In:
Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 106, No. D9 ( 2001-05-16), p. 9991-10001
Abstract:
Nighttime chemistry of OH, HO 2 , and organic peroxy radicals is examined in different environmental cases of the lower continental troposphere. The scenarios cover a large range of NO x concentrations and various mixtures of anthropogenic and biogenic VOCs. For each scenario the primary formation rate of radicals species is calculated and the evolution of the radical pool is investigated by calculating the efficiency of the propagation reactions versus the termination reactions in the RO 2 → H0 2 → OH cycle. Finally, the net OH formation rates as well as the relative contributions of the NO 3 − and O 3 ‐initiated mechanisms in the OH production are calculated. We found that the radical initiation is driven by ozonolysis of VOC in urban and environments with low NO x concentrations, while both NO 3 and O 3 contribute to the radical initiation in rural sites with moderated NO x levels. The nighttime formation of OH radicals exhibits similarities between the different scenarios. In most of the cases, OH formation at night results mainly from VOC + O 3 reactions in the mixing layer as well as the upper layer of the troposphere. The VOC + NO 3 reactions were found to account for a maximum of 25% in OH production in scenarios with high levels of biogenic compounds and moderated levels of NO x . In the mixing layer the interconversion among radicals (RO 2 → HO 2 and HO 2 → OH conversions), when it happens at night, is essentially driven by NO. The resulting OH fluxes vary from 0.2–1×10 7 to 1×10 6 molecule cm −3 s −1 in the urban scenario in the mixing and top layer, respectively. In rural/remote situations, nighttime fluxes range from 1×10 6 molecule cm −3 s −1 in the mixing layer to 1×10 5 molecule cm −3 s −1 in the upper layer.
Type of Medium:
Online Resource
ISSN:
0148-0227
DOI:
10.1029/2000JD900348
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
2001
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