Abstract
Abstract. Secondary organic aerosol (SOA) has great impacts on air quality, climate change and human health. The composition and physicochemical properties of SOA differ greatly because they form under different atmospheric conditions and from various precursors as well as differing oxidation. In this work, photooxidation experiments of toluene were performed under four conditions (dry, dry with SO2, wet and wet with SO2) to investigate the effect of SO2 under different relative humidities on the composition and optical properties of SOA at wavelengths of 375 and 532 nm. According to our results, the increase in humidity enhances not only light absorption but also the scattering property of the SOA. Oligomers formed through multiphase reactions might be the reason for this phenomenon. Adding SO2 slightly lowers the real part of the complex refractive index, RI(n), of toluene-derived SOA (RI(n)dry,SO2<RI(n)dry, RI(n)wet,SO2<RI(n)wet), which might be a result of the partitioning of low-oxidation-state products. The imaginary part of the complex refractive index, RI(k), is enhanced under dry conditions with SO2 compared to that of only dry conditions, which might be due to acid-catalyzed aldol condensation reactions. Wet conditions with SO2 shows the combined effect of SO2 and humidity. The extinction properties of toluene-derived SOA under wet conditions with SO2 increased by approximately 30 % compared to that of toluene-derived SOA formed under dry conditions. Our results suggest that various atmospheric conditions will affect the composition and optical proprieties of SOA, which has significant implications for evaluating the impacts of SOA on the rapid formation of regional haze, global radiative balance and climate change.
Highlights
Secondary organic aerosol (SOA) accounts for a major fraction of the atmospheric fine particulate matters (PM2.5) and has significant impacts on air quality, climate change and human health (Seinfeld and Pandis, 2006; Jimenez et al, 2009; Hallquist et al, 2009; Huang et al, 2014)
The size distributions, number concentrations and mass concentrations of the SOA were determined by a scanning mobility particle sizer (SMPS), which consisted of an electrostatic classifier (EC; TSI 3080), a differential mobility analyzer (DMA; TSI 3081) and a condensation particle counter (CPC; TSI 3776)
The effect of SO2 under different humidities on the optical properties of SOA photooxidized by toluene was investigated in this study
Summary
Secondary organic aerosol (SOA) accounts for a major fraction of the atmospheric fine particulate matters (PM2.5) and has significant impacts on air quality, climate change and human health (Seinfeld and Pandis, 2006; Jimenez et al, 2009; Hallquist et al, 2009; Huang et al, 2014). Previous studies have mostly focused on the enhancement of SOA yields introduced by the presence of SO2 for isoprene, α-pinene and anthropogenic precursors (Santiago et al, 2012; Kleindienst et al, 2006; Liggio and Li, 2013) They revealed that an enhancing effect of SOA yields is because of the acidic aerosol products of SO2 and the formation of new particles. More research is needed on the role of SO2 in the subsequent optical properties of SOA formed from various VOCs. Field studies have shown that haze events were often accompanied by high relative humidity (RH) (Sun et al, 2016a, b), and organic aerosols were mostly liquid (Shiraiwa et al, 2017; Liu et al, 2017). The data in the current study will be highly useful for the simulation of models and field observations performed under various pollution conditions
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
