Enhanced secondary organic aerosol formation from the photo-oxidation of mixed anthropogenic volatile organic compounds

Abstract

Abstract. Motor vehicle exhaust is one of the important contribution sources of secondary organic aerosol (SOA) in urban areas. Long-chain alkanes and aromatic hydrocarbons are included in gaseous organic pollutants of vehicle emissions, representative for diesel and gasoline vehicles respectively. In this work, the SOA production from individual anthropogenic volatile organic compounds (AVOCs) (n-dodecane, 1,3,5-trimethylbenzene) and mixed AVOCs (n-dodecane + 1,3,5-trimethylbenzene) were studied with a large-scale outdoor smog chamber. Results showed that the SOA formation from the mixed AVOCs was enhanced compared to the predicted SOA mass concentration based on the SOA yield of individual AVOCs. According to the results of mass spectrometry analysis with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), interaction occurred between intermediate products from the two precursors, which could be the main reason for the enhanced SOA production from the mixed AVOCs reaction system. This study indicates that further studies on SOA chemistry from the mixed VOCs reaction system are needed, as the interactions between them and the effect on SOA formation can give us a further understanding of the SOA formed in the atmosphere.

Suppression of anthropogenic secondary organic aerosol formation by isoprene

“…On the other hand, the effect of VOC mixtures on SOA formation is not conclusive and may enhance or suppress SOA in different studies 23,[30][31][32][33] . For example, Li et al 31 found enhanced SOA formation by mixing two anthropogenic VOCs (n-dodecane and 1,3,5-trimethylbenzene) in the presence of NO x and sunlight, and their experiments were conducted in a large-scale outdoor chamber, which is close to the real atmospheric conditions.…”

“…On the other hand, the effect of VOC mixtures on SOA formation is not conclusive and may enhance or suppress SOA in different studies 23,[30][31][32][33] . For example, Li et al 31 found enhanced SOA formation by mixing two anthropogenic VOCs (n-dodecane and 1,3,5-trimethylbenzene) in the presence of NO x and sunlight, and their experiments were conducted in a large-scale outdoor chamber, which is close to the real atmospheric conditions. By contrast, Voliotis et al 32 found that the volatility of SOA from anthropogenic and biogenic VOC mixtures (o-cresol and α-pinene) was in between those measured in single-VOC systems, and their experimental conditions were representative of typical ambient daytime photochemistry with moderate relative humidity (50 ± 5%) and temperature (24 ± 2 °C).…”

“…However, there are still rather limited laboratory studies on the interactive effect of VOC mixtures from different sources-particularly the effects of biogenic VOC on anthropogenic SOA formation and composition-implying a significant knowledge gap regarding SOA formation chemistry. Given the fact that the real atmosphere is a complex mixture of thousands of organic and inorganic species from various sources 1,24,34 , an improved understanding of such interaction effects on SOA formation is much needed 18,31,35 , which consequently motivated the current work.…”