Development of Semicontinuous Measurement System of Ionic Species in PM2.5

Abstract

A new method to semicontinuously determine PM2.5 ionic species with a short time resolution is described in detail. In this system, a particle collection section (mixing part, particle collection chamber, and air/liquid separator) was developed. A Y-type connector was used to mix steam and an air sample. The particle collection chamber was constructed in the form of a helix coil and was cooled by a water circulation system. Particle size growth occurred due to the high relative humidity and water absorbed particles were efficiently collected in it. Liquid samples were drained out with a short residence time (0.08-0.1 s). The air/liquid separator was also newly designed to operate efficiently when the flow rate of the air sample was 16.7 L min(-1). For better performance, the system was optimized for particle collection efficiency with various types of test aerosols such as (NH4)(2)SO4, NaCl, NH4HSO4, and NH4NO3. The particle collection efficiencies were almost 100% at different concentration levels in the range over 500 run in diameter but 50-90% in the range of 50-500 nm under the following experimental conditions: 15 coil turns, a water flow rate for steam generation of 0.65 mL min(-1), and ail air sample flow rate of 16.7 L min(-1). Finally, for atmospheric applications, chemical compositions of PM2.5 were determined with a time resolution of 20 min oil January 11-24, 2006 in Seoul, Korea, and the chemical characteristics of PM2.5 ions were investigated.