Collocated speciation of PM2.5 using tandem quartz filters in northern nanjing, China: Sampling artifacts and measurement uncertainty

In this study, collocated samples of particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5) were collected every sixth day on quartz filters (Qf) at a suburban site in northern Nanjing, China for one year. A backup quartz filter (Qb) was installed behind Qf to estimate positive artifacts. The analysis of gravimetric mass, water-soluble inorganic ions (WSIIs), total organic (OC) and elemental carbon (EC), water-soluble OC (WSOC), total nitrogen (WSTN) and organic nitrogen (WSON) were performed on both Qf and Qb. Due to the high mass loadings on Qf (17.9 ± 7.82 mg filter−1, 4.71–38.5 mg filter−1), the collocated precision of gravimetric mass and dominant species (NH4+, NO3−, SO42−, OC, and EC) is better than that from previous work. Except K+, EC, and WSON, all other target components were detected on Qb with average Qb/Qf ratios ranging from 3.02 ± 3.48–21.7 ± 22.4%. The final concentrations and uncertainties of PM2.5 components were determined based on duplicate Qf–Qb data. The results suggest that using an error fraction of 10% will underestimate the uncertainty of less concentrated species (e.g., Ca2+ and Mg2+) in PM2.5. Due to the evaporation loss of semi-volatile materials from the Qf, the Qf–Qb calculation would lead to an estimate of the lower limit for particulate NH4+, NO3−, and OC. Synchronized hourly data of PM2.5 mass and components were obtained at downtown Nanjing. The comparisons of gravimetric versus reconstructed PM2.5 and filter-based versus continuous measurements of PM2.5 components indicate that a substantial fraction of the unexplained gravimetric PM2.5 can be attributed to aerosol water. [Display omitted] •Collocated precision of PM2.5 components depends largely on filter loadings.•Besides OC adsorption, quartz filter sampling is also subject to surface reactions.•Assuming a constant error fraction of 10% is appropriate for PM2.5 major components.•Water content contributes a substantial fraction of the unexplained gravimetric PM2.5.