雅安市春季一次典型臭氧污染过程分析

Analysis of a typical springtime ozone pollution process in Ya'an

雅安市春季(4—5月)臭氧(O_(3))污染问题日渐凸显.基于雅安市区国控监测站点大气O_(3)监测数据,运用HYSPLIT后向轨迹模式、潜在源贡献因子法(WPSCF)与浓度权重轨迹分析(WCWT)等方法,探讨了2015—2023年雅安市春季O_(3)污染特征及一次典型O_(3)污染过程(2023年4月9—10日)成因.结果表明,春季雅安MDA8 O_(3)浓度和O_(3)超标天数波动上升,2023年分别达到111μg·m^(-3)和9d,活跃的本地光化学生成过程和区域传输过程是重要驱动因素.在春季O_(3)污染的形成过程中,低水平风速、盆地内下沉气流作用等不利的扩散条件使得雅安市区各类污染物累积、浓度水平显著升高,特别是夜间O_(3)浓度升高导致较高的本底浓度水平.日间700 hPa以下高度上24 h增温显著、较强的太阳辐射和低湿条件,有利于NO_(x)和VOCs等前体物快速发生光化学氧化反应形成O_(3).潜在源区(眉山和成都等)O_(3)及其前体物的传输,加剧了雅安市午后O_(3)污染程度,O_(3)浓度增长可达20μg·m^(-3)以上.因此,对雅安市春季O_(3)污染的防控需要加强本地前体物减排,同时考虑对周边地区施行协同减排措施.

Ozone(O_(3))pollution in spring(from April to May)has drawn increasing attention in Ya'an.This study explored the characteristics of O_(3) pollution(Spring 2015—2023)and the causes of a typical springtime O_(3) event in Ya'an(Apr 9—10,2023)based on the O_(3) measurements at the national air quality monitoring sites,the HYSPLIT backward trajectory model,the weighted potential source contribution factor(WPSCF)and the weighted concentration-weighted trajectory(WCWT).The results showed that springtime MDA8 O_(3) concentration and O_(3) polluted days in Ya'an exhibited fluctuating ascending trends,reaching 111μg·m^(-3) and 9 d in 2023,respectively.Active local photochemical production and regional transport were key drivers.During the springtime O_(3) pollution process,unfavorable diffusion conditions(e.g.,low wind speed and subsidence flow from the Sichuan basin)led to the accumulation of various pollutants in Ya'an urban area.Especially,the nighttime O_(3) concentrations significantly increased,indicating the rise of background O_(3) levels.In the daytime,an obvious increasing temperature in the Sichuan Basin below 700 hPa height,intense solar radiation,and low relative humidity promoted the rapid photochemical production of O_(3) from its precursors(i.e.,NO_(x) and VOCs).In the afternoon,the transport of O_(3) and its precursors from the potential source regions(including Meishan and Chengdu)further aggravated O_(3) pollution in Ya'an,with an increase in O_(3) concentration of more than 20μg·m^(-3).The joint efforts to reduce pollutant emissions in Ya'an and its upwind regions are essential to effectively mitigate springtime O_(3) pollution.