A comparison of new measurements of total monoterpene flux with improved measurements of speciated monoterpene flux

[摘要] Many monoterpenes have been identified in forest emissions using gaschromatography (GC). Until now, it has been impossible to determine whetherall monoterpenes are appropriately measured using GC techniques. We used aproton transfer reaction mass spectrometer (PTR-MS) coupled with the eddycovariance (EC) technique to measure mixing ratios and fluxes of totalmonoterpenes above a ponderosa pine plantation. We compared PTR-MS-ECresults with simultaneous measurements of eight speciated monoterpenes,β-pinene, α-pinene, 3-carene, d-limonene, β-phellandrene,α-terpinene, camphene, and terpinolene, made with anautomated, in situ gas chromatograph with flame ionization detectors(GC-FID), coupled to a relaxed eddy accumulation system (REA). Monoterpenemixing ratios and fluxes measured by PTR-MS averaged 30±2.3% and31±9.2% larger than by GC-FID, with larger mixing ratiodiscrepancies between the two techniques at night than during the day. Twounidentified peaks that correlated with β-pinene were resolved in thechromatograms and completely accounted for the daytime difference andreduced the nighttime mixing ratio difference to 20±2.9%.Measurements of total monoterpenes by PTR-MS-EC indicated that GC-FID-REAmeasured the common, longer-lived monoterpenes well, but that additionalterpenes were emitted from the ecosystem that represented an importantcontribution to the total mixing ratio above the forest at night.

[学科分类] 大气科学