| The atmospheric combined pollution,which takes the fine particulate matter(PM2.5)and ozone(O3)as the key pollutants,has gradually become the major issue of air pollution prevention and control in China at present.Meteorological conditions play an important role in the formation of PM2.5 and O3 pollution.Quantifying the key processes of meteorological conditions affecting PM2.5 and O3,identifying the major meteorological factors,and exploring the impacts of climate change on PM2.5 and O3 concentrations are important prerequisites for formulating scientific measurements of emission reduction to effectively improve air quality.In this work,under the combination with ambient monitoring data,the regional air quality model WRF/CMAQ was used as a main tool to investigate the sensitivity of particulate matter and ozone pollution to various meteorological factors.The response of PM2.5 and O3concentrations in the past decade to meteorological variations and emission control was also quantitatively estimated.In addition,the required emission reduction,for eliminating regional heavy pollution under the extreme meteorological conditions,was discussed.Furthermore,the effects of 1.5K warming on biogenic volatile organic compounds(BVOCs)emission,ozone exposure and the atmospheric oxidizing capacity,were quantitatively evaluated.The main results are as follows:Firstly,the sensitivity of fine particulate matter and ozone to different meteorological parameters was quantitatively evaluated.Using the mesoscale weather forecast model WRF,the temperature,wind speed,absolute humidity,boundary layer height,cloud liquid water content and precipitation of various meteorological factors were varied to different degrees.The sensitivity of PM2.5 and O3 concentrations to individual meteorological factors in winter(January)and summer(July)of 2013 was analyzed.From the seasonal scale,the background concentration of PM2.5 is higher in winter,so the sensitivity is higher than that in summer.However,there is little difference in the sensitivity of O3 in summer,for example,its sensitivity to temperature is about+2 ppb/k.From the spatial scale,the sensitivity of PM2.5 to temperature,wind speed,boundary layer height and precipitation in most areas of China is negative,and the sensitivity to absolute humidity and cloud liquid water content is positive.the effect of temperature on O3 is dependent on the O3 formation chemistry(net O3 formation areas)or O3consumption chemistry(net O3 loss areas).In most areas in winter,the sensitivity of wind speed and boundary layer height is positive and the sensitivity of absolute humidity is negative.In summer,the sensitivity of wind speed is positive and negative,and the boundary layer height is just opposite.Except Yunnan Province,the absolute humidity is negative,so the sensitivity to cloud liquid water content and precipitation can be neglected.Among these meteorological factors,temperature,wind speed,absolute humidity and boundary layer height play a key role in the change of PM2.5 concentration.In winter,it mainly affects the secondary inorganic components,and the sensitivity value is larger in Chongqing.In summer,it is mainly reflected by the influence of secondary inorganic and organic aerosols,and the sensitivity of Beijing is more prominent.In addition to liquid water content and precipitation,the sensitivity of O3 is very important to the response of temperature,wind speed,boundary layer height and absolute humidity.By studying which meteorological factors PM2.5 and O3 are most sensitive to,it is helpful to determine the key factors in inter-annual meteorological conditions that may affect air quality.Secondly,the influence of meteorological conditions and emission changes on the fine particulate matters and ozone in China is analyzed.Based on the environmental monitoring data and regional chemical transport model WRF/CMAQ,we simulated atmospheric pollutant concentrations from 2011 to 2020 with fixed emissions in 2016,and analyzed the responses of PM2.5 and O3 concentrations to emission control and meteorological changes in all provincial capitals of China in 2013,2016 and 2019.Over time,China's air pollution control measures have been effective.In the winter of 2016 and 2019,the PM2.5 concentration decreased by 12.7?g/m3 and 43.9?g/m3,respectively.The annual average PM2.5 concentration decreased by about18.0?g/m3,which will be offset by unfavorable weather conditions.Especially in extreme pollution events,the negative effects of adverse meteorological conditions are quite significant.For example,in December 2016,the meteorological factors drove a significant increase in PM2.5 concentration in North China(28.2?g/m3),and in December 2019,the concentration in East China increased by 28.2?g/m3.Compared with 2013,the decrease of PM and gaseous precursors in summer 2016 led to an increase of 6.6 ppb in the average MDA8 O3 concentration in provincial capital cities,while meteorological contribution was relatively small.When China's emission control measures shifted to the center of gravity of volatile organic compounds(VOCs),in summer of 2019,the O3 concentration in different areas decreased by 1.6?7.8 ppb,but the adverse meteorological conditions aggravated O3 pollution by about 6.9 ppb.This study discussed the impact of changes in conditions on air pollution,verified the effectiveness of China's measures from a key emission reduction of particulate matter to the transfer of VOCs and NOx coordinated control strategy,and emphasized the importance of meteorological and PM2.5 precursor emission reduction for improving air quality when controlling O3 pollution.Thirdly,the emission threshold of heavy pollution elimination process under extremely adverse meteorological conditions is determined.Meteorological conditions determine the atmospheric environmental capacity of region.Based on the sensitivity simulation of"fixed emissions and climate change",we screened out PM2.5 heavy pollution(>150?g/m3)weather for Beijing-Tianjin-Hebei,Yangtze River Delta,Chengdu-Chongqing and Fenwei Plain.We found that the weather of heavy pollution in these years has common features,such as low temperature,low wind speed,high relative humidity,low boundary layer height and no precipitation.Moreover,the PM2.5 pollution days corresponding to the worst weather conditions in the region all occur in winter,and the concentration can reach 213.0?405.2?g/m3.By limiting the upper limit of the emission reduction ratio of air pollutants by 20%?80%,it is found that in the Beijing-Tianjin-Hebei region with the highest emission intensity,at least 60%emission reduction is needed to completely eliminate regional heavy pollution incidents.Compared with the actual emission list,the emission of air pollutants is reduced by 40%,which is helpful to eliminate heavy pollution in the Yangtze River Delta region.20%reduction can avoid heavy pollution in Chengdu-Chongqing and Fenwei plain.If all cities in the region are to be able to eliminate heavy pollution and meet air quality standards,the government will need to tighten controls and step up efforts to reduce emissions.Fourthly,the effects of 1.5K warming on atmospheric oxidizing capacity and vegetation ozone exposure in China were studied.Considering the impact of global warming,the effects of temperature increase of 1.5K on the emission of biogenic volatile organic compounds(BVOCs)and atmospheric chemical process,and then on the atmospheric oxidizing capacity(AOC)and O3 were discussed.From the perspective of the spatial distribution of O3,the average daily concentration of O3 is higher in the west and northwest China in summer,and the MDA8 O3 concentration and air quality exceeding standard days are higher in eastern China.Under 1.5K temperature rise,the atmospheric oxidizing capacity of ozone(AOC?O3)increased relatively little,the atmospheric oxidizing capacity of ONOO-radical(AOC?·NO3)increased the most,and the atmospheric oxidizing capacity of·OH radical(AOC?·OH)also increased significantly.Under the influence of temperature and BVOCs,the concentration of MDA8 O3and days of ozone exceeding standard in North China Plain,Yangtze River Delta,Pearl River Delta(hereinafter referred to as Pearl River Delta)and Chengdu-Chongqing area increased by?3ppb and 15 days,respectively.M7(average ozone exposure index of 7 hours during daytime(09:00-15:00))showed a similar trend to M24(24-hour average index of the whole day),but its value changed significantly higher than that of M24.Over the North China Plain,N100(the number of hours in which hourly ozone concentrations exceed 100 ppb)increased by about80%.W126(the weighted sum of O3 concentration in April-October)is slightly higher than SUM60(the sum of O3 concentration above 60 ppb in 90 days from 08:00 to 20:00)and AOT40f(the sum of O3 concentration above 40 ppb from 06:00 to 21:00).But the spatial distribution is similar.In four typical regions(Beijing-Tianjin-Hebei,Yangtze River Delta,Pearl River Delta and Sichuan Basin),the individual impact driven by warming is generally higher than the contribution of BVOCs change.Although the influence of BVOCs emission change on O3 level is small,it will lead to the increase of O3 concentration in different degrees in all regions,which indicates that it is necessary to consider the influence of climate change on BVOCs emission.Based on the analysis and results above,this work quantitatively evaluates the sensitivity of fine particulate matter and ozone to different meteorological factors,the contributions of emissions and meteorological conditions to ground-level of PM2.5 and O3 in China in recent years,and the required emission reductions in eliminating regional heavy pollution under extremely adverse meteorological conditions,respectively.Besides,the possible changes of atmospheric oxidizing capacity and ozone exposure,due to the 1.5K temperature increase in the future,were also analyzed.Comprehensively understanding the interaction between meteorology and air pollutants by investigating the complex elements of the inter-annual meteorological conditions,local meteorological factors,and future climate,has a guiding significance.In the meantime,this study can provide theoretical and technical support to actively cope with air pollution and formulate emission control strategies in China. |
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