Journal
JOURNAL OF ATMOSPHERIC CHEMISTRY
Volume 38, Issue 2, Pages 167-185Publisher
SPRINGER
DOI: 10.1023/A:1006326802432
Keywords
isoprene; isoprene oxidation products; tropical forest boundary layer; box model; methylvinylketone; methacrolein
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Airborne measurements of volatile organic compounds (VOC) were performed over the tropical rainforest in Surinam (0-12 km altitude, 2 degrees -7 degrees N, 54 degrees -58 degrees W) using the proton transfer reaction mass spectrometry (PTR-MS) technique, which allows online monitoring of compounds like isoprene, its oxidation products methyl vinyl ketone, methacrolein, tentatively identified hydroxy-isoprene-hydroperoxides, and several other organic compounds. Isoprene volume mixing ratios (VMR) varied from below the detection limit at the highest altitudes to about 7 nmol/mol in the planetary boundary layer shortly before sunset. Correlations between isoprene and its product compounds were made for different times of day and altitudes, with the isoprene-hydroperoxides showing the highest correlation. Model calculated mixing ratios of the isoprene oxidation products using a detailed hydrocarbon oxidation mechanism, as well as the intercomparison measurement with air samples collected during the flights in canisters and later analysed with a GC-FID, showed good agreement with the PTR-MS measurements, in particular at the higher mixing ratios. Low OH concentrations in the range of 1-3 x 10(5) molecules cm(-3) averaged over 24 hours were calculated due to loss of OH and HO2 in the isoprene oxidation chain, thereby strongly enhancing the lifetime of gases in the forest boundary layer.
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