Chemical Transformation of α-Pinene derived Organosulfate via Heterogeneous OH Oxidation: Implications for Sources and Environmental Fates of Atmospheric Organosulfates

Abstract

Abstract. Organosulfur compounds are found to be ubiquitous in atmospheric aerosols — a majority of which are expected to be organosulfates (OSs). Given the atmospheric abundance of OSs, and their potential to form a variety of reaction products upon ageing, it is imperative to study the transformation kinetics and chemistry of OSs to better elucidate their atmospheric fates and impacts. In this work, we investigated the chemical transformation of an α-pinene derived organosulfate (C10H17O5SNa, αpOS-249) through heterogeneous OH oxidation at a relative humidity of 50 % in an oxidation flow reactor (OFR). The aerosol-phase reaction products were characterized using the high-performance liquid chromatography-electrospray ionization-high resolution mass spectrometry and the ion chromatography. By monitoring the decay rates of αpOS-249, the effective heterogeneous OH reaction rate was measured to be (6.72 ± 0.55) × 10−13 cm3 molecule−1 s−1. This infers an atmospheric lifetime of about two weeks at an average OH concentration of 1.5 × 106 molecules cm–3. Product analysis shows that OH oxidation of αpOS-249 can yield more oxygenated OSs having a nominal mass-to-charge ratio (m/z) at 247 (C10H15O5S−), 263 (C10H15O6S−), 265 (C10H17O6S−), 277 (C10H13O7S−), 279 (C10H15O7S−), and 281 (C10H17O7S−). The formation of fragmentation products, including both small OSs (C < 10) and inorganic sulfates, is found to be insignificant. These observations suggest that functionalization reactions are likely the dominant processes and that multigenerational oxidation possibly leads to formation of products with one or two hydroxyl and carbonyl functional groups adding to αpOS-249. Furthermore, all product ions except m/z = 277 have been detected in laboratory generated α-pinene derived secondary organic aerosols as well as in atmospheric aerosols. Our results reveal that OSs freshly formed from the photochemical oxidation of α-pinene could react further to form OSs commonly detected in atmospheric aerosols through heterogeneous OH oxidation. Overall, this study provides more insights into the sources, transformation, and fate of atmospheric OSs.

Chemical transformation of a long-chain alkyl organosulfate via heterogeneous OH oxidation: a case study of sodium dodecyl sulfate

“…The experimental setup and procedures have been described elsewhere. 57,68 In brief, SDS was dissolved in ultra-pure deionized water. Aqueous aerosols were then generated by atomizing the solution through a constant output atomizer (without passing through a diffusion dryer) and subsequently mixing with nitrogen (N 2 ), oxygen (O 2 ), and ozone (O 3 ) before being introduced into the OFR.…”

“…The number of carbon atoms in alkyl OSs might therefore represent a factor limiting the inorganic sulfate yield upon heterogeneous OH oxidation, which is also in agreement with the detected low sulfate yield from a-pinene OS. 57 Our results might imply that our fundamental understanding of the chemical evolution principles of structurally different OSs is incomplete; therefore, further research in the related area is required.…”

“…Importantly, several unidentified OS can be explained, in respect of formation mechanisms, by heterogeneous OH oxidation of OS. 54,57 Regarding the formation of other products, Xu et al 56 reported the significant molar yield of inorganic sulfates from methyl OS, defined as the numbers of moles of bisulfate (HSO 4 -) and sulfate (SO 4 -) ions generated per mole of parent OS reacted, to be mounted up to (62 ± 18) % upon heterogeneous OH oxidation. From these findings, it is reasonable to hypothesize that a portion of OS may not be as atmospherically stable species as previously presumed.…”

“…[51][52][53] Heterogeneous oxidation by the hydroxyl radical (OH) is an efficient way to chemically transform OSs. [54][55][56][57] Literature studies utilized oxidation ow reactors to investigate OS species such as short-chain alkyl OSs (methyl sulfate (methyl OS, CH 3 SO 4 À ) and ethyl sulfate (ethyl OS, C 2 H 5 SO 4 À )), 55,56 monoterpene-derived OSs (a-pinene OS, C 10 H 17 O 5 S À ), 57 and isoprene-epoxydiol-derived OSs (2-methyltetrol sulfates and 3methyltetrol sulfates (2-/3-methyltetrol OS, C 5 H 11 SO 7 À )). 58 Their results demonstrated that all these OSs can be oxidized by OH efficiently with a chemical lifetime ranging from 10 to 15 days.…”

“…Importantly, several unidentied OSs can be explained, with respect to formation mechanisms, by heterogeneous OH oxidation of OSs. 54,57 Regarding the formation of other products, Xu et al 56 reported a signicant molar yield of inorganic sulfates from methyl OS, dened as the number of moles of bisulfate (HSO 4 À ) and sulfate (SO 4…”