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

Making sense of modeled atmospheric composition requires not just 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 5 the DC-8 flight tracks corresponding to the NASA 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
10 and isoprene emissions as well as the aerosol uptake of HO2.With ozone and OH being generally over predicted by the model,
we find better agreement between modeled and measured vertical profiles when reducing NOx emissions from surface as well
as lightning sources.