Different roles of water in secondary organic aerosol formation from toluene and isoprene

Abstract

Abstract. Roles of water in the formation of secondary organic aerosol (SOA) from the irradiations of toluene-NO 2 and isoprene-NO 2 were investigated in a smog chamber. Experimental results show that the yield of SOA from toluene almost doubled as relative humidity increased from 5 to 85 %, whereas the yield of SOA from isoprene under humid conditions decreased by 2.6 times as compared to that under dry conditions. The distinct difference of RH effects on SOA formation from toluene and isoprene is well explained with our experiments and model simulations. The increased SOA from humid toluene-NO 2 irradiations is mainly contributed by O-H-containing products such as polyalcohols formed from aqueous reactions. The major chemical components of SOA in isoprene-NO 2 irradiations are oligomers formed from the gas phase. SOA formation from isoprene-NO 2 irradiations is controlled by stable Criegee intermediates (SCIs) that are greatly influenced by water. As a result, high RH can obstruct the oligomerization reaction of SCIs to form SOA.

Effects of SO<sub>2</sub> on optical properties of secondary organic aerosol generated from photooxidation of toluene under different relative humidity

“…The addition of SO 2 caused an enhancement of total surface concentrations of the particles, probably because of the formation of new particles and/or acidic catalysed reactions, as implied in previous studies (Chu et al, 2016;Deng et al, 2017;Hallquist et al, 2009). Moreover, the S tot under wet conditions were higher than that under dry conditions as well, probably due to aqueous reactions of water soluble products, as indicated previously (Jia and Xu, 2018;Kamens et al, 2011;Hinks et al, 2018). 5…”

“…Lambe et al found that the conjugated double bonds could enhance the absorption in the UV-Vis light as well (Lambe et al, 2013). This phenomenon also is approved in previous reports (Jia and Xu, 2018;Faust et al, 2017;Liu et al, 2018b). 25…”

“…Multiphase reactions take an important place in SOA formation as well, as shown in previous studies. For example, Jia et al (Jia and Xu, 2018) have shown that the yield of toluene SOA almost doubled at relative humidity of 85 % compared to dry conditions (Hinks et al, 2018). Li et al found 5 multiphase reactions would enhance light scattering and radiative forcing of m-xylene SOA (Li et al, 2017c).…”

Secondary organic aerosol formation from photooxidation of furan: effects of NOx and humidity

“…The results were compared with the mass concentrations detected in humid mode, in which the humid air in the chamber was introduced into the SMPS with the sheath air set at 10 L min -1 . The ALW was calculated as the difference between the particle mass concentrations determined at dry and humid modes (Jia and Xu, 2018). On the basis of the recorded particle volume concentration and assumed particle density, a total suspended particulate (TSP in μg m -3 ) could be translated.…”

Secondary organic aerosol formation from photooxidation of furan: effects of NO<sub><i>x</i></sub> and humidity

“…Besides the mixed effect of NO x level on SOA formation, the RH can significantly alter the sizes of SOA particles, depending on their hygroscopicity (Varutbangkul et al, 2006), their gas-phase reactions involving water (Jonsson et al, 2006), and the aqueous chemistry occurring at their surfaces (Lim et al, 2010;Grgic et al, 2010). The photooxidation experiments with aromatic compounds, such as toluene (Edney et al, 2000;Cao and Jang, 2010;Faust et al, 2017;Hinks et al, 2018), benzene and ethylbenzene (Jia and Xu, 2014), m-xylene (Zhou et al, 2011), and 1,3,5-trimethylbenzene (Cocker et al, 2001) have been carried out previously to study the effect of RH on SOA formation.…”