Abstract
The long-path differential optical absorption spectroscopy (LP-DOAS) technique was deployed in Shanghai to continuously monitor ozone (O3), formaldehyde (HCHO), nitrogen dioxide (NO2), nitrous acid (HONO), and nitrate radical (NO3) mixing ratios from September 2019 to August 2020. Through a clustering method, four typical clusters of the O3 diurnal pattern were identified: high during both the daytime and nighttime (cluster 1), high during the nighttime but low during the daytime (cluster 2), low during both the daytime and nighttime (cluster 3), and low during the nighttime but high during the daytime (cluster 4). The drivers of O3 variation for the four clusters were investigated for the day- and nighttime. Ambient NO caused the O3 gap after midnight between clusters 1 and 2 and clusters 3 and 4. During the daytime, vigorous O3 generation (clusters 1 and 4) was found to accompany higher temperature, lower humidity, lower wind speed, and higher radiation. Moreover, O3 concentration correlated with HCHO for all clusters except for the low O3 cluster 3, while O3 correlated with HCHO/NOx, but anti-correlated with NOx for all clusters. The lower boundary layer height before midnight hindered O3 diffusion and accordingly determined the final O3 accumulation over the daily cycle for clusters 1 and 4. The interactions between the O3 diel profile and other atmospheric reactive components established that higher HONO before sunrise significantly promoted daytime O3 generation, while higher daytime O3 led to a higher nighttime NO3 level. This paper summarizes the interplays between day- and nighttime oxidants and oxidation products, particularly the cause and effect for daytime O3 generation from the perspective of nighttime atmospheric components.
Highlights
Introduction published maps and institutional affilIn the troposphere, the photochemical reactions of nitrogen oxides (NOx ) and volatile organic compounds (VOCs) act as major yield factors for ozone (O3 ) [1]
K-means clustering methodology response, we aimed to discard the time limit and classify the O3 pollution based only on was used to identify groups of O3 pollution according to diurnal patterns, which enabled the characteristics of the daily O3 variation
We investigated the impact of the period after midnight on the daytime as well as how it affected the period before midnight
Summary
The photochemical reactions of nitrogen oxides (NOx ) and volatile organic compounds (VOCs) act as major yield factors for ozone (O3 ) [1]. The strong oxidation potential of O3 renders it harmful for animals and plants [3], and a crucial driver for climate change [4] and ecosystem damage [5]. Severe O3 pollution episodes have repeatedly been reported over. In order to regulate and control tropospheric O3 formation, it is imperative to understand the drivers that integrate to cause changes in tropospheric O3 levels. In densely populated and economic zones such as eastern China, O3 pollution is severe because of the higher emissions of VOCs and NOx [9]
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