| Autor: |
Crahan, Kathleen K.1 katie@atmos.washington.edu, Hegg, Dean1, Covert, David S.1, Jonsson, Haflidi2 |
| Předmět: |
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| Zdroj: |
Atmospheric Environment. Jul2004, Vol. 38 Issue 23, p3757-3764. 8p. |
| Abstrakt: |
Oxalic acid is the most abundant dicarboxylic acid found in the troposphere, yet there is still no scientific consensus concerning its origins or formation process. Recent studies have suggested mechanisms for its formation in cloud water from gaseous precursors. Comparison of the characteristics of oxalic acid and nss sulfate, a chemical with a known in-cloud formation pathway, provides some support for an aqueous formation mechanism for oxalic acid. Analysis of the filters collected from the CIRPAS Twin Otter aircraft during CARMA I, a field campaign designed to study the marine stratocumulus off the coast of Monterey, CA, by a five stage Micro-Orifice Impactor (MOI) revealed a peak in the concentration distribution at a diameter of 0.26–0.44 μm, similar to the size distribution found for nss sulfate and corresponding to the droplet mode in the aerosol size distribution. An air-equivalent average of 2.03±0.47 μg m-3 (standard error) of sulfate was observed in the collected marine cloud water, in excess to below-cloud concentrations by 1.16 μg m-3 on average. This suggests in-cloud production similar in concentration to previous field campaigns in coastal marine atmospheres. Oxalate was observed in the clouds at air-equivalent concentrations of 0.21±0.04 μg m-3, in excess to below-cloud concentrations by 0.14 μg m-3 and suggesting an in-cloud production as well. The tentative identification in cloud water of one of the intermediate species in the aqueous oxalate production mechanism lends further support to an in-cloud oxalate source. [Copyright &y& Elsevier] |
| Databáze: |
GreenFILE |
| Externí odkaz: |
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