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

Abstract

<p><strong>Abstract.</strong> Secondary organic aerosol (SOA) have great impacts on air quality, climate change and human health. The composition and physicochemical properties of SOA differ a lot for they originated under different atmospheric conditions and from various precursors and oxidations. In this work, photooxidation experiments of toluene were performed under four conditions (dry, dry with SO<sub>2</sub>, wet, and wet with SO<sub>2</sub>) to investigate the effect of SO<sub>2</sub> under different relative humidity on the composition and optical properties of SOA at the wavelength of 375 nm and 532 nm. According to our results, the increase of humidity enhances not only light absorption, but also scattering property of SOA. Highly conjugated oligomers formed through multiphase reaction might be the reasons of this phenomenon. Adding SO<sub>2</sub> slightly lower the real part of complex refractive index (n) of SOA: n<sub>dry, SO2</sub> < n<sub>dry</sub>, n<sub>wet, SO2</sub> < n<sub>wet</sub>, which might be a result of the partitioning of low oxidation state products, such as alcohols, esters, and so on. The imaginary part of complex refractive index (k) are enhanced under condition dry with SO2 compared to condition dry might because of the enhancement of charge transfer complexes, a great contributor to ultraviolet and visible light absorption. Condition wet with SO<sub>2</sub> shows the combined effect of SO<sub>2</sub> and humidity condition. The extinction properties of toluene-derived SOA under condition wet and SO<sub>2</sub> are increased about 30 % compared to condition dry. Our results suggest that various atmospheric conditions will affect the composition and optical proprieties of SOA, which have significant implications for evaluating the impacts of SOA on the rapid-formation of regional haze, global radiative balance and climate change.</p>

Molecular Absorption and Evolution Mechanisms of PM2.5Brown Carbon Revealed by Electrospray Ionization Fourier Transform–Ion Cyclotron Resonance Mass Spectrometry During a Severe Winter Pollution Episode in Xi'an, China

“…CHNOS molecules with S/C less than 0.04 were the dominant contributors to b abs (CHNOS), whereas those with S/C higher than 0.04 (molecules with two or more sulfate functional groups) tended to have limited contributions to BrC absorption. Compared with N‐containing functional groups, the addition of S‐containing functional groups tended to weaken Mb abs of CHNOS, which is consistent with results of quantum chemical calculations (Nakayama et al, 2015) and smog chamber experiments (Zhang et al, 2019). Such a phenomenon is probably because sulfate‐containing groups are not chromophoric and rather have a hypochromic effect on the molecule (Moise et al, 2015; Nguyen et al, 2012).…”

A large-scale outdoor atmospheric simulation smog chamber for studying atmospheric photochemical processes: Characterization and preliminary application

“…A series of photochemical simulation experiments of hydrocarbons and NOx were designed and conducted according to the atmospheric conditions in Lanzhou and Beijing (Zhang and Li, 1998). Then a serious environmental issues were studied based on the smog chambers constructed with various size in the past decades, including the mechanism of photochemical reaction (Liu et al, 2017;Wang et al, 2014;Wu et al, 2007), ozone and SOA formation (Li et al, 2018a;Ma et al, 2018;Wang et al, 2015), biomass burning reactions (Zhang et al, 2011), the photochemical process of the gasoline and diesel (Chen et al, 2019a;Chen et al, 2019b;Kamens et al, 2011), physicochemical properties of SOA formed under various conditions (Li et al, 2017a;Li et al, 2020;Li et al, 2018b;Peng et al, 2018;Zhang et al, 2020), et al However, most of the chambers constructed in China were indoor smog chambers, establishment large-scale outdoor smog chambers in China was limited. In order to study the atmospheric pollution process close to China's actual atmospheric environment, it was necessary to build a large outdoor smog chamber in China.…”

Effects of OH radical and SO2 concentrations on photochemical reactions of mixed anthropogenic organic gases

“…Laboratory studies demonstrated that the presence of SO 2 could enhance the SOA formation from anthropogenic and biogenic precursors, e.g. monoterpenes, isoprene, aromatics (Liggio and Li, 2013;Santiago et al, 2012;Kleindienst et al, 2006;Zhang et al, 2020;Yang et al, 2020;Liu et al, 2019). In addition, the presence of SO 2 could affect the light scattering and absorption properties of formed SOA (Zhang et al, 2020;Jaoui et al, 2008;Nakayama et al, 2015Nakayama et al, , 2018.…”

“…monoterpenes, isoprene, aromatics (Liggio and Li, 2013;Santiago et al, 2012;Kleindienst et al, 2006;Zhang et al, 2020;Yang et al, 2020;Liu et al, 2019). In addition, the presence of SO 2 could affect the light scattering and absorption properties of formed SOA (Zhang et al, 2020;Jaoui et al, 2008;Nakayama et al, 2015Nakayama et al, , 2018. It should be noted that most of the previous studies focused on the effect of SO 2 on the particle formation from a single precursor.…”