Abstract
In this study, a separation and quantification method for ammonium sulfate in ambient PM2.5 was developed. Aqueous solutions of four major ammonium salts in PM2.5, i.e., ammonium sulfate, ammonium hydrogen sulfate, ammonium nitrate and ammonium chloride, were added to a quartz fiber filter and dried. Next, the filter was subjected to heat treatment to separate the ammonium sulfate from the other ammonium salts. By heating the filter to 110℃ for 30 min, ammonium nitrate and ammonium chloride volatilized, and only ammonium sulfate and ammonium hydrogen sulfate remained on the filter. Furthermore, by heating the filter to 150℃ for 30 min, the ammonium sulfate splits into ammonium hydrogen sulfate and ammonia, so half of the NH4 in the ammonium sulfate volatilized. The other sulfate salts that were estimated to be present in PM2.5, i.e., sodium sulfate, potassium sulfate and calcium sulfate, did not decrease by the heat treatments at 110℃ and 150℃. Hence, after the heat treatments, the ammonium ion, which decreased by heating at 150℃ compared to heating at 110℃, was confirmed to originate from the ammonium sulfate. Thus the concentration of ammonium sulfate in the PM2.5 was estimated from the decreased ammonium ion concentration and the ratio of the formula weight. Using this developed method, the concentration of ammonium sulfate in ambient PM2.5 was estimated to be 1.8 μg/m3 in January and 2.5 μg/m3 in February, 2018.
