基于激光雷达观测的青岛市暖季臭氧污染垂直分布特征

Vertical Distribution Characteristics of Warm Season Ozone Pollution in Qingdao Based on Lidar Observations

为探究暖季臭氧(O_(3))污染垂直分布特征及其影响因素,利用差分吸收臭氧激光雷达和相干多普勒测风激光雷达等对青岛市沿海地区2023年6−9月大气边界层2000 m以内O_(3)浓度和边界层风场开展长期连续观测,并基于O_(3)输送通量垂直分布揭示可能的污染来源。结果表明:①观测期间共发生O_(3)污染日24 d,O_(3)-8 h浓度(O_(3)日最大8 h平均浓度)平均值为(183±24)μg/m^(3);清洁日共98 d,O_(3)-8 h浓度平均值为(118±30)μg/m^(3)。O_(3)污染过程多与升温过程密切相关,在较强太阳辐射和低相对湿度条件下更容易发生O_(3)污染。②垂直方向上O_(3)主要分布在1000 m以下。清洁日各高度层日间和夜间O_(3)浓度变幅较小,污染日各高度层O_(3)浓度单峰型日变化特征显著,且日变化特征随高度升高而逐渐减弱。清洁日日间、夜间以及污染日夜间O_(3)浓度垂直廓线均存在峰值,峰值浓度分别为(115±3)(112±2)和(130±3)μg/m^(3),峰值高度范围为400~650 m,可能与近地面NO滴定效应等消耗O_(3)有关,也可能是残留层储存的日间高浓度O_(3)或残留层O_(3)水平输送导致,但污染日日间垂直廓线呈随高度上升而O_(3)浓度逐步下降的特征,表明近地面前体物光化学生成是O_(3)污染的主要来源。③当西北风和西南风更替、低空暖平流和较强下沉气流等大气条件发生时,有利于污染物累积和O_(3)生成,从而引发O_(3)污染。清洁日低空(近地面至600 m高度)受较为清洁的海洋气流影响,污染日受内陆方向气流影响。④污染日凌晨至上午受来自偏西、西南或西北上风向O_(3)水平输送影响,高空O_(3)伴随下沉气流向下混合,与本地排放前体物在日间高温、强太阳辐射等气象条件下生成的O_(3)叠加,从而加剧地面O_(3)污染,午后高浓度O_(3)在较高水平风速影响下也可能向下风向地区输送。研究显示,O_(3)污染防治不仅要做好本地前体物的精准管控,还要加强区域联防联控,从而实现空气质量持续改善。

In order to explore the vertical distribution characteristics of warm season ozone pollution and its influencing factors,comprehensive long-term observations were conducted on ozone mass concentration and wind profiles within the atmospheric boundary layer up to 2000 m above the coastal area of Qingdao from June to September 2023,by using differential absorption ozone lidar and coherent Doppler wind lidar.Possible pollution sources were revealed based on the vertical distribution of ozone transport flux.The research results show that:(1)The observation identified 24 pollution days and 98 clean days,with average O_(3)-8 h(daily maximum 8 h moving average of ozone mass concentration)of(183±24)and(118±30)μg/m^(3),respectively.The ozone pollution processes were closely related to rising temperatures and were more likely to occur under conditions of intense solar radiation and lower relative humidity.(2)The vertical distribution of ozone was predominantly distributed below 1000 m.On clean days,ozone mass concentration was relatively uniform,with minimal fluctuations in both daytime and nighttime at different altitudes.However,on pollution days,ozone mass concentration showed a unimodal diurnal variation at different altitudes,and the diurnal variation characteristics weakened as height increased.The vertical profiles of ozone mass concentration showed peaks during both daytime and nighttime on clean days,and during nighttime on pollution days.The peak concentrations were(115±3),(112±2)and(130±3)μg/m^(3),respectively.These layered peaks were observed in the height range of 400 m to 650 m,and could be attributed to near-surface NO titration effects or the daytime high concentrations of ozone stored in the residual layer.However,the daytime ozone mass concentration profiles indicated a gradual decrease with increasing height on pollution days,suggesting that near-surface photochemical production was the primary source of ozone pollution.(3)Atmospheric conditions such as alternating northwest to southwest winds,low-level warm advection,and strong subsidence airflow were conducive to ozone and its precursors accumulation and ozone formation,leading to ozone pollution.On clean days,the lower atmosphere(from near the surface to 600 m)was predominantly influenced by clean maritime airflow,while on pollution days,it was originated from inland airflows.(4)From the early morning to the morning on the pollution days,ozone was transported from upwind areas in the west,southwest,or northwest.Ozone from higher altitudes was then mixed downward to the surface by downdrafts,where it combined with ozone generated by local precursors under meteorological conditions of high air temperatures and intense solar radiation,thereby exacerbating ozone pollution.Subsequently,the strong wind facilitated the transport of these elevated ozone to downwind areas in the afternoon.This study suggested that the prevention and control of ozone pollution should not only focus on precise control of local precursors,but also strengthen regional collaborative efforts to achieve continuous improvement of air quality.