Abstract
Abstract. The Focused Isoprene eXperiment at the California Institute of Technology (FIXCIT) was a collaborative atmospheric chamber campaign that occurred during January 2014. FIXCIT is the laboratory component of a synergistic field and laboratory effort aimed toward (1) better understanding the chemical details behind ambient observations relevant to the southeastern United States, (2) advancing the knowledge of atmospheric oxidation mechanisms of important biogenic hydrocarbons, and (3) characterizing the behavior of field instrumentation using authentic standards. Approximately 20 principal scientists from 14 academic and government institutions performed parallel measurements at a forested site in Alabama and at the atmospheric chambers at Caltech. During the 4 week campaign period, a series of chamber experiments was conducted to investigate the dark- and photo-induced oxidation of isoprene, α-pinene, methacrolein, pinonaldehyde, acylperoxy nitrates, isoprene hydroxy nitrates (ISOPN), isoprene hydroxy hydroperoxides (ISOPOOH), and isoprene epoxydiols (IEPOX) in a highly controlled and atmospherically relevant manner. Pinonaldehyde and isomer-specific standards of ISOPN, ISOPOOH, and IEPOX were synthesized and contributed by campaign participants, which enabled explicit exploration into the oxidation mechanisms and instrument responses for these important atmospheric compounds. The present overview describes the goals, experimental design, instrumental techniques, and preliminary observations from the campaign. This work provides context for forthcoming publications affiliated with the FIXCIT campaign. Insights from FIXCIT are anticipated to aid significantly in interpretation of field data and the revision of mechanisms currently implemented in regional and global atmospheric models.
Highlights
We provide a brief background of the oxidation of biogenic hydrocarbons, which includes “state-of-thescience” knowledge, to motivate the study
Data analysis is ongoing, the goals of the FIXCIT campaign appear to have been met during the campaign period
The insights gained from experimental observations under well-controlled laboratory conditions have already proved valuable for understanding ambient observations from Southern Oxidant and Aerosol Study (SOAS)
Summary
1.1 BackgroundBiogenically produced isoprenoids (hydrocarbons comprised of C5H8 units) have global emission rates into the atmosphere surpassing those of anthropogenic hydrocarbons and methane (Guenther et al, 1995, 2012). The biogenic carbon emission flux is dominated by isoprene (C5H8) and monoterpenes (C10H16), which account for approximately 50 and 30 % of the OH reactivity over land, respectively (Fuentes et al, 2000). It has been suggested that the atmospheric oxidation of isoprene, in particular, can buffer the oxidative capacity of forested regions by maintaining levels of the hydroxyl radical (OH) under lower nitric oxide (NO) conditions (Lelieveld et al, 2008). The accurate representation of detailed chemistry for isoprene and monoterpene is necessary for meaningful simulations of atmospheric HOx (OH + HO2), NOx (NO + NO2), surface ozone (O3), trace gas lifetimes, and SOA
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