Assessment of the aerosol water content in urban atmospheric particles by the hygroscopic growth measurements in Sapporo, Japan

摘要

Aerosol water content (AWC) of urban aerosol particles was investigated based on the hygroscopic growth measurements for 100 and 200 nm particles using a hygroscopicity tandem differential mobility analyzer in Sapporo, Japan in July 2006. In most of the humidogram measurements, presence of less and more hygroscopic modes was evident from the different dependence on relative humidity (RH). The volume of liquid water normalized by that of dry particle (V_[W](RH)/V_[dry]) was estimated from the HTDMA data for 100 and 200 nm particles. The RH dependence of V_[W](RH)/V_[dry] was well represented by a fitted curve with a hygroscopicity parameter K_[eff]. The K_[eff] values for 200 nm particles were in general higher than those for 100 nm particles, indicating a higher hygroscopicity of 200 nm particles. Based on the K_[eff] values, the volume mixing ratios of water-soluble inorganic compounds (ammonium sulfate equivalent) were estimated to be on average 31% and 45% for 100 and 200 nm particles, respectively. The diurnal variation Of K_[eff], with relatively higher values in the noontime and nighttime and lower values in the morning and evening hours, was observed for both particle sizes. The V_[W](RH)/V_[dry] values under ambient RH conditions were estimated from K_[eff] to range from 0.05 to 2.32 and 0.06 to 2.43 for 100 nm and 200 nm particles, respectively. The degree of correlation between K_[eff] and V_[W](RH)/V_[dry] at ambient RH suggests a significant contribution of the variation Of K_[eff] to atmospheric AWC in Sapporo.