The seasonal variations of the chemical components in airborne aerosols in a mountainous area were investigated. Field observations were made at Happo at an altitude of 1,850m in the central mountainous region of Japan. Airborne aerosol was collected for 12hours or 24hours from May 1998 to September 1999 and the chemical components (Na+, Mg2+, K+, Ca2+, NH4+, Cl-, SO42-, NO3- and oxalic acid) in the aerosol were measured. In addition, gaseous pollutants, such as ozone and SO2 were monitored simultaneously. The concentrations of Na+ were much higher from autumn to spring than those in summer. Cl- increased in winter and the seasonal variation differed from Na+. The concentrations of Mg2+, K+ and Ca2+, especially Ca2+ increased in spring. It suggests that the increase in this Ca2+ concentration is based on the influence of Kosa aerosol (yellow sand) transported from continental Asia. The concentrations of SO42- and oxalic acid produced by photochemical reaction increased from spring to summer, and NH4+ which is the neutralization ingredient of sulfuric acid showed also the same seasonal variation. The concentration ratios of Cl-/Na+ were quite low compared with that of sea water. This is based on Cl- loss reaction. There was almost no influence of sea salt in the mountainous area, because most of K+, Ca2+ and SO42- were non-sea salt. The sulfate conversion ratio, i.e., SO42- -[S]/(SO2-[S] + SO42--[S]), was as high as 0.8 in summer. In summer and winter, when the concentration of SO42- was high, total equivalent concentration of anions (Cl-, NO3- and SO42-) was much higher than that of cations (Na+, NH4+, K+, Mg2+ and Ca2+), which suggests that a portion of the SO42- existed in the form of acidic aerosols such as H3SO4 and NH4HSO4. It suggests that a part of sulfuric acid produced by the photochemical reaction is transported to the mountainous area without being neutralized by alkali substances, such as NH3.

This study investigated the distribution of organic matters in airborne aerosols. Field observations were made at Takasaki and Karuizawa, which are located along the route of the long-range transport of photochemical air pollution in summer, in two urban areas (Okaya and Nagano) in late autumn and early winter, in a rural area (Nakano) in late autumn and in a mountainous area (Happo) in autumn. Organic matter in airborne aerosol was collected on a quartz fiber filter using a high-volume air sampler for 3 days to a week. Organic compounds collected on the filter were extracted with dichlorometane and subsequently with methanol, and the extracts were subjected to GC/FID and GC/MS analyses. Pinonaldehyde, C17-C33 n-alkanes, C12-C26 fatty acids, dicarboxylic acids, phthalic acids, benzoic acid, lower molecular unresolved mixtures (LUCM) and higher molecular unresolved mixtures (HUCM) were detected in the airborne aerosols. The total concentrations of the analyzed matter accounted for approximately 20% of the organic carbon (OC) in any of the samples. Pinonaldehyde, dicarboxylic acids and phthalic acids, which are produced by photochemical reaction in the atmosphere, were more abundant in summer. Concentrations of long-chain fatty acids and UCM (LUCM + HUCM) increased in rural Nakano in late autumn, probably due to the vegetative burning of asparagus fields nearby. A large part of the analyzed matter was made up of anthropogenic compounds (n-alkanes, dicarboxylic acids, phthalic acids, benzoic acid and UCM), while biogenic ones (pinonaldehyde, n-alkanes and fatty acids) were minor contributors to the airborne aerosols. In the mountainous area, pinonaldehyde, oxalic acid and LUCM were considered to be produced by photochemical reactions during transport to Happo.