edu.ucar.opensky::articles:6331 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-26T15:25:00.162167 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d7cf9q95 HOx chemistry during INTEX-A 2004: Observation, model calculation, and comparison with previous studies 2008-03-08T00:00:00Z publication https://n2t.org/ark:/85065/d7cf9q95 https://doi.org/10.1029/2007JD009166 Ren, X. author Olson, J. author Crawford, J. author Brune, W. author Mao, J. author Long, R. author Chen, Z. author Chen, G. author Avery, M. author Sachse, G. author Barrick, J. author Diskin, G. author Huey, L. author Fried, Alan author Cohen, R. author Heikes, B. author Wennberg, P. author Singh, H. author Blake, D. author Shetter, Richard E. author UCAR/NCAR - Library publisher OH and HO₂ were measured with the Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) as part of a large measurement suite from the NASA DC-8 aircraft during the Intercontinental Chemical Transport Experiment-A (INTEX-A). This mission, which was conducted mainly over North America and the western Atlantic Ocean in summer 2004, was an excellent test of atmospheric oxidation chemistry. The HOx results from INTEX-A are compared to those from previous campaigns and to results for other related measurements from INTEX-A. Throughout the troposphere, observed OH was generally 0.95 of modeled OH; below 8 km, observed HO₂ was generally 1.20 of modeled HO₂. This observed-to-modeled comparison is similar to that for TRACE-P, another midlatitude study for which the median observed-to-modeled ratio was 1.08 for OH and 1.34 for HO₂, and to that for PEM-TB, a tropical study for which the median observed-to-modeled ratio was 1.17 for OH and 0.97 for HO₂. HO₂ behavior above 8 km was markedly different. The observed-to-modeled HO₂ ratio increased from ~1.2 at 8 km to ~3 at 11 km with the observed-to-modeled ratio correlating with NO. Above 8 km, the observed-to-modeled HO₂ and observed NO were both considerably greater than observations from previous campaigns. In addition, the observed-to-modeled HO₂/OH, which is sensitive to cycling reactions between OH and HO₂, increased from ~1.5 at 8 km to almost 3.5 at 11 km. These discrepancies suggest a large unknown HOx source and additional reactants that cycle HOx from OH to HO₂. In the continental planetary boundary layer, the observed-to-modeled OH ratio increased from 1 when isoprene was less than 0.1 ppbv to over 4 when isoprene was greater than 2 ppbv, suggesting that forests throughout the United States are emitting unknown HOx sources. Progress in resolving these discrepancies requires a focused research activity devoted to further examination of possible unknown OH sinks and HOx sources. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication An edited version of this paper was published by AGU. Copyright 2008 American Geophysical Union. None eng geoscientificInformation