2015~2020年济南市O_(3)污染趋势及敏感性变化分析

Changes in Ozone Pollution Trend Characteristics and Sensitivity in Jinan from 2015 to 2020

基于环境空气质量站点监测数据及卫星遥感资料,研究了2015~2020年济南市近地面臭氧(O_(3))污染的时空分布特征、变化趋势和前体物生成敏感性.结果表明,2015~2020年济南市O_(3)浓度呈上升趋势,全年O_(3)日最大8 h滑动平均值(MDA8)的第90百分位数(即年评价浓度)和4~9月MDA8 O_(3)浓度年均值分别以4.8μg·(m^(3)·a)^(-1)和3.8μg·(m^(3)·a)^(-1)的速率增长;各监测站点间O_(3)浓度水平差异逐渐缩小,且O_(3)浓度高值范围进一步扩大,济南市有16.1%和22.6%的监测点年评价值和4~9月MDA8 O_(3)出现了显著的正趋势(P<0.05),这些监测站点主要位于市区和靠近市区的郊区.卫星遥感监测数据显示2015~2020年4~9月济南市NO_(2)对流层柱浓度下降20.6%,年下降速率为0.3×10^(15)mole·(cm^(2)·a)^(-1),特别是城区及周边下降幅度较大,而HCHO柱浓度未见明显下降趋势,表明NO_(x)的减排量远大于VOCs的减排量,这种对O_(3)前体物NO_(x)/VOCs不恰当的控制比例导致济南市O_(3)总体呈上升的趋势.当前济南市VOCs的控制力度远远不够,未来应通过增加VOCs减排,加大VOCs/NO_(x)控制比例,以进一步有效控制O_(3)污染,尤其是城区及周边郊区.

The surface ozone(O_(3))spatiotemporal distribution,variations,and its causes in Ji’nan from 2015 to 2020 were revealed based on the air quality monitoring network data and satellite retrievals from the Ozone Monitoring Instrument(OMI).The results showed that the ozone concentration in Ji’nan gradually increased from 2015 to 2020.The annual 90th percentile of the daily maximum 8-h average(MDA8)O_(3)(namely the annual evaluation value)and the MDA8 O_(3)(April-September)increased by 4.8μg·(m^(3)·a)^(-1)and 3.8μg·(m^(3)·a)^(-1),respectively.The trend of the ozone levels in the high-concentration range increased faster than that in the low-concentration range.The MDA8 in June increased by 7.4μg·(m^(3)·a)-1,and the rate range of increases was 2.6-3.9μg·(m^(3)·a)^(-1)in the cool seasons(December-February);thus,the O_(3)control in winter cannot be ignored.It is apparent from the diurnal variations in ozone from 2015 to 2020 in April-September that the average ozone levels have risen in recent years.The growth rate in the daytime was higher than that at night.The capacity of photochemical production has been increasing,especially in recent years.Additionally,it is noteworthy that the peak time for ozone levels occurred approximately 1-2 h earlier.The disparity of ozone concentrations among different stations gradually decreased in recent years.Compared with that in 2015,the range of areas with high O_(3)concentrations in 2019-2020 was further expanded.The significant positive trends in MDA8-90th and MDA8(April-September)were observed in 16.1%and 22.6%of the monitoring sites in Ji’nan(P<0.05),most of which were located in urban areas and the suburbs close to urban areas.The temporal and spatial changes in ozone in Jinan had been affected by the changes in VOCs and NO_(x)emissions since 2015.Satellite remote sensing data from 2015 to 2020 revealed that the NO_(2)tropospheric columns(April-September)showed reductions of 20.6%,with a decreasing rate of 0.3×10^(15)mole·(cm^(2)·a)^(-1),especially in the urban areas and suburbs.The detected variation trends of tropospheric HCHO were weak and insignificant,which suggested that the decrease in NO_(x)emissions was much greater than the decrease in VOCs emissions,and the gap had become more obvious in the urban areas.With responses to precursor emissions,the chemical sensitivity of O_(3)formation had been changing.The VOCs-limited regimes continuously decreased,and the mixed NO_(x)/VOCs-sensitive regimes and NO_(x)-limited regimes increased.In general,such an extremely inappropriate control ratio of ozone precursor NO_(x)/VOCs led to an overall trend of slow increasing fluctuations of O_(3)in Ji’nan.The findings clearly indicate that the reduction of VOCs in Ji’nan was far from sufficient,and strengthening the current control of VOCs emissions is an effective measure to control the growth trend of O_(3)pollution in Ji’nan in the near future,especially in urban and surrounding suburban areas.