Tracing the biogenic secondary organic aerosol markers in rain, snow and hail

The molecular characterization of secondary organic aerosol (SOA) is based mainly on LC-MS analyses of particulate matter (PM) samples collected with aerosol samplers. Several studies have analyzed atmospheric waters, including rain and cloud water, for the presence of SOA components, however, no separation techniques were used making identification of the individual components in these complex mixtures impossible. We have applied our improved UHPLC-HR-MS methodology to analyze atmospheric precipitates (hailstone, rain and snow), as well as SOA collected with high-volume samplers. We achieved sensitivity levels and separation efficiencies that were sufficient for molecular-level identification of individual compounds. Tracing commonly known SOA markers such as organosulfates (OS), C₄-C₆ dicarboxylic acids and terpenoic acids revealed that the chromatographic profiles for both atmospheric precipitate and PM samples were very similar, with both giving similar component ratios, especially for OS. We also demonstrated that SOA markers can be detected directly from raw rain samples. Our results show that LC-MS techniques are suitable for the convenient analysis of atmospheric precipitates containing SOA markers at the molecular level. It complements traditional SOA analyses and provides additional sampling opportunities which will no doubt allow for better elucidation of chemical transformations of volatile organic compounds in the atmosphere.