Abstract
Unlike the heavy haze situations in previous years, the emergence of a water vapor conveyor belt flowing through North China is an important factor in the foggy-haze event during the 48-h snowfall in Beijing and its surroundings, which disrupted the customary pollution snow removal atmospheric purification. ①In the spring of 2020, during a period of negative emissions increment and weak human activity impact, a special interaction between the high humidity content of large-scale continuous water vapor transmission and the weather-scale daily cycling radiation cycle change (due to daily change of sun's zenith angle), as well as the atmospheric microphysical process, provided rare meteorological conditions for the superposition-compound growth of PM 2.5 and O 3 pollution. The water vapor conveyor belt, through enhanced transmission of easterly wind momentum, induced a high value super-saturation signal ( S ) and condensation rate ( f c ), resulting in 48 consecutive hours of snow in Beijing, but was also conducive to fine particulates, including precursor emissions, through a microphysical humidification process, which became synchronized. ②The weather-scale process impact refers to the cloud height rise in the daytime and decrease at night. Due to the daily fluctuations in cloud height, the concentration of O 3 followed a coordinated daily cycle. During the day, when the sun's zenith angle going on the top, the PM 2.5 and O 3 superposition composite effects occur. Therefore, even during a negative emission period, PM 2.5 and O 3 superposition-composite serious pollution events occur as usual, rather than the expected possible atmospheric cleaning through snow. • Special meteorological condition is resulting in composite pollution of PM 2.5 & O 3 • Interaction between water vapor transport & microphysical condensation is the key • Daily cycling change of solar radiation supports composite pollution of O 3 & PM 2.5
Published Version
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