Abstract
Cyclic volatile methyl siloxanes (cVMS) are active ingredients in widely used consumer products, which can volatilize into the atmosphere, thus attracting much attention due to their potential environmental risks. While in the atmosphere the cVMS undergo oxidation yielding both gaseous and particulate products. The aerosol yields and compositions from the OH oxidation of four cVMS (D3-D6) were determined under low and high-NOx conditions in an oxidation flow reactor. The aerosol yields progressively increased from D3 to D6, consistent with the volatilities and molecule weights of these cVMS. NOx can restrict the formation of SOA, leading to lower SOA yields under high-NOx conditions than under low-NOx conditions, with a yield decrease between 0.05–0.30 depending on the cVMS. Ammonium sulfate seeds exhibited minor impacts on SOA yields under low-NOx conditions, but significantly increased the SOA yields in the oxidation of D3-D5 at short photochemical ages under high-NOx conditions. The mass spectra of the SOA showed a dependence of its chemical compositions on OH exposure. At high exposures, equivalent to photochemical ages of > 6 days in the atmosphere, D4-D6 SOA mainly consisted of CxHy and CxHyOzSin under low-NOx conditions, whereas they primarily contained NmOz, CxHy, CxHyO1, CxHyO>1 and CxHyOzSin under high-NOx conditions. Using the yield data from the present study and reported cVMS annual production, a global cVMS-derived SOA source strength is estimated to be 0.16 Tg yr−1, distributed over major urban centers.
Highlights
Secondary organic aerosols (SOA), which contribute 50-85% to the mass of atmospheric organic aerosols (OA) (Glasius and Goldstein, 2016), are mainly formed via the partitioning of low volatility products from oxidation of volatile organic compounds (VOCs), semi- and intermediate volatile organic compounds(S/IVOCs) (Riipinen et al, 2012)
The yields and compositions of SOA generated from the photooxidation of four Cyclic volatile methyl siloxanes (cVMS) (D3-D6) with OH
Radicals were investigated using an oxidation flow reactor. cVMS SOA yields exhibited an overall increasing trend with photochemical age (PA), and their values gradually increased with cVMS from D3 to D6
Summary
Secondary organic aerosols (SOA), which contribute 50-85% to the mass of atmospheric organic aerosols (OA) (Glasius and Goldstein, 2016), are mainly formed via the partitioning of low volatility products from oxidation of volatile organic compounds (VOCs), semi- and intermediate volatile organic compounds(S/IVOCs) (Riipinen et al, 2012). As one type of anthropogenic VOC and potential SOA precursors, cyclic volatile methyl siloxanes (cVMS). Are widely used in industrial applications and personal care products (Genualdi et al, 2011; Krogseth et al., 2013a). Studies of cVMS in the environment have focused on investigating health and environmental impacts due to their potential persistence, bioaccumulation and toxicity (Guo et al, 2019; Liu et al, 2018; Farasani and Darbre, 2017; Xu et al, 2019; Kim et al, 2018; Coggon et al, 2018). The legislative actions notwithstanding, knowledge of environmental behavior of cVMS remains surprisingly scarce as compared to their applications and economic significance (Rücker and Kümmerer, 2015).
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