Abstract
. Beijing occurred severe haze events in winter of recent years. To understand the extreme events, the air pollution case from 9 January to 15 January 2019 was selected. The PM2.5concentration of 34 monitoring sites which were hourly measured, the nationwide synoptic conditions at surface and 850hpa, the meteorological factors including temperature, wind speed and humidity and the vertical variation in Planetary boundary layer (PBL) during the case were analyzed. It is found that synoptic condition, meteorological factors and urban PM2.5(fine particles with diameter less than 2.5μm) concentration distribution changed regularly with time. Clean stage, transport stage, cumulative stage and dispersion stage during haze are defined in this study. Three overall research results are: (1) The synoptic variation is distinct. Beijing is alternately dominated by Siberian High-pressure and Western Pacific Subtropical High-pressure system in winter. The transport stage is with predominant Subtropical High-pressure which brings temperature and humidity rise. High humidity facilitates formation of secondary aerosols. The cumulative stage ends along with boosted Siberian High-pressure. (2) The severe haze is characterized by temperature inversion, low wind speed and high humidity, especially nearby surface, and experienced PM2.5explosive growth. The stability of PBL structure will be strengthened with decreased PBL height, which inhibits the dispersion of pollutants. (3) The PM2.5concentrations during different stages had different regional distribution. The southern PM2.5concentration is much high than northern in transport stage. During dispersion stage, urban central PM2.5is the high for the reason that buildings, vehicle exhaust and urban heat island effects all impedehaze disappearing.
Highlights
Air pollution became a significant challenge in the world, especially in developing countries ([1])
Meteorological factor is the major cause of heavy haze pollution in Beijing and affected by synoptic variation
It is important to understand the comprehensive mechanism that different meteorological affects the PM2.5 concentration and how meteorological factors change with the variation in synoptic background
Summary
Air pollution became a significant challenge in the world, especially in developing countries ([1]). Previous studies by analyzing the atmospheric background suggested that disadvantageous meteorological effects including temperature inversion, high relative humidity, weak surface wind and vertical wind shear all substantially influenced the PM2.5 concentration, through both physical (e.g., transportation, dispersion and deposition) and chemical (e.g., the formation pathway and reaction rate of secondary aerosol) mechanism ([19,20]). This paper will focus on the haze process in Beijing by using the PM2.5 concentration observation data of 34 monitoring sites which records severe pollution episode in January 2019 in particular from January 9 to 15, analyze the synoptic condition and the structure of PBL, explore the interaction and correlation between the spatial distribution feature of PM2.5 and meteorological elements in Beijing during different stages of the haze pollution case
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