Abstract
Abstract. The interaction between atmospheric chemistry and ozone (O3) 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 (NOx = NO + NO2) 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 NOx-induced ozone distribution in the two models, results from the CAM5 and CAM4 simulations are compared to ozonesonde data. Aviation NOx emissions for 2006 were obtained from the AEDT (Aviation Environmental Design Tool) global commercial aircraft emissions inventory. Differences between simulated O3 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 O3 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 NOx-induced ozone in CAM5, with the annual tropospheric mean O3 perturbation of 1.2 ppb (2.4%) for CAM5 and 1.0 ppb (1.9%) for CAM4. The annual mean O3 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 (CH4) loss rates, reducing the tropospheric methane lifetime in CAM5 and CAM4 by 1.69 and 1.40%, respectively. Aviation NOx emissions are associated with an instantaneous change in global mean short-term O3 radiative forcing (RF) of 40.3 and 36.5 mWm−2 in CAM5 and CAM4, respectively.
Highlights
The aviation industry has grown rapidly since its nascence, at a rate of 9 % per year for passenger traffic between 1960 and 2000 (IPCC, 1999) and is one of the fastest growing transportation sectors (IPCC, 2007)
We examine the effect of aviation NOx emissions on the atmospheric concentration of O3 and hydrogen oxide radicals (HOx = OH + HO2) and the reduction of CH4 lifetime using the latest versions of the atmospheric components of the Community Earth System Model (CESM) model, namely the Community Atmosphere Model with Chemistry, Version 4 (CAM4) and Version 5 (CAM5)
This study is the first evaluation of aviation NOx effects in CAM5 which simulates the size distribution of aerosols, both internal and external mixing of aerosols, and chemical and optical properties of aerosols
Summary
The aviation industry has grown rapidly since its nascence, at a rate of 9 % per year for passenger traffic between 1960 and 2000 (IPCC, 1999) and is one of the fastest growing transportation sectors (IPCC, 2007). The aviation NOx-induced changes in O3 calculated in these studies varies between 0.46 and 0.90 Dobson units of ozone per TgN per year (DU(O3) [TgN yr−1]−1). Stevenson et al (2004) looked at the effects of an extra pulse of aviation-induced NOx at four months representing the seasonal cycle Their results showed a seasonal dependence in the O3 radiative forcing with a long-term net radiative forcing of approximately zero. As reported in Holmes et al (2011), modelbased estimates of aviation NOx-induced changes in O3 vary by up to 100 %, largely because of differences between models in the ratios of NO : NO2 and OH : HO2, background NOx levels, location and time of emissions, the amount of sunlight, and in atmospheric mixing (Holmes et al, 2011).
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