Model Simulation Of The Impact Of Different Emission Scenarios On The Air Quality In Beijing And Its Surrounding Areas

Both meteorology and emission control are key factors in affecting the air quality.A large variety of emission control measures have been implemented to ensure the improvement of air quality for the period of Asia-Pacific Economic Cooperation（APEC）China 2014,which provides us an ideal test-bed to determine how these measures affect air quality in Beijing and surrounding areas.Based on hourly observations at eight monitoring sites of Beijing,the concentrations of other primary atmospheric pollutants during APEC were found to have significantly lower magnitudes than those before APEC,except for a higher O₃concentration.Overall,WRF/Chem reproduced very well the observed time series of PM_2.5,PM₁₀,NO₂,CO,O₃.To investigate the impact of emission control measures on air quality on both local and regional scales,four emission control schemes were designed according to the locations where emission reduction had taken place,then the corresponding simulations were run separately.The scheme of S2（emission control implemented in Beijing）results in a reduction of 22%,24%,10%and 22%for the concentrations of PM_2.5,PM₁₀,NO₂ and CO,as compared with 14%,14%,8%and 13%for scheme S3（emission control implemented out of Beijing）.This indicates that the reduction in local pollution emission in Beijing contributes more to the improved air quality in Beijing during APEC China 2014 than does that from outside Beijing.In terms of the impact on regional scale,the real emission control scheme leads to significant reduction of PM_2.5 in the whole domain.Either emission reduction measures implemented in Beijing（S2）or those implemented outside of Beijing（S3）favor the larger reduction in PM_2.5 in the domains where measures are presumably taken.Besides,based on model simulation using the CMA（China Meteorological Administration）Unified Atmospheric Chemistry Environment for aerosols（CUACE/Aero）,in combination with simultaneous ground-based hourly PM_2.5 observations,we aim to quantify the relative contributions of the emission control measures and meteorology to the blue-skies seen in Beijing during APEC.A series of model simulations have been performed over Beijing-Tianjin-Hebei（BTH）region by implementing nine different emission control schemes.To figure out the relative contributions of the emission control measures and meteorology,the study period has been divided into five episodes.Overall,the CUACE/Aero model can reasonably well reproduce the temporal and spatial evolution of PM_2.5 during APEC 2014,although the model performance varies by different time periods and regions of interest.Model results show,among all the emission control measures under investigation,local emission control in Beijing contributed the largest to the reduction of PM_2.5concentrations,including a reduction of 35%in urban area of Beijing and 34%in Huairou,which is a higher value than that WRF-Chem has given,in contrast to the vehicle emission control in Hebei that contributed the least with a reduction of less than 1%.The emission control measures and meteorology alternated to dominate the absolute reduction of PM_2.5concentrations.When the weather conditions are unfavorable for dispersion of air pollution,emission control measures outperformed meteorology with a reduction of 55.3⁵9.4μg/m³ in urban area of Beijing and 32.5³3μg/m³ in Huairou.Conversely,when the northwesterly winds prevailed,meteorology tends to outweigh the role of emission control in accounting for the drop of PM_2.5.The atmospheric dilution conditions are determined through the model calculation of the mass inflow of PM_2.5 per unit volume near the surface.To improve the air quality in Beijing,much more coordinated efforts,therefore,should be made combined with weather conditions,particularly in the aspect of more stringent reduction and control strategy on pollutant emission sources across the NCP.Our findings have significant implications for effective planning and implementation of emission control measures in the future.