Measurement report: Collocated speciation and potential mechanisms of gaseous adsorption for integrated filter-based sampling and analysis of water-soluble organic molecular markers in the atmosphere

Abstract. To better understand the measurement uncertainties and sampling artifacts of particulate water-soluble organic molecular markers (WSOMMs), three quartz filters were stacked and installed in two collocated samplers (Sampler I and II) to simultaneously collect ambient WSOMMs. The paired top filters (Qf) loaded with PM2.5 were analyzed to determine the duplicate-derived uncertainty of particulate WSOMM concentrations. For several WSOMMs (e.g., levoglucosan) specifically associated with aerosol sources, the uncertainty was well below 20 %, which was commonly assumed in previous studies for the analysis of particulate WSOMMs. If the WSOMMs detected in the other two filters (Qb and Qbb) below Qf were caused by gaseous adsorption, the breakthrough value ([Qbb]/([Qb]+[Qbb])) can be used to estimate the sampling artifact of particulate WSOMMs due to gaseous adsorption on Qf. To understand the influence of acidic and alkaline conditions on the adsorption of gaseous WSOMMs or their precursors on quartz filters, the bottom filter (Qbb) of Sampler I was treated with (NH4)2SO4 or KOH on different sampling days. From the comparison of the measurement results between chemically treated and untreated Qbb samples, it was inferred that (NH4)2SO4 can increase the formation of isoprene secondary organic aerosol by reactive uptake of the oxidative intermediates; KOH can promote the adsorption of organic acids through neutralization reactions. Future studies are warranted to develop a suitable method for sampling gaseous WSOMMs using chemically treated adsorbents.