The Influence Of Traffic Restriction Measures On Air Quality In Lanzhou City Based On CMAQ

In November 2016,the traffic restriction measures on motor vehicles were implemented for the sustained serious air pollution in accordance with the"Lanzhou air pollution emergency plan".However,traffic restrictions not only cost a lot of government financial funds,but also influence the daily travel of the public.The effectiveness of traffic restriction measures for air quality improvement has attracted widespread attention from the community.Therefore,the investigation of mobile pollution sources was conducted and,the air quality model was used to explore the sensitivities of traffic restrictions measures to air quality and evaluate the effectiveness of traffic restriction measures in emergency plans quantitatively.It is significant for government to optimize emergency response measures and take effective measures to further improve the air quality in Lanzhou.The study area is the main urban area of Lanzhou city,and the research period is November 13to November 19 and November 20 to November 26.According to the emission coefficient method in the“Technical guide for the compilation of emission inventory for air pollutants from road vehicles（Trial）”,the high resolution emission inventory of road vehicles of Lanzhou main urban in2016 was compiled by GIS combining with the measured road traffic data and local parameters such as temperature and height.The WRF model was used to simulate the meteorological field in the main urban area of Lanzhou city with localized parameterization scheme,then the CMAQ air quality model was applied to simulate the impact on the air quality of the study area under the three scenarios,which were without adopting even-odd traffic restriction measures,only adopting even-odd traffic restriction measures and all measures in Lanzhou air pollution emergency plan.From the analysis of simulating results,the mobile pollution sources had great contribution to NO₂ and CO and less contribution to PM10 and primary PM2.5 without adopting even-odd traffic restriction measures.The average contribution rate of mobile pollution sources to NO₂ CO,PM10,PM2.5 in the four air quality national control points were 22.95%-36.80%,8.33%-13.92%,0.68%-0.88%,1.10%-1.52%during the simulating period,respectively.When only even-odd traffic restriction measures was adopted from the 13th to the 19th,NO₂and CO emissions from mobile pollution sources in the main urban of Lanzhou were effectively reduced,and the effect on PM10 and primary PM2.5 reduction was not obvious.The average contribution rate of mobile pollution sources to NO₂ in this case was 14.63%-26.55%during the simulating period,which was 8.32%-10.45%lower than the previous value;the average contribution rate to CO was 4.26%-7.04%,which was 4.07%-6.88%lower than the previous value;the average contribution rate to PM10 was 0.63%-0.77%,which was 0.05%-0.11%lower than the previous value;the average contribution rate to primary PM2.5 was 1.00%-1.32%,which was0.10%-0.20%lower than the previous value.When all measures in Lanzhou air pollution emergency plan were adopted from the 20th to the26th,the average contribution rate of mobile pollution sources to NO₂,CO,PM10,PM2.5 in the four air quality national control points of Lanzhou main urban were 11.49%²1.80%,12.46%¹8.86%,0.98%¹.29%,1.66%².20%.during the simulating period,respectively.The research results showed that the mobile pollution sources had a greater contribution to NO₂and CO in air quality of Lanzhou main urban,and a smaller contribution to PM10 and primary PM2.5.The traffic restriction measures can effectively reduce the pollution of NO₂ and CO caused by mobile pollution sources to the main urban of Lanzhou,and it was not obvious for PM10 and primary PM2.5.