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| Titel |
Sources contributing to background surface ozone in the US Intermountain West |
| VerfasserIn |
L. Zhang, D. J. Jacob, X. Yue, N. V. Downey, D. A. Wood, D. Blewitt |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 11 ; Nr. 14, no. 11 (2014-06-02), S.5295-5309 |
| Datensatznummer |
250118760
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| Publikation (Nr.) |
 copernicus.org/acp-14-5295-2014.pdf |
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| Zusammenfassung |
| We quantify the sources contributing to background surface ozone
concentrations in the US Intermountain West by using the GEOS-Chem chemical
transport model with 1 / 2° × 2 / 3° horizontal
resolution to interpret the Clean Air Status and Trends Network (CASTNet) ozone monitoring data for 2006–2008. We
isolate contributions from lightning, wildfires, the stratosphere, and
California pollution. Lightning emissions are constrained by observations and
wildfire emissions are estimated from daily fire reports. We find that
lightning increases mean surface ozone in summer by 10 ppbv in the
Intermountain West, with moderate variability. Wildfire plumes generate
high-ozone events in excess of 80 ppbv in GEOS-Chem, but CASTNet ozone
observations in the Intermountain West show no enhancements during these
events nor do they show evidence of regional fire influence. Models may
overestimate ozone production in fresh fire plumes because of inadequate
chemistry and grid-scale resolution. The highest ozone concentrations
observed in the Intermountain West (> 75 ppbv) in spring are
associated with stratospheric intrusions. The model captures the timing of
these intrusions but not their magnitude, reflecting numerical diffusion
intrinsic to Eulerian models. This can be corrected statistically through a
relationship between model bias and the model-diagnosed magnitude of
stratospheric influence; with this correction, models may still be useful to
forecast and interpret high-ozone events from stratospheric intrusions. We
show that discrepancy between models in diagnosing stratospheric influence is
due in part to differences in definition, i.e., whether stratospheric ozone
is diagnosed as produced in the stratosphere (GEOS-Chem definition) or as
transported from above the tropopause. The latter definition can double the
diagnosed stratospheric influence in surface air by labeling as
"stratospheric" any ozone produced in the troposphere and temporarily
transported to the stratosphere. California pollution influence in the
Intermountain West frequently exceeds 10 ppbv but is generally not
correlated with the highest ozone events. |
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