OH in the tropical upper troposphere and its relationships to solar radiation and reactive nitrogen
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In situ measurements of [OH], [HO2] (square brackets denote species concentrations), and other chemical species were made in the tropical upper troposphere (TUT). [OH] showed a robust correlation with solar zenith angle. Beyond this dependence, however, [OH] did not correlate to its primary source, the product of [O3] and [H2O] ([O3]•[H2O]), or its sink [NOy]. This suggests that [OH] is heavily buffered in the TUT. One important exception to this result is found in regions with very low [O3], [NO], and [NOy]. Under these conditions, [OH] is highly suppressed, pointing to the critical role of NO in sustaining OH in the TUT and the possibility of low [OH] over the western Pacific warm pool due to strong marine convections bringing NO-poor air to the TUT. In contrast to [OH], [HOx] ([OH] + [HO2]) correlated reasonably well with [O3]•[H2O]/[NOy], suggesting that [O3]•[H2O] and [NOy] are the significant source and sink, respectively, of [HOx].
KeywordsOH In situ Tropical upper troposphere STRAT
This work was supported by the NOAA Atmospheric Composition and Climate Program and the NOAA Health of the Atmosphere Program, the NASA Radiation Sciences Program, and the NASA Upper Atmosphere Research Program. We would like to thank the NASA ER-2 program for making the mission possible. We thank M. Rex and L. L. Pan for insightful discussions.
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