Abstract
Severe haze events have many adverse effects on agricultural production and human activity. Haze events are often associated with specific patterns of atmospheric circulation. Therefore, studying the relationship between atmospheric circulation and haze is particularly important for early warning and forecasting of urban haze events. In order to study the relationship between multi-scale atmospheric circulation and severe haze events in autumn and winter in Shanghai, China, we used a T-mode objective classification method to classify autumn and winter atmospheric circulation patterns into six types based on sea level pressure data from 2007 to 2016 in the Shanghai area. For the period between September 2016 and February 2017, we used the Allwine–Whiteman method to classify the local wind in Shanghai into three categories: stagnation, recirculation, and ventilation. By further studying the PM2.5 concentration distribution, visibility distribution, and other meteorological characteristics of each circulation type (CT) and local wind field type, we found that the Shanghai area is most prone to severe haze when exposed to certain circulation patterns (CT1, CT2, and CT4), mainly associated to the cold air activity and the displacement of the high pressure system relative to Shanghai. We also found that the local wind fields in the Shanghai area are dominated by recirculation and stagnation events. These conclusions were further verified by studying a typical pollution process in Shanghai in November 2016 and the pollutant diffusion path using the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory model) simulation model.
Highlights
Haze is a weather phenomenon that occurs when the aerosol system, which is composed of particles, such as dust, sulfuric acid, and nitric acid floating in the air, is subject to relatively stable weather conditions [1,2,3]
The results showed that under the control of two high-pressure systems, mornings in this region were characterized by low wind, low temperature, and high relative humidity (RH) which corresponded to severe haze events
The mean sea level pressure (SLP) data used in the present study to classify the daily circulation type were derived from reanalyzed data from the National Centers for Environmental Prediction [33] with a horizontal resolution of 1◦ × 1◦ for the years 2007 to 2016 (September to February each year) and for the area ranging from 30◦ N–33◦ N, 118◦ E–123◦ E
Summary
Haze is a weather phenomenon that occurs when the aerosol system, which is composed of particles, such as dust, sulfuric acid, and nitric acid floating in the air, is subject to relatively stable weather conditions [1,2,3]. Used the subjective circulation classification method to study the relationship between haze and weather circulation in the Guanzhong region in China in winter and found that haze is related to certain circulation patterns. McGregor and Bamzelis [30] used K cluster analysis to classify weather circulation and studied the relationship between air quality and weather-scale systems in Birmingham, England. They found that continental high pressure caused haze events, whereas oceanic cyclone control did not have a strong effect. This work’s main goal was to analyze the relationship between multi-scale atmospheric circulation and severe haze events in autumn and winter in Shanghai, China.
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