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| Titel |
NO3 radical measurements in a polluted marine environment: links to ozone formation |
| VerfasserIn |
R. McLaren, P. Wojtal, D. Majonis, J. McCourt, J. D. Halla, J. Brook |
| 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 ; 10, no. 9 ; Nr. 10, no. 9 (2010-05-05), S.4187-4206 |
| Datensatznummer |
250008422
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| Publikation (Nr.) |
 copernicus.org/acp-10-4187-2010.pdf |
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| Zusammenfassung |
| Nighttime chemistry in polluted regions is dominated by the nitrate radical
(NO3) including its direct reaction with natural and anthropogenic
hydrocarbons, its reaction with NO2 to form N2O5, and
subsequent reactions of N2O5 to form HNO3 and chlorine
containing photolabile species. We report nighttime measurements of
NO3, NO2, and O3, in the polluted marine boundary layer
southwest of Vancouver, BC during a three week study in the summer of 2005. The
concentration of N2O5 was calculated using the well known
equilibrium, NO3+NO2↔N2O5. Median overnight
mixing ratios of NO3, N2O5 and NO2 were 10.3 ppt, 122 ppt and 8.3 ppb with median N2O5/NO3 molar ratios of 13.1 and
median nocturnal partitioning of 4.9%. Due to the high levels of NO2
that can inhibit approach to steady-state, we use a method for calculating
NO3 lifetimes that does not assume the steady-state approximation.
Median and average lifetimes of NO3 in the NO3-N2O5 nighttime reservoir were 1.1–2.3 min. We have determined nocturnal
profiles of the pseudo first order loss coefficient of NO3 and the
first order loss coefficients of N2O5 by regression of the
NO3 inverse lifetimes with the [N2O5]/[NO3] ratio.
Direct losses of NO3 are highest early in the night, tapering off as
the night proceeds. The magnitude of the first order loss coefficient of
N2O5 is consistent with, but not verification of, recommended
homogeneous rate coefficients for reaction of N2O5 with water
vapor early in the night, but increases significantly in the latter part of
the night when relative humidity increases beyond 75%, consistent with
heterogeneous reactions of N2O5 with aerosols with a rate constant
khet=(1.2±0.4)×10−3 s−1−(1.6±0.4)×10−3 s−1. Analysis indicates that a correlation exists between overnight
integrated N2O5 concentrations in the marine boundary layer, a
surrogate for the accumulation of chlorine containing photolabile species,
and maximum 1-h average O3 at stations in the Lower Fraser Valley the
next day when there is clear evidence of a sea breeze transporting marine
air into the valley. The range of maximum 1-h average O3 increase
attributable to the correlation is ΔO3=+1.1 to +8.3 ppb
throughout the study for the average of 20 stations, although higher
increases are seen for stations far downwind of the coastal urban area. The
correlation is still statistically significant on the second day after a
nighttime accumulation, but with a different spatial pattern favouring
increased O3 at the coastal urban stations, consistent with transport
of polluted air back to the coast. |
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