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Chemistry of HO_x radicals in the upper troposphere

Jaeglé, Lyatt and Jacob, Daniel J. and Brune, William H. and Wennberg, Paul O. (2001) Chemistry of HO_x radicals in the upper troposphere. Atmospheric Environment, 35 (3). pp. 469-489. ISSN 1352-2310. doi:10.1016/S1352-2310(00)00376-9.

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Aircraft observations from three recent missions (STRAT, SUCCESS, SONEX) are synthesized into a theoretical analysis of the factors controlling the concentrations of HO_x radicals (HO_x=OH+peroxy) and the larger reservoir family HO_y (HO_y=HO_x+2H_2O_2+2CH_3OOH+HNO_2+HNO_4) in the upper troposphere. Photochemical model calculations capture 66% of the variance of observed HOx concentrations. Two master variables are found to determine the variance of the 24 h average HOx concentrations: the primary HO_x production rate, P(HO_x), and the concentration of nitrogen oxide radicals (NO_x=NO+NO_2). We use these two variables as a coordinate system to diagnose the photochemistry of the upper troposphere and map the different chemical regimes. Primary HO_x production is dominated by the O(^1D)+H_2O reaction when [H_2O]>100 ppmv, and by photolysis of acetone (and possibly other convected HO_x precursors) under drier conditions. For the principally northern midlatitude conditions sampled by the aircraft missions, the HO_x yield from acetone photolysis ranges from 2 to 3. Methane oxidation amplifies the primary HO_x source by a factor of 1.1–1.9. Chemical cycling within the HO_x family has a chain length of 2.5–7, while cycling between the HO_x family and its HO_y reservoirs has a chain length of 1.6–2.2. The number of ozone molecules produced per HO_y molecule consumed ranges from 4 to 12, such that ozone production rates vary between 0.3 and 5 ppbv d^(−1) in the upper troposphere. Three chemical regimes (NO_x-limited, transition, NO_x-saturated) are identified to describe the dependence of HO_x concentrations and ozone production rates on the two master variables P(HO_x) and [NO_x]. Simplified analytical expressions are derived to express these dependences as power laws for each regime. By applying an eigenlifetime analysis to the HO_x–NO_x–O_3 chemical system, we find that the decay of a perturbation to HO_y in the upper troposphere (as from deep convection) is represented by four dominant modes with the longest time scale being factors of 2–3 times longer than the steady-state lifetime of HO_y.

Item Type:Article
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URLURL TypeDescription
Jacob, Daniel J.0000-0002-6373-3100
Brune, William H.0000-0002-1609-4051
Wennberg, Paul O.0000-0002-6126-3854
Alternate Title:Chemistry of HOx radicals in the upper troposphere
Additional Information:© 2000 Elsevier Science Ltd. Received 1 March 2000; accepted 5 July 2000. This work was supported by the National Science Foundation (NSF) and by the National Aeronautics and Space Administration (NASA).
Funding AgencyGrant Number
Subject Keywords:Hydrogen oxides; Nitrogen oxides; Tropospheric ozone; Upper troposphere; Aircraft measurements
Issue or Number:3
Record Number:CaltechAUTHORS:20140624-132838956
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Official Citation:Lyatt Jaeglé, Daniel J Jacob, William H Brune, Paul O Wennberg, Chemistry of HOx radicals in the upper troposphere, Atmospheric Environment, Volume 35, Issue 3, 2001, Pages 469-489, ISSN 1352-2310, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46476
Deposited By: Ruth Sustaita
Deposited On:24 Jun 2014 20:52
Last Modified:10 Nov 2021 17:26

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