Emissions and ambient distributions of Biogenic Volatile Organic Compounds (BVOC) in a ponderosa pine ecosystem: interpretation of PTR-MS mass spectra

摘要

Two proton-transfer-reaction mass spectrometry systems were deployed at theBio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, HO,Organics and Nitrogen-Southern Rocky Mountain 2008 field campaign(BEACHON-SRM08; July to September, 2008) at the Manitou Forest Observatoryin a ponderosa pine woodland near Woodland Park, Colorado USA. The twoPTR-MS systems simultaneously measured BVOC emissions and ambientdistributions of their oxidation products. Here, we present mass spectralanalysis in a wide range of masses ( 40 to 210) to assess ourunderstanding of BVOC emissions and their photochemical processing inside ofthe forest canopy. The biogenic terpenoids, 2-methyl-3-butene-2-ol (MBO,50.2%) and several monoterpenes (MT, 33.5%) were identified as thedominant BVOC emissions from a transmission corrected mass spectrum(PTR-MS), averaged over the daytime (11 a.m. to 3 p.m., local time) of threedays. To assess contributions of oxidation products of local BVOC, wecalculate an oxidation product spectrum with the OH- and ozone-initiatedoxidation product distribution mass spectra of two major BVOC emissions atthe ecosystem (MBO and -pinene) that were observed from laboratoryoxidation experiments. The majority (~76%) of the total signal inthe transmission corrected PTR-MS spectra could be explained by identifiedcompounds. The remainder are attributed to oxidation products of BVOCemitted from nearby ecosystems and transported to the site, and oxidationproducts of unidentified BVOC emitted from the ponderosa pine ecosystem.