Abstract
The reaction of gas-phase SO2 with unsaturated carbon-carbon double bonds forms organosulfates at the surface of the aerosol. Previous studies have focused on the reaction products and not the fate of organic films in the atmosphere. Neutron reflectometry was used to study the interaction of gas-phase SO2 at the air-water interface with organic material extracted from atmospheric particulate matter and pure proxy chemicals to determine whether the reaction of organic films with SO2 removes the film and if a product film is formed. Films formed from atmospheric aerosol collected in urban and woodland environments typically produced a layer of approximately 0.6 nm thickness, whereas a thick (>40 nm) film was formed by the woodsmoke sample. Fitting of this thicker woodsmoke film suggested a three-layered structure at the interface that has been interpreted to be consistent with a surfactant-rich layer next to the air-water interface, a mid-layer rich in polyaromatic hydrocarbons (PAH), and topped with a more aliphatic region. The multilayer structure of atmospheric extracted material at the air-water interface is potentially an exciting result that requires further study. Gas-phase SO2 was confirmed to react with pure insoluble surfactant molecules at the air-water interface that contained carbon-carbon double bonds (oleic acid) and did not react with a similar saturated surfactant (stearic acid). No reaction was observed during the interaction of SO2 and atmospheric material extracted from urban and woodland environments, and no material appeared to be removed from the interface; however, films made from woodsmoke-extracted material did appear to be altered by SO2 but there was no significant loss of material. In addition, the gas-phase ozone mixing ratios in the neutron blockhouse, which have historically been of some concern for reactions with organics, were found to be of the order 15 ppb, with no evidence of additional production in the neutron beam-path. Owing to a lack of substantial removal of material from real atmospheric extracted films, SO2 is not considered atmospherically significant for the removal of organic films from the air-water interface.
| Original language | English |
|---|---|
| Journal | Environmental Science: Atmospheres |
| DOIs | |
| State | Accepted/In press - 2024 |
| Externally published | Yes |
Funding
The authors would like to acknowledge the work by the support network at the ISIS neutron and muon source for providing the beam time and making this experiment possible by maintaining the facility, providing engineering works for our sample environment and providing constant support throughout the experiments RB2210230 and RB2310464. Particular acknowledgement is extended to Andy Church, Tom Charleston, Sarah Langham, James Taylor, Ludmilla Mee and Maura Martellini. Acknowledgements are made to NERC (NE/T00732X/1) for funding this work. Further acknowledgements are extended to the Earth Science support teams at Royal Holloway, university of London, whose engineering of the filter holders made the extraction of atmospheric particulate material possible. The authors would like to thank Forestry Research, UK, for allowing us to sample woodland particulate material from the Alice Holt plantation. SHJ is grateful to the German Research Foundation (DFG) for funding (JO 1849/1-1). Lastly, thanks is given to William Bloss of the University of Birmingham for the generous loan of the ozone monitoring equipment.
| Funders | Funder number |
|---|---|
| Natural Environment Research Council | NE/T00732X/1 |
| Natural Environment Research Council | |
| Deutsche Forschungsgemeinschaft | JO 1849/1-1 |
| Deutsche Forschungsgemeinschaft |
