Simulated Sensitivity of Ozone Generation to Precursors in Beijing during a High O_(3) Episode

This study uses the WRF-Chem model combined with the empirical kinetic modeling method(EKMA curve)to study the compound pollution event in Beijing that happened in 13−23 May 2017.Sensitivity tests are conducted to analyze ozone sensitivity to its precursors,and to develop emission reduction measures.The results suggest that the model can accurately simulate the compound pollution process of photochemistry and haze.When VOCs and NOx were reduced by the same proportion,the effect of O_(3)reduction at peak time was more obvious,and the effect during daytime was more significant than at night.The degree of change in ozone was peak time>daytime average.When reducing or increasing the ratio of precursors by 25%at the same time,the effect of reducing 25%VOCs on the average ozone concentration reduction was most significant.The degree of change in ozone decreased with increasing altitude,the location of the ozone maximum change shifted westward,and its range narrowed.As the altitude increases,the VOCs-limited zone decreases,VOCs sensitivity decreases,NOx sensitivity increases.The controlled area changed from near-surface VOCs-limited to high-altitude NOx-limited.Upon examining the EKMA curve,we have found that suburban and urban are sensitive to VOCs.The sensitivity tests indicate that when VOCs in suburban are reduced about 60%,the O_(3)-1h concentration could reach the standard,and when VOCs of the urban decreased by about 50%,the O_(3)-1h concentration could reach the standard.Thus,these findings could provide references for the control of compound air pollution in Beijing.

Chemical characterization and source identification of PM_(2.5) in Luoyang after the clean air actions

Luoyang is a typical heavy industrial city in China,with a coal-dominated energy structure and serious air pollution.Following the implementation of the clean air actions,the physic-ochemical characteristics and sources of PM_(2.5) have changed.A comprehensive study of PM_(2.5) was conducted from October 16,2019 to January 23,2020 to evaluate the effectiveness of previous control measures and further to provide theory basis for more effective policies in the future.Results showed that the aerosol pollution in Luoyang in autumn and win-ter is still serious with the average concentration of 91.1 μg/m^(3),although a large reduction(46.9%)since 2014.With the contribution of nitrate increased from 12.5%to 25.1%and sul-fate decreased from 16.7%to 11.2%,aerosol pollution has changed from sulfate-dominate to nitrate-dominate.High NO_(3)^(-)/SO_(4)^(2-)ratio and the increasing of NO_(3)^(-)/SO_(4)^(2-)ratio with the aggravation of pollution indicating vehicle exhaust playing an increasingly important role in PM_(2.5) pollution in Luoyang,especially in the haze processes.Secondary inorganic ions contributed significantly to the enhancement of PM_(2.5) during the pollution period.The high value of Cl^(-)/Na^(+)and EC concentration indicate coal combustion in Luoyang is still serious.The top three contributor sources were secondary inorganic aerosols(33.3%),coal combus-tion(13.6%),and industrial emissions(13.4%).Close-range transport from the western and northeastern directions were more important factors in air pollution in Luoyang during the sampling period.It is necessary to strengthen the control of coal combustion and reduce vehicle emissions in future policies.