Online gas- and particle-phase measurements of organosulfates, organosulfonates and nitrooxy organosulfates in Beijing utilizing a FIGAERO ToF-CIMS
Authors: Le Breton Michael , Wang Yujue , Hallquist Åsa M. , Pathak Ravi Kant , Zheng Jing , Yang Yudong , Shang Dongjie , Glasius Marianne , Bannan Thomas J. , Liu Qianyun , Chan Chak K. , Percival Carl J. , Zhu Wenfei , Lou Shengrong , Topping David , Wang Yuchen , Yu Jianzhen , Lu Keding , Guo Song , Hu Min , Hallquist Mattias 
Published: July 2018

Abstract. A time-of-flight chemical ionization mass spectrometer (CIMS)
utilizing the Filter 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 are organo/nitrooxy organosulfates 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 variation in field observations
was confirmed by comparison to offline measurement techniques (orbitrap and
high-performance liquid chromatography, HPLC) using daily averages. The mean
total (of the 17 identified by CIMS) SCO particle mass concentration was
210 ± 110 ng m−3 and had a maximum of 540 ng m−3,
although it contributed to only 2 ± 1 % of the organic aerosol (OA).
The CIMS identified a persistent gas-phase presence of SCOs in the ambient
air, which was further supported by separate vapour-pressure measurements of
NP OS by a Knudsen Effusion Mass Spectrometer (KEMS). An increase in
relative humidity (RH) promoted partitioning of SCO to the particle phase,
whereas higher temperatures favoured higher gas-phase concentrations. Biogenic emissions contributed to only 19 % of total SCOs measured in this
study. Here, C10H16NSO7, a monoterpene-derived SCO,
represented the highest fraction (10 %) followed by an isoprene-derived
SCO. The anthropogenic SCOs with polycyclic aromatic hydrocarbon (PAH) and
aromatic precursors dominated the SCO mass loading (51 %) with
C11H11SO7, derived from methyl naphthalene oxidation,
contributing to 40 ng m−3 and 0.3 % of the OA mass. 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. In addition to typical anthropogenic and biogenic
precursors the biomass-burning precursor nitrophenol (NP) provided a
significant level of NP OS. It must be noted that the contribution analysis
here is only representative of the detected SCOs. There are likely to
be many more SCOs present which the CIMS has not identified. 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. Furthermore, the HSO4⋅H2SO4- cluster measured by the
CIMS was utilized as a qualitative marker for acidity and indicates that the
production of total SCOs is efficient in highly acidic aerosols with high
SO42- and organic content. This dependency becomes more complex
when observing individual SCOs due to variability of specific VOC precursors.