Modelling aerosol deposition rates on aircraft and implications for pollutant accumulation and corrosion

Although corrosion of airframes is a major issue for both commercial and military air fleets, little work has been carried out on how the pollutants that promote corrosion on airframes are deposited (particularly in flight). In this study, a model has been developed that defines the efficiency of aerosol deposition on the leading edges of aircraft as a function of both aerosol size and airspeed. Deposition only occurs with aerosols in the medium size range, with small aerosols remaining in the airstream and large aerosols depositing on but then splashing off an airframe. However, the size range of particles that are deposited decreases with increasing airspeed. Modelling indicates that aerosols in the size range that can readily deposit in flight will remain stable on an airframe and will not be readily blown off. This knowledge of aerosol deposition efficiency enables calculations of total in-flight depositions while factoring in different locations, types of flights and environmental severity. It is estimated that deposition in flight through clouds may be quite significant, as cloud condensation nuclei are in a suitable range for deposition. The relative extents of aerosol deposition during flight and on ground are compared, and it is found that for certain combinations of airfield location and flight scenario, deposition during flight may be comparable to or exceed deposition on the ground.