Numerical study of the PM2.5 emission control from "APEC Blue" to "Beijing Blue" by WRF-SMOKE-CMAQ model system

In the year 2014, the APEC meeting was hold in Beijing, where the fine particulate matter (PM2.5) concentration is high and worried. The government can take necessary short-term emissions reduction measures to improve air quality. According to Wu et al. (2014), a new air quality forecast model system, based on WRF-SMOKE-CMAQ model, was established before APEC. The model system plays good performance in October 2014, catches four air pollution episodes and has a high correlation coefficient of 0.89. And the daily forecast of PM2.5 concentration reaches 277 µg m^-3 and close to the observed value (320 µg m^-3 ), but still a little underestimated. The forecast result indicates the emissions inventory used in the model system is reasonable as baseline scenario, which scenario without any emission-sources reduction. From 3 to 12 November, the emission-sources reduction measures, e.g. the factory cut production and closures, are carried step by step in Beijing and its surrounding areas. Those measures information is collected, corrected and used in the SMOKE model to prepared as a reduced emissions inventory as APEC scenario. The same WRF-CMAQ model system, but be driven by the emission inventory of APEC scenario, is used to simulate the air quality under such emission-sources reduction measures, and evaluate the effect of emission-sources reduction during APEC 2014 in Beijing. According to the results, the daily PM2.5 concentrations would reduce from 107 µg m^-3 in the baseline to 72 µg m^-3 in the APEC scenario, while the observed is 69 µg m^-3 on 8 November. From 6 to 10 November, the observation is lower than the forecast results in the baseline scenario, that indicates the emission-sources reduction measures effects in the air quality in Beijing, if we trust the model. We also found that the observation on 7-8 November even lower than the forecast results in the APEC scenario, which indicates the emission reduction efforts more than expected. In the past year 2017, the similar emission-sources reduction measures are carried but cover the whole autumn and winter in 2017/2018, and the annual PM2.5 concentration reaches to 58 μg m-3, while the "Beijing Blue" frequently appears.