Abstract
Abstract. An instrumented NASA P-3B aircraft was used for airborne sampling of trace gases in a plume that had emanated from a small forest understory fire in Georgia, USA. The plume was sampled at its origin to derive emission factors and followed ∼ 13.6 km downwind to observe chemical changes during the first hour of atmospheric aging. The P-3B payload included a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS), which measured non-methane organic gases (NMOGs) at unprecedented spatiotemporal resolution (10 m spatial/0.1 s temporal). Quantitative emission data are reported for CO2, CO, NO, NO2, HONO, NH3, and 16 NMOGs (formaldehyde, methanol, acetonitrile, propene, acetaldehyde, formic acid, acetone plus its isomer propanal, acetic acid plus its isomer glycolaldehyde, furan, isoprene plus isomeric pentadienes and cyclopentene, methyl vinyl ketone plus its isomers crotonaldehyde and methacrolein, methylglyoxal, hydroxy acetone plus its isomers methyl acetate and propionic acid, benzene, 2,3-butanedione, and 2-furfural) with molar emission ratios relative to CO larger than 1 ppbV ppmV−1. Formaldehyde, acetaldehyde, 2-furfural, and methanol dominated NMOG emissions. No NMOGs with more than 10 carbon atoms were observed at mixing ratios larger than 50 pptV ppmV−1 CO. Downwind plume chemistry was investigated using the observations and a 0-D photochemical box model simulation. The model was run on a nearly explicit chemical mechanism (MCM v3.3) and initialized with measured emission data. Ozone formation during the first hour of atmospheric aging was well captured by the model, with carbonyls (formaldehyde, acetaldehyde, 2,3-butanedione, methylglyoxal, 2-furfural) in addition to CO and CH4 being the main drivers of peroxy radical chemistry. The model also accurately reproduced the sequestration of NOx into peroxyacetyl nitrate (PAN) and the OH-initiated degradation of furan and 2-furfural at an average OH concentration of 7.45 ± 1.07 × 106 cm−3 in the plume. Formaldehyde, acetone/propanal, acetic acid/glycolaldehyde, and maleic acid/maleic anhydride (tentatively identified) were found to be the main NMOGs to increase during 1 h of atmospheric plume processing, with the model being unable to capture the observed increase. A mass balance analysis suggests that about 50 % of the aerosol mass formed in the downwind plume is organic in nature.
Highlights
Understanding and predicting the impacts of biomass burning emissions on air quality is a challenging but important task
The data demonstrate that the airborne PTRToF-MS instrument generates high-precision non-methane organic gases (NMOGs) data even for very localized emission sources
High-spatiotemporalresolution data were obtained for inorganic and organic trace gases, the latter being sampled for the first time at 1 Hz for instruments except PTR-ToF-MS (10 Hz) using a PTR-ToF-MS instrument
Summary
Understanding and predicting the impacts of biomass burning emissions on air quality is a challenging but important task. Fire emissions include a plethora of inorganic and organic species, both in the gas and the particulate phase, and many of them undergo rapid chemical transformations and phase changes after their release to the atmosphere (e.g., Simoneit, 2002) These processes are the focus of intense research efforts, both in the laboratory and in the field. Many airborne field studies have been undertaken to characterize emissions and evolution of gases and particles in the aging plume (e.g., Akagi et al, 2012, 2013; Yokelson et al, 2009) These studies have targeted emissions from medium and large-scale fires. Result in an oversimplification of the involved chemistry, which will yield erroneous model predictions
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