的OFP高于秋冬季；其中异戊二烯夏季体积分数显著高于秋冬季，且其夏季体积分数占总挥发性有机物的比例最高，对应的OFP贡献率可达70%以上，O₃则表现出秋冬季显著高于夏季的特征.11月O₃高浓度时段乙炔和芳香烃的体积分数较清洁日出现较大上升，同时其对应的OFP显著上升.VOCs优势物种和OFP主要贡献物种的分析结果表明，O₃高浓度时段机动车尾气和油气挥发排放源对五指山背景点VOCs的化学组成和OFP有重要贡献.

Pollution Characteristics of Ozone and Its Precursors in Background Region of Hainan Province

Based on ozone and nitrogen dioxide (NO₂) automatic monitoring data and meteorological observation data of the Wuzhishan background site, Haikou, and Sanya in 2019, the pollution characteristics of ozone and its precursor NO₂ in the background region and key cities of Hainan Province were analyzed. Combined with volatile organic compounds (VOCs) online monitoring data, the time variation of VOCs, pollution characteristics of ozone and its precursors (VOCs and NO_x) during the month of high ozone concentrations, and the ozone formation potential (OFP) of VOCs at the Wuzhishan background site were investigated. The results showed that ozone was a key pollutant affecting the air quality of the Wuzhishan background site. The ozone daily maximum 8-hour average concentrations at the Wuzhishan background site were significantly correlated with Haikou and Sanya. The monthly average NO₂ concentrations at the background site were noticeably lower than those at the urban sites; however, the monthly average concentrations and change trends of ozone at the background site were highly consistent with those at the urban sites. Ozone concentration changes at the background site were closely related to the wind direction. The frequency of southerly winds was higher in spring and summer, and the concentration of ozone was relatively low. As the dominant wind direction changed to northeast in autumn and winter, the ozone concentration was relatively high due to the inland pollution transportation. The volume fractions of total volatile organic compounds at the Wuzhishan background site in spring and summer were lower than those in autumn and winter; however, the corresponding OFP saw an opposite tendency. The volume fraction of isoprene in summer was significantly higher than those in autumn and winter, and its volume fraction in summer accounted for the highest proportion of total volatile organic compounds, with the corresponding OFP concentration rate reaching over 70%, whereas ozone concentration showed the opposite trend. The volume fractions of acetylene and aromatic hydrocarbons during the periods of high ozone concentrations in November showed a major increase compared with those during the clean periods, and the corresponding OFP increased markedly. The analysis of the dominant species of VOCs and the main contributing species of OFP indicated that the emission sources of motor vehicle and gasoline or gas volatilization had a significant effect on the chemical composition and OFP of VOCs at the Wuzhishan background site during ozone high concentration periods.