Articles | Volume 18, issue 4
Research article
19 Feb 2018
Research article |  | 19 Feb 2018

Global sensitivity analysis of GEOS-Chem modeled ozone and hydrogen oxides during the INTEX campaigns

Kenneth E. Christian, William H. Brune, Jingqiu Mao, and Xinrong Ren

Abstract. Making sense of modeled atmospheric composition requires not only comparison to in situ measurements but also knowing and quantifying the sensitivity of the model to its input factors. Using a global sensitivity method involving the simultaneous perturbation of many chemical transport model input factors, we find the model uncertainty for ozone (O3), hydroxyl radical (OH), and hydroperoxyl radical (HO2) mixing ratios, and apportion this uncertainty to specific model inputs for the DC-8 flight tracks corresponding to the NASA Intercontinental Chemical Transport Experiment (INTEX) campaigns of 2004 and 2006. In general, when uncertainties in modeled and measured quantities are accounted for, we find agreement between modeled and measured oxidant mixing ratios with the exception of ozone during the Houston flights of the INTEX-B campaign and HO2 for the flights over the northernmost Pacific Ocean during INTEX-B. For ozone and OH, modeled mixing ratios were most sensitive to a bevy of emissions, notably lightning NOx, various surface NOx sources, and isoprene. HO2 mixing ratios were most sensitive to CO and isoprene emissions as well as the aerosol uptake of HO2. With ozone and OH being generally overpredicted by the model, we find better agreement between modeled and measured vertical profiles when reducing NOx emissions from surface as well as lightning sources.

Short summary
We applied a global sensitivity analysis to the GEOS-Chem chemical transport model analyzing some well-studied tropospheric oxidants for a time period corresponding to an aircraft field campaign. We find modeled results generally agree with measurements when uncertainties in both the model and measurements are taken into account. While model results were largely sensitive to emissions, chemical reaction rates also represented a large source of uncertainty.
Final-revised paper