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| Titel |
Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy |
| VerfasserIn |
N. Zhang, X. Zhou, S. Bertman, D. Tang, M. Alaghmand, P. B. Shepson, M. A. Carroll |
| 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 ; 12, no. 17 ; Nr. 12, no. 17 (2012-09-13), S.8285-8296 |
| Datensatznummer |
250011447
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| Publikation (Nr.) |
 copernicus.org/acp-12-8285-2012.pdf |
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| Zusammenfassung |
| Systems have been developed and deployed at a North
Michigan forested site to measure ambient HONO and vertical HONO flux. The
modified HONO measurement technique is based on aqueous scrubbing of HONO
using a coil sampler, followed by azo dye derivatization and detection using
a long-path absorption photometer (LPAP). A Na2CO3-coated denuder
is used to generate "zero HONO" air for background correction. The lower
detection limit of the method, defined by 3 times of the standard deviation
of the signal, is 1 pptv for 1-min averages, with an overall uncertainty of
±(1 + 0.05 [HONO]) pptv. The HONO flux measurement technique has
been developed based on the relaxed eddy accumulation approach, deploying a
3-D sonic anemometer and two HONO measurement systems. The overall
uncertainty is estimated to be within ±(8 × 10−8 +
0.15 FHONO) mol m−2 h−1, with a 20-min averaged data point
per 30 min. Ambient HONO and vertical HONO flux were measured simultaneously
at the PROPHET site from 17 July to 7 August 2008. The forest canopy was
found to be a net HONO source, with a mean upward flux of 0.37 × 10−6 moles m−2 h−1. The HONO flux reached a maximal mean of
~0.7 × 10−6 moles m−2 h−1 around
solar noon, contributing a major fraction to the HONO source strength
required to sustain the observed ambient concentration of ~70 pptv.
There were no significant correlations between [NOx] and daytime
HONO flux and between JNO2 × [NO2] and HONO flux,
suggesting that NOx was not an important precursor responsible for HONO
daytime production on the forest canopy surface in this low-NOx rural
environment. Evidence supports the hypothesis that photolysis of HNO3
deposited on the forest canopy surface is a major daytime HONO source. |
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