Abstract:

Based on observational data of daily air quality index (AQI), hourly PM_2.5 concentration, and meteorological parameters in Tangshan from 2015 to 2017, we analyzed the characteristics of heavy air pollution and meteorological conditions for formation and dissipation of PM_2.5 pollution.The results show that the day number of heavy air pollution exhibits a decreasing trend from 2015 to 2017, with an annual mean value of 36 d.Heavy air pollution events occur most frequently during winter, followed by autumn.The primary air pollutant during heavy pollution events include PM_2.5, PM₁₀, and O₃, accounting for 87%, 6%, and 7%, respectively.The hourly PM_2.5 concentration has a positive correlation with relative humidity, total cloud fraction, and 24-h temperature change, and has a negative correlation with wind speed, air temperature, wind direction, and hourly precipitation.Such correlation is highest in winter, followed by autumn and spring.The relative humidity is higher than 50% for 90% of heavy PM_2.5 pollution events, and almost 98% in winter and autumn.The proportion of heavy PM_2.5 pollution events in the presence of wind speed larger than 4 m·s^-1 is 0.7%, and precipitation has a scavenging effect on air pollution to some degree.Pollution events tend to occur under conditions of increasing air temperature and humidity and negative pressure change.The average wind speed during the formation process of air pollution is 1.8 m·s^-1, with the dominant wind direction of the southwest, followed by southerly and westerly winds.The reduction of air temperature and humidity and positive pressure change favor the dissipation of air pollution, and the average wind speed reaches 3.1 m·s^-1 during the dissipation periods, predominantly controlled by easterly winds and then northeasterly and northerly winds.Wind speed larger than 3 m·s^-1 has a scavenging effect on air pollution, and northerly winds perform better than other wind direction despite lower wind speed.

Key words: PM_2.5, Heavy air pollution, Formation and dissipation, Meteorological conditions