Abstract
Abstract. In the present study, the WRF-CHEM model is used to evaluate the contributions of trans-boundary transport to the air quality in Beijing during a persistent air pollution episode from 5 to 14 July 2015 in Beijing–Tianjin–Hebei (BTH), China. Generally, the predicted temporal variations and spatial distributions of PM2.5 (fine particulate matter), O3 (ozone), and NO2 are in good agreement with observations in BTH. The WRF-CHEM model also reproduces reasonably well the temporal variations of aerosol species compared to measurements in Beijing. The factor separation approach is employed to evaluate the contributions of trans-boundary transport of non-Beijing emissions to the PM2.5 and O3 levels in Beijing. On average, in the afternoon during the simulation episode, the local emissions contribute 22.4 % to the O3 level in Beijing, less than 36.6 % from non-Beijing emissions. The O3 concentrations in Beijing are decreased by 5.1 % in the afternoon due to interactions between local and non-Beijing emissions. The non-Beijing emissions play a dominant role in the PM2.5 level in Beijing, with a contribution of 61.5 %, much higher than 13.7 %, from Beijing local emissions. The emission interactions between local and non-Beijing emissions enhance the PM2.5 concentrations in Beijing, with a contribution of 5.9 %. Therefore, the air quality in Beijing is generally determined by the trans-boundary transport of non-Beijing emissions during summertime, showing that the cooperation with neighboring provinces to mitigate pollutant emissions is key for Beijing to improve air quality.
Highlights
Beijing, the capital of China, has become an environmentally stressed city due to a growing population, increasing transportation activity, and city expansion (Parrish and Zhu, 2009)
A persistent air pollution episode with high concentrations of O3 and PM2.5 is simulated using the WRF-CHEM model during the period from 5 to 14 July www.atmos-chem-phys.net/17/2035/2017/
The APPCAP has been implemented since 2013 September, the average O3 concentration in the afternoon has increased by 22.8 % from 2013 to 2015 in Beijing, and Beijing still experienced high O3 and/or PM2.5 concentrations frequently during summertime of 2015
Summary
The capital of China, has become an environmentally stressed city due to a growing population, increasing transportation activity, and city expansion (Parrish and Zhu, 2009). Beijing is situated in northeastern China, surrounded from the southwest to the northeast by the Taihang Mountains and the Yanshan Mountains and open to the North China Plain (NCP) in the south and east. The NCP has become one of the most polluted areas in China due to rapid industrialization and urbanization (Zhang et al, 2013). When south or east winds are prevalent in the NCP, air pollutants originating in the NCP are transported to Beijing and surrounding areas and subject to accumulation due to the mountain blocking, causing heavy air pollution in Beijing (Long et al, 2016). PM2.5 (fine particulate matter) and O3 (ozone) are considered to be the most serious air pollutants of concern in Beijing during summertime (e.g., Xie et al, 2015; Zheng et al, 2015; Chen et al, 2015; Wang et al, 2016).
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