The Tropical Forest and Fire Emissions Experiment: method evaluation of volatile organic compound emissions measured by PTR-MS, FTIR, and GC from tropical biomass burning

摘要

Volatile Organic Compound (VOC) emissions from fires in tropical forestfuels were quantified using Proton-Transfer-Reaction Mass Spectrometry(PTRMS), Fourier Transform Infrared Spectroscopy (FTIR) and gaschromatography (GC) coupled to PTRMS (GC-PTR-MS). We investigated VOCemissions from 19 controlled laboratory fires at the USFS (United StatesForest Service) Fire Sciences Laboratory and 16 fires during an intensiveairborne field campaign during the peak of the burning season in Brazil in2004. The VOC emissions were dominated by oxygenated VOCs (OVOC) (OVOC/NMHC~4:1, NMHC: non-methane hydrocarbons) The specificity of the PTR-MSinstrument, which measures the mass to charge ratio of VOCs ionized byH₃O+ ions, was validated by gas chromatography and byintercomparing in-situ measurements with those obtained from an open pathFTIR instrument. Emission ratios for methyl vinyl ketone, methacrolein,crotonaldehyde, acrylonitrile and pyrrole were measured in the field for thefirst time. Our measurements show a higher contribution of OVOCs thanpreviously assumed for modeling purposes. Comparison of fresh (<15min) and aged (>1 h–1 d) smoke suggests altered emission ratiosdue to gas phase chemistry for acetone but not for acetaldehyde andmethanol. Emission ratios for numerous, important, reactive VOCs withrespect to acetonitrile (a biomass burning tracer) are presented.