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| Effects of emission-sources reduction at different time points on PM2.5 concentration over Beijing Municipality |
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Abstract The Models-3Community Multi-scale Air Quality (CMAQ) Modeling system with a high resolution inventory data over Beijing-Tianjin-Hebei area was used to investigate the effects on PM2.5 concentrations over Beijing of emission-sources reduction, with the same reduction rate at 5different time points: 4 days, 3 days, 2 days, 1 day and 0 day in advance of the most polluted day. Simulations were made for a representative air pollution episode (Feb 7th~16th, 2012), in which Feb 13th was found to be the most polluted day. The results show that the PM2.5 concentration was likely to decline more significantly if emission-sources reduction measures were taken before the most polluted day than were taken on the most polluted day. In addition, the earlier emission-sources reduction measures were taken, the more significantly the PM2.5 concentration would decline. Reducing emission-sources 1 day, 2 days, 3 days ahead of the most polluted day led to declination of the peak value of PM2.5 concentration at the Haidian station by 23%, 31%, and 39%, and in urban Beijing by 22%, 30%, and 38%, respectively. However, as the number of days ahead of the most polluted day (Feb 13th) to take reduction measures increased further, the additional decrease of the peak PM2.5 concentration became smaller, thus the emission-sources reduction benefits became less effective. The peak PM2.5 concentration would decrease by 40% and 39% at Haidian station and urban Beijing if the reduction measures were taken 4 days before the most polluted day, which shows almost no improvement compared with those 3days in advance. Similar results were obtained in simulations for another pollution episode (Jan 11th~20th, 2012). For controlling severe air pollution, both reduction costs and benefits should be considered. Our study indicates that the most effective way of emission-sources reduction is to take reduction actions 2~3days ahead of the possible severe pollution event, which can be obtained from meteorological condition prediction. In this way, substantial decrease of the peak PM2.5 concentration can be achieved with less cost for implementing the reduction measures.
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Received: 18 September 2013
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