Overestimation of Ammonium and its Relation to Ion Balance in Fine Dust (PM2.5) According to the Denuder Installation

Abstract

When collecting air samples for analyzing the ionic components of fine dust, a (+) error may occur because gaseous precursors react with each other on the filter surface to form particles. To remove NO2, SO2, HNO3, HNO2, and NH3, which may cause these errors, a denuder must be installed in front of the sampling port. However, with the extensive use of sequential samplers that automatically replaces filters once every 24 h, the use of denuders is decreasing. In this study, the effect of denuder installation was analyzed by operating a sampler simultaneously with and without a denuder on 279 samples collected from Gwangjin, Seoul. It was confirmed that the NH4 + concentration of the sampler equipped with a denuder was 13.4%~26.9% less than that of the sampler without the denuder when the fine particle concentration was less than 30 μg/m. Further, less nitrate and sulfate were detected when the denuder was installed. However, their levels were not as low as that of NH4 . This is likely because nitrate and sulfate are collected in a form bound to water soluble organic carbon particles and then eluted to add anions to lower the ion balance. In addition, when the denuder was not installed, the ion balance value was higher than that with the denuder installed, which was attributed to the partial neutralization of negative ions by gaseous ammonia. Therefore, to determine whether an error occurs during the experiment, the ion balance should be carefully maintained.