2016—2020年西安市近地面臭氧污染变化趋势及分布特征

Trends and Distribution of Ground-Level Ozone Pollution in Xi’an City During 2016-2020

利用2016—2020年陕西省环境空气质量自动站的臭氧监测数据,分析西安市大气环境中臭氧污染的时间变化趋势及空间分布特征。从时间分布来看,西安市臭氧年均质量浓度呈先上升后下降的波动变化趋势,且浓度值略高于全国平均水平;臭氧月均浓度具有明显的季节变化特征,月超标天数和月均质量浓度均在6月达到峰值;臭氧质量浓度日变化规律在全年和四季完全一致,均呈单峰型,日内小时平均质量浓度超标最多时段集中在15:00—16:00;臭氧与NO_(2)、CO均呈“此消彼长”的负相关关系。从空间分布来看,西安市12个国控评价点位的O_(3)-8 h浓度分布变化大致分为单峰型和持续递减型,浓度主要集中在40~80μg/m^(3);国控点和省控点的臭氧浓度时间分布趋势一致,空间分布存在区域性差异;全市20个区县(开发区)的臭氧污染呈现南北中心城区高、东西远郊区低的空间分布特征。总之,西安市臭氧污染的时空分布主要受到气象条件、污染物排放和城市布局差异的综合性影响。

This study analyzed the temporal and spatial distribution characteristics of ground ozone in Xi’an based on the air quality monitoring data during 2016-2020.Overall,the ozone concentration in Xi’an was slightly higher than the national average.The temporal distribution characteristics of ozone concentration showed that the average annual concentration in Xi’ an increased from 2016 to 2018 and then decreased slightly.In each year,the monthly mean concentration exhibited obvious seasonal variation characteristics.In June,the number of days exceeding the standard and the average concentration of ozone reached the peak.The diurnal variation pattern of ozone concentration was consistent throughout the year regardless of the seasons,showing a unimodal pattern.The hour-averaged concentration reached its peak between 15:00 to 16:00.There was a negative correlation between ozone and NO_(2) or CO.As shown by the eight-hour ozone concentration from 12 state controlling sites,the spatial distribution of ozone concentration also exhibited unimodal or continuous decreasing pattern.In each district,the relative frequency of ozone concentration reached the peak at 40 to 80 μg/m~3.The temporal distribution trend of ozone concentration was consistent at state and provincial controlling sites,but the spatial distribution showed regional variations.Judging from the 20 districts and counties in Xi’an city,the ozone pollution was high in the central urban area and low in the eastern and western suburban areas.In summary,the spatial and temporal distribution of ozone pollution in Xi’an were mainly affected by multiple factors including meteorological conditions,pollutant emissions and urban layout differences.