Design and Testing of a Semi‐Continuous Measurement System for Ionic Species in PM2.5

Abstract

AbstractA semi‐continuous measurement system was constructed to investigate ionic species of fine particles less than 2.5 μm in aerodynamic diameter (PM2.5) in ambient air and at ca. 30 min time resolution. An intercomparison study was also performed with a typical integrated measurement technique (12‐h filter measurements) at the Gwangju Institute of Science and Technology (GIST), Gwangju, Korea. The system was composed of three main parts, i.e., a PM2.5 cyclone inlet connected to annular coating denuders, particle collection components and an ion chromatograph. Particle collection efficiencies in the range of 0.05 – 0.15 μm and 0.15 – 2.5 μm were 80 – 90 % and ca. 100 %, respectively, under the following conditions: distilled water (DW) flow rates, injected into the rectangular coil type air/liquid separator, over 0.23 mL min–1, with aerosol sampling and DW flow rates for steam generation of 2 L min–1 and 0.17 mL min–1, respectively. The limits of detection (3s of the blank value) of the system under the field experimental conditions were as follows: Na+ and NH4+: 0.20 μg m–3, K+: 0.25 μg m–3, Ca2+ and Mg2+: 0.50 μg m–3, and Cl–, NO3– and SO42–: 0.10 μg m–3. The intercomparison studies showed that the results of the semi‐continuous measurement system generally correlated with those of the 12‐h filter measurements for NH4+, SO42–, NO3– and Cl– (r = 0.82 ∼ 0.96, P < 0.0001, 95 % confidence limit). The correlation was best for SO42– (r = 0.96), but was relatively low for NO3– (r = 0.87) and Cl– (r = 0.82). The results indicated that the correlations between the two methods were mainly dependent upon the thermodynamic stability of the species in the fine particles and the sampling artifacts associated with the filter method.