Measurements of Hygroscopicity and Volatility of Atmospheric Ultrafine Particles during Ultrafine Particle Formation Events at Urban, Industrial, and Coastal Sites

Abstract

The tandem differential mobility analyzer (TDMA) technique was applied to determine the hygroscopicity and volatility of atmospheric ultrafine particles in three sites of urban Gwangiu, industrial Yeosu, and coastal Taean in South Korea. A database for the hygroscopicity and volatility of the known compositions and sizes of the laboratory-generated particles was first constructed for comparison with the measured proper-des of atmospheric ultrafine particles. Distinct differences in hygroscopicity and volatility of atmospheric ultrafine particles were found between a "photochemical event" and a "combustion event" as well as among different sites. At the Gwangju site, ultrafine particles in the "photochemical event" were determined to be more hygroscopic (growth factor (GF) = 1.05-1.33) than those in the "combustion event" (GF = 1.02-1.12), but their hygroscopicity was not as high as pure ammonium sulfate or sulfuric acid particles in the laboratory-generated database, suggesting they were internally mixed with less soluble species. Ultrafine particles in the "photochemical event" at the Yeosu site, having a variety of SO2, CO, and VOC emission sources, were more hygroscopic (GF = 1.34-1.60) and had a higher amount of volatile species (47-75%) than those observed at the Gwangju site. Ultrafine particle concentration at the Taean site increased during daylight hours with low tide, having a higher GF (1.34-1.80) than the Gwangju site and a lower amount of volatile species (17-34%) than the Yeosu site. Occasionally ultrafine particles were externally mixed according to their hygroscopicity and volatility, and TEM/EDS data showed that each type of particle had a distinct morphology and elemental composition.