Organic trace gas composition of the marine boundary layer over the northwest Indian Ocean in April 2000
- 標題
- Organic trace gas composition of the marine boundary layer over the northwest Indian Ocean in April 2000
- 作者
- C. Warneke, J.A. de Gouw
- 文件屬性
- 國外期刊
- 知識分類
- 基礎研究
- 出版年
- 2001
- 刊名
- Atmospheric Environment
- 關鍵字
- VOCs; NMHCs; Tropical marine boundary layer; DMS emissions; Variability–lifetime relationship; OH concentration
- 點閱數
- 3225
摘要
In April 2000 atmospheric trace gas measurements were performed on the western Indian Ocean on a cruise of the Dutch research vessel Pelagia from the Seychelles (5°S, 55°E) to Djibouti (12°N, 43°E). The measurements included analysis of dimethyl sulfide (DMS), acetone and acetonitrile every 40 s using PTR-MS (proton-transfer-reaction mass spectrometry) and gas chromatographic analyses of C2–C7 hydrocarbons in air samples taken during the cruise. The measurements took place at the end of the winter monsoon season and the sampled air masses came predominantly from the Southern Hemisphere, resulting in low concentrations of some long-lived hydrocarbons, halocarbons, acetone (350 pptv) and acetonitrile (120 pptv). On three consecutive days a diurnal cycle in DMS concentration was observed, which was used to estimate the emission of DMS (1.5±0.7×1013 molecules m−2 s−1) and the 24 h averaged concentration of hydroxyl (OH) radicals (1.4±0.7×106 molecules cm−3). A strongly increased DMS concentration was found at a location where upwelling of deeper ocean waters took place, coinciding with a marked decrease in acetone and acetonitrile. In the northwestern Indian Ocean a slight increase of some trace gases was noticed showing a small influence of pollution from Asia and from northeast Africa as indicated with back trajectory calculations. The air masses from Asia had elevated acetonitrile concentrations showing some influence of biomass burning as was also found during the 1999 Indian Ocean Experiment, whereas the air masses from northeast Africa seemed to have other sources of pollution.