Collocated speciation of PM_(2.5) using tandem quartz filters in northern nanjing, China: Sampling artifacts and measurement uncertainty

摘要

In this study, collocated samples of particulate matter with aerodynamic diameter less than 2.5 mu m (PM2.5) were collected every sixth day on quartz filters (Q(f)) at a suburban site in northern Nanjing, China for one year. A backup quartz filter (Q(b)) was installed behind Q(f) 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 Q(f) and Q(b). Due to the high mass loadings on Q(f) (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 Q(b) with average Q(b)/Q(f) 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 Q(f)-Q(b) 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 Q(f), the Q(f)-Q(b) 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.