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| Titel |
Glyoxal as a tracer of VOC oxidation chemistry: Comparison of measurements with model results for Blodgett Forest, California |
| VerfasserIn |
Andrew Huisman, Annmarie Carlton, Frank Keutsch |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038209
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| Zusammenfassung |
| We present a study investigating Volatile Organic Compound (VOC) oxidation chemistry in
the context of regional ozone (O3) production during the BEARPEX 2007 and 2009
campaigns at Blodgett Forest Research Station (BFRS) in the Sierra Nevada mountains, CA.
Measurements are compared with results from a regional model (US EPA CMAQ) and a zero
dimensional (0-D) box model based on the Master Chemical Mechanism (MCM). We use
glyoxal (CHOCHO) and formaldehyde (HCHO) as tracers for generalized oxidation
processes and employ ratios of compounds (e.g. CHOCHO / HCHO, CHOCHO / MPAN) to
study plume evolution as doing so attenuates the influence of meteorology. One of the goals
of this study is to investigate the utility of glyoxal as a tracer of VOC oxidation chemistry for
measurement/model comparisons, for which formaldehyde has served in the past. In this
context, we investigate the discrepancies between models and measurements, and the
degree to which these can be attributed to the representation of glyoxal chemistry
(e.g. yields) or whether these discrepancies reflect VOC-HOx-NOx oxidation more
generally, which has implications for ozone and secondary organic aerosol formation.
Model results from CMAQ and the 0-D box model substantially overestimate the absolute
measured concentration of CHOCHO at BFRS, and the CMAQ model also shows
poor agreement with the diurnal profile. The 0-D box model also overestimates
CHOCHO in data taken at the Caltech Indoor Air Chambers, suggesting that 2nd- and/or
higher-generation yields of CHOCHO from isoprene are substantially overestimated
in the MCM. 0-D model results that use attenuated 2nd- and higher-generation
production of CHOCHO from isoprene show enhanced agreement with chamber results.
We will present model results of the 0-D Box Model from BFRS employing these reduced
yields that show improved agreement with measurements and also compare these results with
the other models. We also present results obtained with two modifications of the CMAQ
model; one with scaled glyoxal yields, and another in which overall VOC-HOx-NOx
oxidation chemistry was adjusted in addition to the glyoxal yields. We will discuss the degree
to which scaling glyoxal yields resolves the model-measurement disparities compared to
factors such as HOx and NOx that affect general VOC oxidation chemistry. The latter factors
affect CMAQ photochemistry more significantly, and might impact CMAQ O3 predictions,
which are currently excellent for BFRS. |
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