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 HO(2) in the isoprene oxidation chain, thereby strongly enhancing the lifetime of gases in the forest boundary layer.
|Number of pages||19|
|Journal||Journal of Atmospheric Chemistry|
|Publication status||Published - Feb-2001|
- isoprene oxidation products
- tropical forest boundary layer
- box model
- VOLATILE ORGANIC-COMPOUNDS
- TROPOSPHERIC CHEMISTRY
- NONMETHANE HYDROCARBONS