We examine the effect of nanometer-sized aircraft-induced aqueous sulfuric acid (H2SO4/H2O) particles on atmospheric ozone as a function of temperature. Our calculations are based on a previously derived parameterization for the regional-scale perturbations of the sulfate surface area density due to air traffic in the North Atlantic Flight Corridor (NAFC) and a chemical box model. We confirm large scale model results that at temperatures T>210 K additional ozone loss -- mainly caused by hydrolysis of BrONO2 and N2O5 -- scales in proportion with the aviation-produced increase of the background aerosol surface area. However, at lower temperatures (< 210 K) we isolate two effects which efficiently reduce the aircraft-induced perturbation: (1) background particles growth due to H2O and HNO3 uptake enhance scavenging losses of aviation-produced liquid particles and (2) the Kelvin effect efficiently limits chlorine activation on the small aircraft-induced droplets by reducing the solubility of chemically reacting species. These two effects lead to a substantial reduction of heterogeneous chemistry on aircraft-induced volatile aerosols under cold conditions. In contrast we find contrail ice particles to be potentially important for heterogeneous chlorine activation and reductions in ozone levels. These features have not been taken into consideration in previous global studies of the atmospheric impact of aviation. Therefore, to parameterize them in global chemistry and transport models, we propose the following parameterisation: scale the hydrolysis reactions by the aircraft-induced surface area increase, and neglect heterogeneous chlorine reactions on liquid plume particles but not on ice contrails and aircraft induced ice clouds.
An aircraft plume model has been developed on the basis of two coupled trajectory box models. Two boxes, one for plume and one for background conditions, are coupled by means of a mixing parameterization based on turbulence theory. The model considers comprehensive gas phase chemistry for the tropopause region including acetone, ethane and their oxidation products. Heterogeneous halogen, N2O5 and HOx chemistry on various types of background and aircraft-induced aerosols (liquid and ice) is considered, using state-of-the-art solubility dependent uptake coefficients for liquid phase reactions. The microphysical scheme allows for coagulation, gas-diffusive particle growth and evaporation, so that the particle development from 1s after emission to several days can be simulated. Model results are shown, studying emissions into the upper troposphere as well as into the lowermost stratosphere for contrail and non-contrail conditions. We show the microphysical and chemical evolution of spreading plumes and use the concept of mean plume encounter time, tl, to define effective emission and perturbation indices (EEIs and EPIs) for the North Atlantic Flight Corridor (NAFC) showing EEI(NOy) and EPI(O3) for various background conditions, such as relative humidity, local time of emission, and seasonal variations. Our results show a high sensitivity of EEI and EPIs on the exact conditions under which emissions take place. The difference of EEIs with and without considering plume processes indicates that these processes cannot be neglected.
