Transport impacts on atmosphere and climate: Aviation

Abstract

a b s t r a c tAviation alters the composition of the atmosphere globally and can thus drive climate change and ozone depletion. The last major international assessment of these impacts was made by the Intergovernmental Panel on Climate Change (IPCC) in 1999. Here, a comprehensive updated assessment of aviation is provided. Scientific advances since the 1999 assessment have reduced key uncertainties, sharpening the quantitative evaluation, yet the basic conclusions remain the same. The climate impact of aviation is driven by long-term impacts from CO 2 emissions and shorter-term impacts from non-CO 2 emissions and effects, which include the emissions of water vapour, particles and nitrogen oxides (NO x ). The presentday radiative forcing from aviation (2005) is estimated to be 55 mW m À2 (excluding cirrus cloud enhancement), which represents some 3.5% (range 1.3-10%, 90% likelihood range) of current anthropogenic forcing, or 78 mW m À2 including cirrus cloud enhancement, representing 4.9% of current forcing (range 2-14%, 90% likelihood range). According to two SRES-compatible scenarios, future forcings may increase by factors of 3-4 over 2000 levels, in 2050. The effects of aviation emissions of CO 2 on global mean surface temperature last for many hundreds of years (in common with other sources), whilst its non-CO 2 effects on temperature last for decades. Much progress has been made in the last ten years on characterizing emissions, although major uncertainties remain over the nature of particles. Emissions of NO x result in production of ozone, a climate warming gas, and the reduction of ambient methane (a cooling effect) although the overall balance is warming, based upon current understanding. These NO x emissions from current subsonic aviation do not appear to deplete stratospheric ozone. Despite the progress made on modelling aviation's impacts on tropospheric chemistry, there remains a significant spread in model results. The knowledge of aviation's impacts on cloudiness has also improved: a limited number of studies have demonstrated an increase in cirrus cloud attributable to aviation although the magnitude varies: however, these trend analyses may be impacted by satellite artefacts. The effect of aviation particles on clouds (with and without contrails) may give rise to either a positive forcing or a negative forcing: the modelling and the underlying processes are highly uncertain, although the overall effect of contrails and enhanced cloudiness is considered to be a positive forcing and could be substantial, compared with other effects. The debate over quantification of aviation impacts has also progressed towards studying potential mitigation and the technological and atmospheric tradeoffs. Current studies are still relatively immature and more work is required to determine optimal technological development paths, which is an aspect that atmospheric science has much to contribute. In terms of alternative fuels, liquid hydrogen represents a possibility and may reduce some of aviation's impacts on clim...

Updated Correlation Between Aircraft Smoke Number and Black Carbon Concentration

“…In the atmosphere, BC particles strongly absorb incoming solar radiation and influence cloud formation processes leading to highly uncertain, but likely net positive warming of the earth's atmosphere (Lee et al 2010;Bond et al 2013). BC particles emitted by aircraft engines also contribute to the degradation of air quality both in the vicinity of airports (Yim et al 2013) and globally (Barrett et al 2010).…”

Composition and Sources of the Organic Particle Emissions from Aircraft Engines

“…As submicron particles, gas turbine engine particle material (PM) emissions may potentially impact human health (Stettler et al 2011;Levy et al 2012), local air quality (Dodson et al 2009;Arunachalam et al 2011;Hsu et al 2011Hsu et al , 2012Zhu et al 2011), and global climate (Lee et al 2010;Dallara et al 2011;Dorbian et al 2011;Jacobson et al 2011;Unger 2011). Since aircraft use is predicted to increase in the coming decades (Lee et al 2009) and since post-treatment of aircraft engine exhaust is not feasible, better understanding of the combustion emissions is required so that the potential impacts can be properly accounted for in atmospheric models and to improve aircraft combustor designs.…”

Uncertainties in climate assessment for the case of aviation NO

“…To understand and attribute changes in the greenhouse gases and aerosols that force climate change, we rely on chemistry-transport models (CTMs), which require further characterization of their errors (e.g., [2][3][4][5]. Aviation emissions are estimated to contribute 5% of anthropogenic climate forcing, with a nearly threefold uncertainty (6). This forcing occurs mainly through aviation-induced cloudiness and emissions of CO 2 and nitrogen oxides.…”

“…This forcing occurs mainly through aviation-induced cloudiness and emissions of CO 2 and nitrogen oxides. Climate impacts of other aviation emissions-CO, SO 2 , soot, hydrocarbons, and water vapor-are highly uncertain, but estimated to be much smaller (6). In this paper we quantify one type of climate forcing and its uncertainty, the impact of aviation emissions on the greenhouse gases ozone (O 3 ) and methane (CH 4 ).…”