An automated and semi-continuous method for the analysis of water-soluble constituents in PM2.5

An automated and semi-continuousmethod formeasuringwater-soluble constituents in PM2.5 was developed. The system consists of a multi-tube diffusion scrubber (MTDS), a low temperature particle impactor (LTPI), an inertial air/liquid separator, and two ion chromatography systems. The MTDS acts as an interfering gas removal system and also as a humidifier for growing particles. Since the MTDS operates at 40 °C, the loss of volatile compounds and hydrological conversion of nitrogen oxides to nitrite were not of significant concern. The condensation of water vapor, dissolution of soluble constituents, and capture of insoluble particles occurred in the LTPI. The condensed liquid containing the dissolved species and the insoluble particleswas separated fromthe airflowusing an inertial air/liquid separator. The analysis of cations and anions in the effluent liquid was performed using two ion chromatography systems. The collection efficiency, including the inlet loss, of the systemwas 96.6±7.1% at an air flowrate of 1.0 SLPM. The limits of detection ranged from12 to 57 ng/m3 for major ionic constituents without any pre-concentration procedure. Thismethod was tested in the fieldand the average data capturewas over 90%,demonstratingthe reliability of the system.