Field comparison of methods for the measurement of gaseous and particulate contributors to acidic dry deposition

Abstract

A field study was conducted to compare methods for sampling and analysis of atmospheric constituents that are important contributors to acidic dry deposition. Comparisons are made of different measurements of ambient concentrations of gaseous HNO 3, NO 2, NH 3 and SO 2 and particulate NO 3 −, NH 4 + and SO 4 2−. Three multicomponent samplers were used: the Canadian filter pack (FP), the annular denuder system (ADS), and the transition flow reactor (TFR). A tunable diode laser absorption spectrometer (TDLAS) provided continuous reference measurements of NO 2 and HNO 3. Nitrogen dioxide was also monitored with continuous luminol-based chemiluminescence monitors and with passive sampling devices (PSDs). The study was designed to provide a database for statistical comparison of the various methods with emphasis on the multicomponent samplers under consideration for use in a national dry deposition trends monitoring network. The study was conducted at the EPA dry deposition station in Research Triangle Park, NC between 29 September and 12 October 1986. Daily averaging and/or sampling times were employed for the 13-day study; weekly samples were also collected, but results from these samples are not compared in this paper. ADS, TFR and FP results are in good agreement for measurements of the sum of particulate and gaseous NO 3 − concentrations and of total particulate SO 4 2−. ADS, FP, and TDLAS measurements of HNO 3 are in good agreement, but TDLAS results differ with and are substantially less than those from the TFR. TDLAS measurements of NO 2 are highly correlated with those of the TFR, but show mixed comparisons with results from the two luminol-based monitors and with results from the two sets of PSDs. TFR and FP measurements of particulate NH 4 + are in good agreement, but FP results exceed those of the ADS when volatilization losses of NH 4 + in the ADS are ignored. At the low ambient NH 3 concentrations, results of ADS, TFR, and FP show considerable variability but no statistically discernable differences. ADS results for measurements of SO 2 exceed those from both the TFR and FP. Non-quantitative recovery of SO 2 from various elements in the TFR and FP may account for this discrepancy.