Abstract
During the 2020 Chinese Spring Festival extended holidays and the COVID-19 period in Wuhan, the “quasi-zero emissions increase” occurred due to the human activities have a considerably lower impact on air quality. A new scientific question of concern: Why has high of O 3 and PM 2.5 still been observed? The comparative analysis of the influences of anomalous atmospheric circulation and weather conditions during this special period in 2019–2020 with those in the historical years can be useful. The results in the study were as follows: (1) Even during this “quasi-zero emissions increase” period, the concentrations of O 3 and PM 2.5 are higher than normal, with O 3 being significantly higher in Wuhan. Which is associated with a anomaly large-scale humid/warm water vapor transport in the Northern Hemisphere which is significantly different from that of the same period with historical more-haze years. (2) In this scenario, the large-scale humid/warm water vapor transport brings sustained high-humidity water vapor lifting conditions to north China. The daily cycling change of the sun's zenith angle to support the high-humidity and high-condensation condition are conducive to the elevation of high condensation ( f c ) and degree of super-saturation ( S ) going up to the peak of S >10%. Under the condition driven by high f c , it causes the power exponent law to be followed converting NO 2 to O 3 , thereby resulting in an increase in O 3 concentration. This additional contribution to O 3 concentration is as high as 37% than those from pure chemical process. (3) An objective quantitative reversal method for calculating the monthly threshold in f c is given based on the power exponential conversion law by the observed data. It can be prospectively applied to assess the feedback on the impact of pollution on urban climate. • Atmospheric Super-saturation is conducive to secondary conversion of O 3 precursors. • Water vapor conveyor belt maintains particle matter's humidification growth nearby. • Daily change of sun's zenith angle supports O 3 growth in power exponential transform.
Published Version
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