Journal
SCIENCE OF THE TOTAL ENVIRONMENT
Volume 704, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.scitotenv.2019.135210
Keywords
Synoptic situations; PM2.5; BTH
Categories
Funding
- National Natural Science Foundation of China [41275101, 41430424]
- Fundamental Research Funds for the Central Universities of China
- National Key R&D Plan (Quantitative Relationship and Regulation Principle between Regional Oxidation Capacity of Atmospheric and Air Quality) [2017YFC0210000]
- National Research Program for Key Issues in Air Pollution Control [DQGG0105]
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Meteorological conditions play a key role in formation of air pollution, determining dispersion or accumulation of air pollutants. Aggressive emission mitigation measures have been taken recently in the Beijing-Tianjin-Hebei region (BTH), China, but pervasive and persistent haze still frequently engulfs this region during wintertime. Occurrence frequency of unfavorable meteorological conditions in winter is anticipated to constitute a significantly important factor in driving the heavy haze formation in BTH. Large scale synoptic patterns influencing BTH during the wintertime from 2013 to 2017 are categorized into six types, including north-low, southwest-trough, southeast-high, southeast-trough, transition, and inland-high using the NCEP reanalysis data. Southwest-trough and southeast-high are defined as favorable synoptic patterns and the remaining four categories are unfavorable ones based on FLEXPART simulations. Compared to measurements of fine particulate matter (PM2.5) in BTH, favorable synoptic conditions generally correspond to the low level or decreasing trend of PM2.5 concentrations while under unfavorable conditions PM2.5 concentrations are high or increasing. Occurrence of wintertime haze episodes in BTH correlates well with the evolution trend of unfavorable synoptic patterns from 2013 to 2017 although the anthropogenic emissions have substantially decreased. PM2.5 concentrations also exhibit correlations with local meteorological elements, including winds, temperature, and relative humidity, which are ultimately steered by large scale synoptic situations. The WRF-Chem model simulations further reveal the critical role of large-scale synoptic patterns in the heavy haze formation. Overall, under unfavorable synoptic situations, emission mitigation is the best choice to improve the air quality in BTH. (C) 2019 Elsevier B.V. All rights reserved.
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