Insights into the Formation and Evolution of Individual Compounds in the Particulate Phase during Aromatic Photo-Oxidation

Abstract

1Secondary organic aerosol (SOA) is well known to have adverse effects on air quality and 2 human health. However, the dynamic mechanisms occurring during SOA formation and 3 evolution are poorly understood. The time resolved SOA composition formed during the 4 photo-oxidation of three aromatic compounds, methyl chavicol, toluene and 4-methyl 5 catechol, were investigated at the European Photo-reactor. SOA was collected using a particle 6 into liquid sampler and analysed offline using state-of-the-art mass spectrometry to produce 7 temporal profiles of individual photo-oxidation products. In the photo-oxidation of methyl 8 chavicol, 70 individual compounds were characterised and three distinctive temporal profile 9 shapes were observed. The calculated mass fraction (Ci,aer/COA) of the individual SOA 10 compounds showed either a linear trend (increasing/decreasing) or exponential decay with 11 time. Substituted nitrophenols showed an exponential decay, with the nitro-group on the 12 aromatic ring found to control the formation and loss of these species in the aerosol phase. 13Nitrophenols from both methyl chavicol and toluene photo-oxidation experiments showed a 14 strong relationship with the NO2/NO (ppbv/ppbv) ratio and were observed during initial SOA 15 growth. The location of the nitrophenol aromatic substitutions was found to be critically 16 important, with the nitrophenol in the photo-oxidation of 4-methyl catechol not partitioning 17 into the aerosol phase until irradiation had stopped; highlighting the importance of studying 18 SOA formation and evolution at a molecular level.

Rate constant and secondary organic aerosol formation from the gas-phase reaction of eugenol with hydroxyl radicals

“…The relative low volatility of N-containing products could reasonably contribute to SOA formation (Duporté et al, 2016;. In addition, a higher NO 2 /NO ratio favors the formation of nitro-substituted products, which are potentially involved in NPF and SOA growth (Pereira et al, 2015). Ng et al (2007a) also indicated that NO x could be beneficial to SOA formation for sesquiterpenes due to the formation of low-volatility organic nitrates and the isomerization of large alkoxy radicals, resulting in less volatile products.…”

Observations of fine particulate nitrated phenols in four sites in northern China: concentrations, source apportionment, and secondary formation

“…Wang et al: Observations of fine particulate nitrated phenols aerosols (SOAs; Pereira et al, 2015). Via photo-oxidation and aqueous-phase reactions, nitrated phenols could alter the tropospheric photochemistry and influence SOA formation, thus affecting regional air quality and atmospheric visibility (Mohr et al, 2013;Laskin et al, 2015;Chow et al, 2016;Yuan et al, 2016).…”

“…Via photo-oxidation and aqueous-phase reactions, nitrated phenols could alter the tropospheric photochemistry and influence SOA formation, thus affecting regional air quality and atmospheric visibility (Mohr et al, 2013;Laskin et al, 2015;Chow et al, 2016;Yuan et al, 2016). In addition, nitrated phenols are hazardous to plants, animals, aquatic life, and humans (Natangelo et al, 1999;Schüssler and Nitschke, 2001;Harrison et al, 2005a;Ganranoo et al, 2010). The significant roles of nitrated phenols in the atmosphere and their adverse effects on living things have triggered the need to understand their pollution characteristics and their origins.…”

Replies to reviewer 1's comments

“…In this work, C 8 H 7 NO 4 and C 9 H 9 NO 4 from BB emissions are more stable and are supposed to have a phenyl cyanate structure. Among the four NAC formulas with MW > 200 Da identified in this work (Table 2), C 10 H 11 NO 4 was also observed as 5-methoxy-4-nitro-2-(prop-2-en-1-yl)phenol in SOA from reactions of methyl chavicol and NO x (Pereira et al, 2015), which cannot be assigned to the C 10 H 11 NO 4 from BB emissions in this work. Compared to the NACs in aromatic VOCs and NO x SOA (Iinuma et al, 2010;Lin et al, 2015;Xie et al, 2017a;Pereira et al, 2015), the structures of NACs from BB in this work were characterized by methoxy and cyanate groups.…”