Mixing State of Size-Selected Submicrometer Particles During Photochemical and Combustion Events Measured with the Tandem System

摘要

A tandem differential mobility analyzer (TDMA) was applied to determine the mixing state of size-resolved submicrometer particles, in an urban area of Gwangju in Korea, when enhanced concentrations of particles were observed (e.g., photochemical and combustion events). The existence of a nonvolatile core was identified after removing volatile species with increasing temperature up to ~250°C. Data showed that in the combustion event, the accumulation mode particles (137-139 nm) increased significantly and they had a nonvolatile core coated with volatile species, while in the photochemical event, the nucleation mode (15-30 nm) particles enhanced and there was no such nonvolatile core (i.e., they were completely evaporated below 250° C). When hygroscopic growth factor (HGF) of the core particles was measured in the combustion event, their values were close to one, suggesting that they consist of nonvolatile and nonhygroscopic species like black carbon. In the photochemical event, the nucleation mode particles were completely evaporated at 250° C and had some volatile fractions at 100° C, unlike pure ammonium sulfate, and had C and S elements in their TEM/EDS data, suggesting that they have an internal mixture of sulfate and organics. Also, the HGF of the remaining particles after removing volatile species at 150° C increased, but not as much as expected for the case of complete evaporation of volatile species at this temperature. Data for evaporative behaviors of laboratory-generated aerosols (i.e., ammonium sulfate and succinic acid) suggest that evaporation of volatile species in a well-mixed mixture was delayed compared to those existing as single species.