Acidic gases (HCOOH, CH3COOH, HNO3, HCl, and SO2) and related aerosol species at a high mountain Alpine site (4360 m elevation) in Europe
Résumé
During a field campaign performed at 4360 m elevation in the French Alps in summer 2004, atmospheric levels of acidic gases (HCOOH, CH3COOH, HNO3, HCl, and SO2) and related aerosol species were investigated using mist chamber and denuder tube samplings. Sulfate aerosol levels greatly exceeded those of gaseous SO2. Conversely, chloride, nitrate and particularly monocarboxylates were much more present in the gas phase than in the aerosol phase. On a molar basis, formic and acetic acids are the most abundant acidic gases (∼14 nmol m−3 STP), followed by nitric acid (7 nmol m−3 STP), hydrochloric acid (1.7 nmol m−3 STP) and sulfur dioxide (0.8 nmol m−3 STP). These data gained in the free troposphere over Europe in summer are discussed and compared to those obtained during aircraft missions conducted over North America and the northwest Pacific near China. It is concluded that the concentrations of acidic gases and related aerosol species are quite similar in the free troposphere in summer over Europe and North America. Concentrations of sulfur and nitrogen species in the free troposphere are lower over Europe (and North America) than over the Pacific region located near China (a factor 5 and 2, respectively). Finally, measurements achieved in this study tend to indicate that secondary production is important for the atmospheric budget of carboxylic acids.
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