A New Approach for Quantifying the Total Amount of Organosulfur Compounds in Atmospheric Aerosols

Organosulfur compounds, crucial constituents of atmospheric aerosols, have adverse impacts on both air quality and climate change through their physicochemical properties. Their sources are diverse, including both primary emissions and secondary formation processes. Here, we establish a new approach for quantifying the total amount of organosulfur compounds by combining optimized high-temperature acidic hydrolysis (140 °C, 8 h, pH 2) and HNO3/H2O2 digestion (210 °C, 4 h) to convert organosulfur compounds into sulfate, followed by ion chromatography (IC) analysis. The method achieved high recoveries for different organic and inorganic sulfur standard mixtures. To further assess the method's reliability, standard particulate matter (NIST 1648a and 1649b) was analyzed, yielding a higher amount of total organosulfur compounds via water extraction and dissociation. Analysis of ambient aerosols also revealed that water-soluble organosulfur was dominant. The molecular composition of organosulfur compounds was subsequently determined by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The conversion factor, fOrgS, to estimate sulfur-containing organic matter (SOM) from organosulfur concentrations, was calculated to be around 9.35 in ambient samples. The methanol-soluble SOM in these samples ranged from 1.21 to 3.75 μg m-3, peaking in the afternoon and evening. However, as methanol-soluble organosulfur was not representative of the total organosulfur, the methanol-soluble SOM should be regarded as a lower bound for ambient SOM levels. This robust framework for total atmospheric organosulfur quantification provides a scientific basis for elucidating the sources and formation mechanisms of aerosols in ambient environments.