Effect of NOx emissions from lightning on the production of aviation-induced ozone

Thursday, 18 December 2014
Arezoo Khodayari, Daniel B Phoenix and Donald J Wuebbles, University of Illinois at Urbana Champaign, Department of Atmospheric Sciences, Urbana, IL, United States
Due to the non-linear nature of ozone production in the troposphere, ozone (O3) production as a function of aviation NOx emissions varies based on the background NOx and VOCs levels. Of the several sources of NOx in the atmosphere, NOx from lightning contributes a substantial amount of NOx to the upper troposphere and has an effect on the ozone production efficiency. In this study, CAM5, the atmospheric component of the Community Earth System Model (CESM) was used to study the effect of lightning NOx (LNOx) on the production of O3 in the background atmosphere and on the production of aviation NOx-induced O3 for the year 2006. Currently, there is wide range of uncertainty in aviation NOx-induced effects on O3 among the models. This study shows that one major contributor to this uncertainty is the amount of NOx emissions from lightning. Three simulations were run with varying LNOx values of 3.7, 5.0, and 7.4 TgN/yr. Results show that due to the different background concentrations of NOx and VOCs near the surface nd at cruise altitudes where majority of aircraft fly, varying LNOx impacts the production of the global mean O3 in the background atmosphere and the aviation NOx-induced O3 differently. Increasing LNOx results in an increase in the global mean background O3 production and a stronger decrease in the aviation NOx-induced O3 production due to the low NOx and high VOCs conditions at most attitudes and high NOx and low VOCs conditions at cruise altitudes. By increasing LNOx emissions from 3.7 to 7.4 TgN/yr the global mean O3 production increases from 0.33 to 0.36 Pg (~10% increase) whereas the aviation-induced ozone production decreases from 8.8 to 7.2 Tg (~20% decrease). Similarly, the aviation-induced O3 RF decreases from 43.9 mW/m2 for the 3.7 TgN/yr case to 34.3 mW/m2 for 7.4 TgN/yr case. These results should aid the intercomparions of aviation NOx-induced effects between different models in light of differences in their amounts of NOx emissions from lightning.