Precipitation chemistry and ozone and sulfate concentrations in the ocean atmosphere observed by multi-year cruising in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September
- 著者
- Aikawa M., Hiraki T., Mukai H.
- 雑誌名
- J. Atmos. Chem., 71(1), 65-78
- DOI
- 10.1007/s10874-014-9281-1
- 概要
-
A comprehensive study on the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere was carried out for the data sets in 1990’s. It is important to study the atmospheric situation over the past years as well as the latest, especially in the East Asian region where emission amount of anthropogenic air pollutants have increased year by year due to rapid economic growth. The survey was conducted for 5 years in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September in 1990’s. The purpose of the survey was to study and understand the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere comprehensively in one project. Rainfall over the ocean was insufficiently neutralized. Gas and aerosol over the ocean were mature, i.e., well-mixed, during the period of the transportation. The characteristic latitudinal dependence was observed in the tropospheric ozone concentration, namely, higher in the southern hemisphere and lower in the northern hemisphere (approximately 25 ppb in the 10–40°S region and 5–15 ppb in the 20–40°N region). On the other hand, high concentrations of tropospheric ozone of over 30 ppb were observed in the northern hemisphere, which was attributable to the long-range transportation. The TSP concentration was approximately under the level of 40 µgm−3 irrespectively of the latitude; in contrast, the nss-SO42− concentration showed a clear latitudinal dependence, i.e., higher in the northern hemisphere and lower in the southern hemisphere. The background levels of the nss-SO42− concentration were approximately 0.5 µgm−3 in the 10–40°S region and 2–3 µgm−3 and 4–5 µgm−3 in the 0–20°N and 20–40°N regions, respectively.
東アジアでは著しい経済発展が進んでおり、それに伴い、大気環境も変化していると考えられる。今回、1990年代の、海洋上（東アジアから西オセアニア）での大気の状況（大気中オゾン、大気エアロゾル、大気エアロゾル中の主成分の一つである非海塩性硫酸イオン及び降水）の調査結果を解析した。本報は、当時の調査結果が限られる1990代の、かつ元来調査結果が希少な海洋上の情報を明らかとした点に特徴がある。
調査は、1993〜1998年（1995年を除く）の8、9月に行われた。微小粒子状物質（PM2.5）の主な成分の一つでもある非海塩性硫酸イオンについては、発生源が多い北半球で高い濃度が観測され、緯度ごとの濃度分布の違いが明らかとなった。北緯20–40度での濃度レベル（4–5µg/m3）は、2000年代以降の日本国内で観測されるレベルと同程度であり、アジア大陸からの長距離輸送が示唆される結果であった。