Online gas- and particle-phase measurements of organosulfates, organosulfonates and nitrooxy organosulfates in Beijing utilizing a FIGAERO ToF-CIMS

A Time of Flight Chemical Ionisation Mass spectrometer (CIMS) utilizing the Fast Inlet for Gas and AEROsol (FIGAERO) was deployed at a regional site 40 km north west of Beijing and successfully identified and measured 17 sulfur containing organics (SCOs = organo/nitrooxyorgano sulfates and sulfonates) with biogenic and anthropogenic precursors. The SCOs were quantified using laboratory synthesized standards of lactic acid sulfate and nitrophenol organosulfate (NP OS). The mean total (of the 17 identified by CIMS) SCO particle mass concentration was 207 p 106 ng m −3 and had a maxima of 542 ng m −3 , although contributed to only 2 p 2.8 % of the organic aerosol (OA). SCO contribution to submicron mass (PM 1 ) indicates a dominant secondary production of SCO due to the low contribution of SCOs to PM 1 during periods of high mass loading. The CIMS identified a persistent gas phase presence of SCOs in the ambient air, which was further supported by post campaign vapour pressure measurements of NP OS. An increase in RH appeared to promote partitioning to the particle phase whereas higher temperatures favored higher gas phase concentrations. On average 12 % of the total SCOs were observed in the gas phase with C 10 H 16 NSO 7 having just 5 % and IEPOX OS having 44 % on average in the gas phase. Biogenic emissions contributed to only 19 % of total SCOs detected. C 10 H 16 NSO 7 , an alpha-pinene derived SCO, representing the highest fraction (10 %) followed by an isoprene-derived SCO. Anthropogenic SCOs with PAH and aromatic precursors dominated the SCO mass loading (51 % total SCOs) with C 11 H 11 SO 7 , derived from methyl napthalene oxidation, contributing to 40 ng m −3 and 0.3 % of the OA mass. Biomass burning was also identified as a potential anthropogenic and biogenic source of SCOs, based on nitrophenol (NP) and acetonitrile time series via secondary production of NP OS. Gas and particle phase measurements of glycolic acid suggest that partitioning towards the particle phase promotes glycolic acid sulfate production, contrary to the current formation mechanism suggested in the literature. Highly oxidised multifunctional organic compounds (HOMS) and RO 2 radical diurnal profiles, as measured by the iodide ToF-CIMS, are similar to that of total SCOs, supporting results that indicate HOMS are able to play a role in SCO production. Anthropogenic related SCOs correlated well with benzene, although their abundance depended highly on the photochemical age of the air mass, tracked using the ratio between pinonic acid and its oxidation product, acting as a qualitative photochemical clock. The HSO 4 .H 2 SO 4 − cluster measured by the CIMS was utilized as a qualitative marker for acidity and provides further evidence that the production rate of total SCOs is efficient in highly acidic aerosols with high SO 4 2− and organic content. This dependency becomes more complex when observing individual SCOs due to variability of specific VOC precursors.