Aviation 2006 NOx-induced effects on atmospheric ozone and HOx in Community Earth System Model (CESM)

Other literature type, Article English OPEN
A. Khodayari ; S. Tilmes ; S. C. Olsen ; D. B. Phoenix ; D. J. Wuebbles ; J.-F. Lamarque ; C.-C. Chen (2014)
  • Publisher: Copernicus Publications
  • Journal: Atmospheric Chemistry and Physics (issn: 1680-7316, eissn: 1680-7324)
  • Related identifiers: doi: 10.5194/acp-14-9925-2014
  • Subject: Chemistry | QD1-999 | Physics | QC1-999

The interaction between atmospheric chemistry and ozone (O<sub>3</sub>) in the upper troposphere–lower stratosphere (UTLS) presents a major uncertainty in understanding the effects of aviation on climate. In this study, two configurations of the atmospheric model from the Community Earth System Model (CESM), Community Atmosphere Model with Chemistry, Version 4 (CAM4) and Version 5 (CAM5), are used to evaluate the effects of aircraft nitrogen oxide (NO<sub>x</sub> = NO + NO<sub>2</sub>) emissions on ozone and the background chemistry in the UTLS. CAM4 and CAM5 simulations were both performed with extensive tropospheric and stratospheric chemistry including 133 species and 330 photochemical reactions. CAM5 includes direct and indirect aerosol effects on clouds using a modal aerosol module (MAM), whereby CAM4 uses a bulk aerosol module, which can only simulate the direct effect. To examine the accuracy of the aviation NO<sub>x</sub>-induced ozone distribution in the two models, results from the CAM5 and CAM4 simulations are compared to ozonesonde data. Aviation NO<sub>x</sub> emissions for 2006 were obtained from the AEDT (Aviation Environmental Design Tool) global commercial aircraft emissions inventory. Differences between simulated O<sub>3</sub> concentrations and ozonesonde measurements averaged at representative levels in the troposphere and different regions are 13% in CAM5 and 18% in CAM4. Results show a localized increase in aviation-induced O<sub>3</sub> concentrations at aviation cruise altitudes that stretches from 40° N to the North Pole. The results indicate a greater and more disperse production of aviation NO<sub>x</sub>-induced ozone in CAM5, with the annual tropospheric mean O<sub>3</sub> perturbation of 1.2 ppb (2.4%) for CAM5 and 1.0 ppb (1.9%) for CAM4. The annual mean O<sub>3</sub> perturbation peaks at about 8.2 ppb (6.4%) and 8.8 ppb (5.2%) in CAM5 and CAM4, respectively. Aviation emissions also result in increased hydroxyl radical (OH) concentrations and methane (CH<sub>4</sub>) loss rates, reducing the tropospheric methane lifetime in CAM5 and CAM4 by 1.69 and 1.40%, respectively. Aviation NO<sub>x</sub> emissions are associated with an instantaneous change in global mean short-term O<sub>3</sub> radiative forcing (RF) of 40.3 and 36.5 mWm<sup>−2</sup> in CAM5 and CAM4, respectively.
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