Impact of present and future aircraft NO_xand aerosol emissions on atmospheric composition and associated direct radiative forcing of climate

Abstract

Aviation NO x emissions not only have an impact on global climate by changing ozone and methane levels but also contribute to the deterioration of local air quality. A new version of the LMDZ-INCA global model, including chemistry of both the troposphere and the stratosphere and the sulfate-nitrate-ammonium cycle, is applied to re-evaluate the impact of aircraft NO x and aerosol emissions on climate. The results confirm that the efficiency of NO x to produce ozone is very much dependent on the injection height; it increases with the background methane and NO x concentrations and with decreasing aircraft NO x emissions. The methane lifetime variation is less sensitive to the location of aircraft NO x emissions than the ozone change. The net NO x radiative forcing (RF) (O 3 + CH 4 ) is largely affected by the revised CH 4 RF formula. The ozone positive forcing and the methane negative forcing largely offset each other, resulting in a slightly positive forcing for the present day. However, in the future, the net forcing turns to negative, essentially due to higher methane background concentrations. Additional RFs involving particle formation arise from aircraft NO x emissions since the increased hydroxyl radical (OH) concentrations are responsible for an enhanced conversion of SO 2 to sulfate particles. Aircraft NO x emissions also increase the formation of nitrate particles in the lower troposphere. However, in the upper troposphere, increased sulfate concentrations favour the titration of ammonia leading to lower ammonium nitrate concentrations. The climate forcing of aircraft NO x emissions is likely to be small or even switch to negative (cooling), depending on atmospheric NO x or CH 4 future background concentrations, or when the NO x impact on sulfate and nitrate particles is considered. However, large uncertainties remain for the NO x net impact on climate and in particular on the indirect forcings associated with aerosols, which are even more uncertain than the other forcings from gaseous species. Hence, additional studies with a range of models are needed to provide a more consolidated view. Nevertheless, our results suggest that reducing aircraft NO x emissions is primarily beneficial for improving air quality.

Uncertainties in mitigating aviation non-CO2 emissions for climate and air quality using hydrocarbon fuels

“…A further source of uncertainty in the NO x system is the formation of nitrate particles and their role in radiative forcing, which is generally thought to represent a negative term. 91…”

How do Cl concentrations matter for the simulation of CH4 and δ13C(CH4) and estimation of the CH4 budget through atmospheric inversions?

“…Three-dimensional and time-dependent oxidant concentration fields (OH, O( 1 D), and Cl) were simulated by the GCM LMDz coupled to the INteraction with Chemistry and Aerosols (INCA) model (Hauglustaine et al, 2021;Folberth et al, 2006;Hauglustaine et al, 2004). A total of 17 ozone-depleting substances consisting of chlorofluorocarbons (CFCs; CFC-12, CFC-11, and CFC-113), three hydrochlorofluorocarbons (HCFCs; HCFC-22, HCFC-141b, and HCFC-142b), two halons (halon-1211 and halon-1301), methyl chloroform (CH 3 CCl 3 or MCF), carbon tetrachloride (CCl 4 ), methyl chloride (CH 3 Cl), methylene chloride (CH 2 Cl 2 ), chloroform (CHCl 3 ), methyl bromide (CH 3 Br), and HFC-134a, and their associated photochemical reactions, were included in the INCA chemical scheme to produce Cl radicals (Terrenoire et al, 2022). In the coupled LMDz-INCA simulations, surface concentrations of these long-lived Cl precursors were prescribed based on historical data sets prepared by Meinshausen et al (2017).…”

The climate impact of hydrogen-powered hypersonic transport

“…Earlier versions of the LMDZ-INCA, model including gas-phase tropospheric chemistry, have only been used previously to assess the impact of subsonic aircraft on tropospheric ozone (Koffi et al, 2010;Hauglustaine and Koffi, 2012). This version of the model has been extended to include an interactive chemistry in the stratosphere and mesosphere (Terrenoire et al, 2022). Chemical species and reactions specific to the middle atmosphere have been included in the model.…”

“…In a forthcoming publication, we extend the evaluation to higher altitudes and compare EMAC model results to satellite data (Pletzer and Grewe, 2022). In addition, a comparison between LMDZ-INCA and ozone sounding measurements has also been presented in Terrenoire et al (2022).…”

“…The impact of supersonic aircraft at stratospheric altitudes is often discussed in terms of ozone concentration changes and ultraviolet radiation, and extensive overviews on these topics have recently been published (Zhang et al, 2021;Tuck, 2021;Matthes et al, 2022). The first notes indicating that NO x from supersonics might significantly affect the ozone layer were published in the 1970s (Crutzen, 1970(Crutzen, , 1972Johnston, 1971).…”