Abstract
ABSTRACTIn December 2015, the Beijing-Tianjin-Hebei (BTH) region experienced several episodes of heavy air pollution. Beijing municipal government therefore issued 2 red alerts on December 7 and 19, respectively, and also implemented emergency control measures to alleviate the negative effects of pollution. It is estimated that the heavy pollutions in 2 red alert periods in Beijing were due mainly to the accumulation of air pollutants from local emission sources and the transboundary transport of pollutants from surrounding areas. The collected meteorological and PM2.5 data indicate that the severity of air pollutions were enlarged by the poor meteorological conditions along with lower mixing layer height. In this study, the WRF-CAMx modeling system was utilized not only for analyzing the contributions of PM2.5 from different sources, but also for quantitatively assessing the effects of implementing various emergency control measures on PM2.5 pollution control during the red alert periods. The modeling results show that local emissions were the most dominant contributors (64.8%–83.5%) among all emission sources, while the main external contributions came from the city of Baoding (3.4%–9.3%). In addition, among 5 different emission source categories, coal and traffic were the two dominant contributors to PM2.5 concentration in urban area of Beijing. Then four pollution control scenarios were designed particularly to investigate the effectiveness of the emergency control measures, and the results show that, generally these emergency control measures have positive effects on air pollution reduction. In particular, restrictive measures of traffic volume control and industrial activity shutdown/suspension have been found as the most effective measures in comparison to other emergency control measures. It is recommended that such effective measures should be considered to implement when next time similar heavy air pollutions occur in the city of Beijing.
Highlights
As the political and cultural center of China, Beijing has made and implemented an ambitious urban development plan over the past two decades to transform an old and historical city to a new and modern metropolis (Dong et al, 2013)
Meteorological Conditions and PM2.5 Evolution Characteristics in December 2015. It is evident from the previous studies that PM2.5 concentration is influenced by meteorological conditions, and the maximum layer height (MLH) is considered to be an important factor causing the variance of PM2.5 concentrations (Yang et al, 2015a)
In December 2015, 2 red alerts were issued by Beijing municipal government and various emergency control measures were implemented in the BTH region to alleviate the negative effects of severe air pollutions occurred in Beijing
Summary
As the political and cultural center of China, Beijing has made and implemented an ambitious urban development plan over the past two decades to transform an old and historical city to a new and modern metropolis (Dong et al, 2013). During the aforementioned international events (i.e., 2008 Beijing Olympic Games (Wang et al, 2009; Wang et al, 2014b), 2014 APEC Summit (Chen et al, 2015b)), massive emission control measures were designed collectively by the governments of Beijing and surrounding provinces, and more importantly, were implemented a few weeks prior to the events; as a result, the air quality of Beijing was generally improved to good conditions and the PM2.5 concentrations were at low levels. As an extension of previous efforts in this area, in this study, the CAMx modeling system is used for the first time to simulate the regional air quality system in BTH region during 2 red alert periods and answer various questions relating to PM2.5 pollution occurred in Beijing.
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