Ozone production in the upper troposphere and the influence of aircraft during SONEX: Approach of NOx-saturated conditions

During October/November 1997, simultaneous observations of NO, HO2 and othe r species were obtained as part of the SONEX campaign in the upper troposph ere. We use these observations, over the North Atlantic (40-60 degrees N), to derive ozone production rates, P(O-3), and to examine the relationship b etween P(O-3) and the concentrations of NOx (= NO + NO2) and HOx (= OH + pe roxy) radicals. A positive correlation is found between P(O-3) and NOx over the entire data set, which reflects the association of elevated HOx with e levated NOx injected by deep convection and lightning. By filtering out thi s association we find that for NOx>70 pptv, P(O-3) is nearly independent of NOx, showing the approach of NOx-saturated conditions. Predicted doubling of aircraft emissions in the future will result in less than doubling of th e aircraft contribution to ozone over the North Atlantic in the fall. Great er sensitivity to aircraft emissions would be expected in the summer.