Fatty Acid Surfactant Photochemistry Results in New Particle Formation

Abstract

Organic interfaces that exist at the sea surface microlayer or as surfactant coatings on cloud droplets are highly concentrated and chemically distinct from the underlying bulk or overlying gas phase. Therefore, they may be potentially unique locations for chemical or photochemical reactions. Recently, photochemical production of volatile organic compounds (VOCs) was reported at a nonanoic acid interface however, subsequent secondary organic aerosol (SOA) particle production was incapable of being observed. We investigated SOA particle formation due to photochemical reactions occurring at an air-water interface in presence of model saturated long chain fatty acid and alcohol surfactants, nonanoic acid and nonanol, respectively. Ozonolysis of the gas phase photochemical products in the dark or under continued UV irradiation both resulted in nucleation and growth of SOA particles. Irradiation of nonanol did not yield detectable VOC or SOA production. Organic carbon functionalities of the SOA were probed using X-ray microspectroscopy and compared with other laboratory generated and field collected particles. Carbon-carbon double bonds were identified in the condensed phase which survived ozonolysis during new particle formation and growth. The implications of photochemical processes occurring at organic coated surfaces are discussed in the context of marine SOA particle atmospheric fluxes.

Shipborne measurements of Antarctic submicron organic aerosols: an NMR perspective linking multiple sources and bioregions

“…The pattern of bands at 0.9, 1.3, 1.6, 2.2, 2.4, and 2.6 ppm follows the structure elucidated by Suzuki et al (2001) and is attributed to C 7 -C 9 aliphatic dicarboxylic acids and oxo-acids. This class of organic compounds, clearly characterizing the aliphatic composition of the ambient samples in the Weddell Sea area, could originate from degraded (oxidized) lipids (Kawamura et al, 1996), or from gas-to-particle conversion of carbonyls produced by the photochemical oxidation of lipids at the air-sea interface (Bernard et al, 2016;Alpert et al, 2017). Support for the lat-ter hypothesis (secondary formation) is given by the fact that the N-osmolytes (betaine, choline) present in the sea spray generated in the tanks were completely absent in the ambient sample.…”

“…In the paper by Liu et al (2018), Fouriertransform infrared (FTIR) spectroscopy was employed to probe the sources of particulate organic compounds at another coastal Antarctic site, and the results point to a contribution of marine polysaccharides transported in sea-spray aerosols. Finally, detailed organic speciation using offline analytical techniques with high sensitivity and selectivity suggest further contributions from marine proteinaceous material, terrestrial lipids, and secondary organic compounds (Bendle et al, 2007;Barbaro et al, 2015Barbaro et al, , 2017, but it is unclear how much the concentrations of compounds occurring at pg m −3 relate to that of bulk organic matter. We present here the organic characterization of Antarctic aerosol employing proton nuclear magnetic resonance ( 1 H-NMR) spectroscopy.…”

The opposing effect of butanol and butyric acid on the abundance of bromide and iodide at the aqueous solution–air interface

“…34,38 Recently, the fact that the ocean surface carries a layer consisting of a wealth of organic compounds deriving from marine biota has received a lot of attention. [39][40][41][42] Insight into the response of the halide ions especially also at mixed aqueous liquid surfaces to the presence of often surface active organics is crucial for understanding the chemistry of marine aerosols, brines associated with arctic sea ice and snow packs, which are more complex than just halide solutions, and for assessing the general implications of halogen chemistry.…”

Photochemical aging of atmospherically reactive organic compounds involving brown carbon at the air-aqueous interface

“…The unsaturated fatty acids also followed this mechanism during the processing of photosensitized oxidation. Past research has proposed the mechanism for the photosensitized degradation of a saturated fatty acid by the exited photosensitizer at the air-water interface (Tinel et al, 2016;Shrestha et al, 2018;Alpert et al, 2017). The radical produced by the initial hydrogen abstraction of the fatty acid can undergo two possible pathways.…”

“…When aerosols containing photosensitizers such as IC and HA were exposed to isoprene, limonene, α-pinene, β-pinene and toluene in the presence of UV light, there was significant SOA formation (Palacios et al, 2016). The gaseous products from interfacial photochemistry of organic film can act as precursors for SOA, while highly oxidized products are likely to be more water-soluble (Bruggemann et al, 2017;Alpert et al, 2017).…”