01 Dec 2021

01 Dec 2021

Review status: this preprint is currently under review for the journal ACP.

Secondary Organic Aerosols from OH Oxidation of Cyclic Volatile Methyl Siloxanes as an Important Si Source in the Atmosphere

Chong Han1,2, Hongxing Yang2, Kun Li1,3, Patrick Lee1, John Liggio1, Amy Leithead1, and Shao-Meng Li4 Chong Han et al.
  • 1Air Quality Research Division, Environment and Climate Change Canada, Toronto, Ontario M3H 5T4, Canada
  • 2School of Metallurgy, Northeastern University, Shenyang, 110819, China
  • 3Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen 5232, Switzerland
  • 4State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China 100871

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.

Chong Han et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on Han et al.', Anonymous Referee #1, 21 Dec 2021
  • RC2: 'Comment on acp-2021-965', Anonymous Referee #2, 22 Dec 2021
  • RC3: 'Comment on acp-2021-965', Anonymous Referee #3, 12 Jan 2022

Chong Han et al.


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Short summary
We presented yields and compositions of Si-containing SOA generated from the reaction of cVMS (D3-D6) with OH radicals. NOx played negative roles on cVMS SOA formation, while ammonium sulfate seeds enhanced D3-D5 SOA yields at short photochemical ages under high-NOx conditions. The aerosol mass spectra confirmed that the components of cVMS SOA significantly relied on OH exposure. A global cVMS-derived SOA source strength was estimated to understand SOA formation potentials of cVMS.