Characterization of Atmospheric PM(2.5)Inorganic Aerosols Using the Semi-Continuous PPWD-PILS-IC System and the ISORROPIA-II

Abstract

A semi-continuous monitoring system, a parallel plate wet denuder and particle into liquid sampler coupled with ion chromatography (PPWD-PILS-IC), was used to measure the hourly precursor gases and water-soluble inorganic ions in ambient particles smaller than 2.5 mu m in diameter (PM2.5) for investigating the thermodynamic equilibrium of aerosols using the ISORROPIA-II thermodynamic equilibrium model. The 24-h average PPWD-PILS-IC data showed very good agreement with the daily data of the manual 5 L/min porous-metal denuder sampler with R(2)ranging from 0.88 to 0.98 for inorganic ions (NH4+, Na+, K+, NO3-, SO42-, and Cl-) and 0.89 to 0.98 for precursor gases (NH3, HNO3, HONO, and SO2) and slopes ranging from 0.94 to 1.17 for ions and 0.87 to 0.95 for gases, respectively. In addition, the predicted ISORROPIA-II results were in good agreement with the hourly observed data of the PPWD-PILS-IC system for SO42-(R-2= 0.99 and slope = 1.0) and NH3(R-2= 0.97 and slope = 1.02). The correlation of the predicted results and observed data was further improved for NH(4)(+)and NO(3)(-)with the slope increasing from 0.90 to 0.96 and 0.95 to 1.09, respectively when the HNO(2)and NO(2)(-)were included in the total nitrate concentration (TN = [NO3-] + [HNO3] + [HONO] + [NO2-]). The predicted HNO(3)data were comparable to the sum of the observed [HNO3] and [HONO] indicating that HONO played an important role in the thermodynamic equilibrium of ambient PM(2.5)aerosols but has not been considered in the ISORROPIA-II thermodynamic equilibrium model.