A004-0004
Dominant formation pathways and impacts for aerosols resulting from aviation emissions

Monday, 7 December 2020
Poster
Prakash Prashanth1, Sebastian David Eastham2, Raymond L Speth1 and Steven R H Barrett2, (1)Massachusetts Institute of Technology, Aeronautics and Astronautics, Cambridge, MA, United States, (2)Massachusetts Institute of Technology, Laboratory for Aviation and the Environment, Cambridge, MA, United States
Abstract:
Aerosols resulting from aviation emissions are responsible for ~10,000 premature mortalities annually, and may have disproportionate impacts on clouds and radiation due to their altitude. However, the relative contribution and mechanisms of secondary aerosols (as opposed to direct aerosol emissions) are poorly understood, including how short-lived aerosol precursors at altitude are able to significantly increase surface-level aerosol concentrations.

We apply global chemistry transport modeling to identify and quantify the contributions of different chemical pathways to aviation-attributable aerosol formation, including the resulting impacts on radiative forcing (RF). We estimate that aviation emissions result in a net aerosol radiative forcing of –8.6 Wm-2, of which –0.66 and –7.7 mWm-2 result from nitrate and sulfate aerosols respectively. However, this aerosol effect is disproportionately due to aviation NOx rather than SOx emissions. We find that aviation NOx causes –1.7 mWm-2 through nitrate aerosol forcing but also –1.5 mWm-2 of the larger sulfate aerosol forcing, ~20% of the total. This means that NOx emissions are responsible for ~37% of the net aerosol-attributable RF. We show that this is due to a combination of ozone-mediated oxidation of background sulfur and the “nitrate bounce-back" effect, which reduces the net impact of sulfur emissions.

This ozone-mediated mechanism also explains the ability of cruise aviation emissions to significantly affect surface aerosol concentrations. We find that aviation NOx emissions are responsible for 72% of aviation-attributable, near-surface aerosol loading, compared to 27% from aviation SOx emissions and less than 0.1% from direct emission of black carbon. Aviation NOx and SOx emissions are therefore the primary species responsible for all of aviation attributable aerosol radiative forcing, where in particular the effect of background aerosol precursors is amplified as a result of enhanced production of aviation attributable oxidants at cruise altitudes.

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