Diurnal variation of ionic aerosol species and water-soluble gas concentrations at a high-elevation site in the Japanese Alps

Size-separated atmospheric aerosol particles, acidic gases, and ammonia were collected during the daytime and nighttime at Murododaira (36.6 degreesN, 137.6 degreesE, 2450 m above sea level), Mount Tateyama, Japan in early winter. 'Non-sea-salt (nss) SO42- in fine fractions (< 2.1 mum in diameter) was the most dominant ionic constituent and occupied 44% on average of the ionic mass concentration other than H-. Concentration levels of aerosol ions and water-soluble gases were higher during the day and lower at night. Concentrations of the nighttime aerosol particles and gases (except for SO2) were similar to free-tropospheric background levels at various sites of northern midlatitudes in the literature, suggesting that nighttime data at Murododaira were representative of free-tropospheric conditions. High concentration levels of SO2 at Murododaira. were close to those over the northwest Pacific Rim region during the winter season. Molar ratios of nssSO(4)(2-)/SO2 can be explained by the transport time from the Asian continent, suggesting that a significant source of fine nssSO(4)(2-) aerosols at Murododaira in early winter could be due to the oxidation of anthropogenic SO2 derived from the Asian continent. The equivalent ratios of nssSO(4)(2-) to NH4+ in fine particles were close to 0.5 under westerly wind conditions, suggesting the existence of half-neutralized sulfate on average.