Environmental Advances (Jul 2023)
Impact of nylon and teflon filter media on the sampling of inorganic aerosols over a high altitude site
Abstract
Water-soluble inorganic aerosols constitute major fraction of PM2.5 play an important role in the Earth-climate system and affect adversely on human health. However, their measurement accuracy highly vary depending on choice of filter media and denuder usage. In most of the cases, denuders are either not deployed or their use is partially limited to removal of certain gases. Therefore, to understand the impact of undenuded ambient sampling and filter media type on depositional loading of water-soluble inorganic aerosols; three (1 teflon and 2 nylon based) different pore-sized filter media sampling was carried at a high altitude location in Western Ghats during winter season. Results show gas-phase adsorption was higher on nylon than hydrophobic teflon membrane. Decreased pH and overall increased conductivity observed on nylon media suggested higher adsorption of acidic species. Nylon showed increasing ionic concentration and their order followed Mg2+Na+>Ca2+>K+. ISORROPIA-II derived high NH3 and Cl(g) found on nylon than the teflon. Poor correlation between X-ray Fluorescence (XRF) and Ion Chromatography (IC) derived crustal specie (Ca) showing off-set between both the results, however, were found positively correlated for secondary species (Cl−, NH4+, NO3+ and SO42−). Neutralization efficiency revealed secondary NH4+ as the main neutralizer for secondary NO3+ and SO42− on nylon whereas on teflon, Ca2+ was found to be the main neutralizing component. On comparing Na+ and Cl+ effects over neutralization, an extensive Cl(g) adsorption on nylon than on teflon suggested prevalence of non-seasalt sources. Concentration weighted trajectory analysis for nylon minus teflon indicated an excess semi-volatiles (Cl−, NO3− and NH4+) on nylon were mostly driven by the oxidation of precursory gases originating from local and nearby coastal cities, whereas non-refractory ultrafine mode aerosols were found from inland and from majorly polluted North Indian region.
