The concentration, trend and seasonal variation of metals in the atmosphere in 16 Japanese cities shown by the results of National Air Surveillance Network (NASN) from 1974 to 1996

In this study, the data from National Air Surveillance Network (NASN) for selected crustal elements (Al, Ca, Fe, Mn, Sc and Ti), anthropogenic elements (As, Cu, Cr, Ni, Pb, V and Zn) and a marine element (Na) in atmospheric particulate matter have been evaluated over Japan from 1974 to 1996. The NASN had 16 sampling stations, Nopporo, Sapporo, Nonotake, Sendai, Niigata, Tokyo, Kawasaki, Nagoya, Kyoto-Hachiman, Osaka, Amagasaki, Kurashiki, Matsue, Ube, Chikugo-Ogori and Ohmuta in Japan, at which aerosols were regularly collected every month and samples collected by low volume air sampler were analyzed by neutron activation analysis (NAA) and X-ray fluorescence (XRF). Results of trend analysis showed that the annual average concentrations of crustal and anthropogenic elements decreased significantly between 1974 and 1996. Furthermore, the concentrations of selected crustal and anthropogenic elements were higher between 1974 and 1979 than between 1980 and 1989. Crustal elements displayed high concentrations in the "Kosa" period (the dust season from March to May) and in winter (November and December) and low concentrations in summer (July and August). The ratios of elemental average concentrations in the Kosa period to those of summer were 2-5 times higher and those of winter relative to those of summer were 1.5-3 times higher for crustally derived elements. Particularly, concentration of Sc in Matsue was 8 times higher during the Kosa period than during summer time. Some of anthropogenic elements also showed high concentrations in the Kosa Season and low concentrations in summer. The ratios of elemental concentration in the Kosa period to those of summer and those of winter relative to summer were 2-4 times higher for some anthropogenically derived elements. Especially, the concentration of Zn in Chikugo-Ogori was 5.7 times higher during wintertime than during summertime. (C) 2000 Elsevier Science Ltd. All rights reserved.