Estimation of Secondary Organic Aerosol Formation During a Photochemical Smog Episode in Shanghai, China

Abstract

Secondary organic aerosols (SOA) are formed through diverse processes in the atmosphere, among which photochemical processing is one important pathway. SOA formation was studied based on one heavy photochemical smog episode in summer in Shanghai. During the pollution episode, ozone and organic carbon (OC) increased simultaneously with a strong positive correlation, which was complete opposite to the volatile organic compounds (VOCs) pattern but similar to that of VOC photochemical consumption. The OC evolution was explained well by a parameterization method based on the observation of OC and VOCs, and secondary OC (SOC) formation was derived, being comparable with the result based on elemental carbon (EC) tracer method. About 67% of SOC could be explained by the photochemical consumption of VOCs (mainly aromatics, ~93%) during the episode. The contribution of VOCs to SOC formation was also estimated from the available VOC emissions inventories, which was comparable with that based on VOCs observations in ambient. Some differences of VOC species contribution to SOC were found between the ambient observation‐based and the emission‐based results, and the contribution of C9 aromatics was underestimated in the emission inventory. This suggests that bias of speciation might exist in the current VOC emissions inventories. The present study highlights the importance of VOC oxidation for SOC formation in summer in Shanghai. More insights are needed to improve the accuracy of VOCs speciated emissions inventories.

Spatio-Temporal Variations of the PM2.5/PM10 Ratios and Its Application to Air Pollution Type Classification in China

“…Correspondingly, the dust particles caused by strong winds in spring in these areas are far less than that in those cities in Northwest and North China. In addition, the overall environmental humidity in the south is higher than that in the north, and the hygroscopic growth of new particles may also increase the proportion of PM 2.5 (Zhao et al, 2018a;Wang et al, 2020). Therefore, under the combined effect of multiple causes, it appears as a type of anthropogenic pollution in the cities of Sichuan Basin, central China, southern coast, and eastern China.…”

Investigation of the Acid-Mediated Photosensitized Reactions of Amphiphilic α-Keto Acids at the Air–Water Interface Using Field-Induced Droplet Ionization Mass Spectrometry

“…Among the large variety of amphiphilic molecules that are found in the atmosphere, α-keto acids have drawn great attention recently due to their ubiquity in nature as important metabolic products both from animals and plants. , Consequently, they are often found in atmospheric aerosols as a result of the direct release of living organisms and the oxidation of other organic molecules. − Photochemistry promotes the global formation of SOAs, , and the photochemistry of α-keto acids was investigated as early as 1963, but it was not linked to atmospheric relevance back then. Due to the existence of the extra π-conjugated carbonyl group compared to carboxylic acids, α-keto acids have higher absorption in the UVA region, making them more vulnerable to light in the atmosphere.…”

Removal of VOCs by Ozone: n-Alkane Oxidation under Mild Conditions

“…[1]. VOCs are considered major air pollutants because of their significant contribution to the formation of photochemical smog, tropospheric O 3 and secondary aerosols [2][3][4][5]. VOCs negatively affect human health because of their toxic, malodorous, mutagenic and carcinogenic nature [6].…”