Particulate Emissions from Aviation:
Sulfates & Soot Aerosols
Aircraft emissions of sulfates and soot particles also affect climate. Direct sulfate emissions cause cooling because sulfates reflect sunlight, while direct soot emissions have a warming effect, since the dark soot particles (black carbon) absorb solar radiation and decrease albedo when deposited over snow.
These anthropogenic (human-caused) aerosols are short-lived. The warming and cooling impact of aerosols from aircraft emissions is currently poorly understood.
The warming effects of soot are reduced at high altitude. Light-scattering particles, on the other hand, are less altitude-dependent in their effects. Also, climate responses can vary with location of emission. For example, soot emissions have a stronger warming effect when emitted over white surfaces, e.g. aircraft flying over the snow- and ice-covered Arctic.
Aircraft sulfate particles can also impact climate change by influencing cloud formation. Water vapor in saturated air can condense on certain particles (ice nucleation), resulting in contrails and cirrus clouds. The exact impact of soot from air travel emissions is not well understood because of the many factors that influence its efficacy in causing cloud formations. These factors include, but are not limited to, natural particle concentrations, temperature fluctuations, and humidity levels. The warming impact of enhanced cloud formation due to aerosols acts on a shorter time scale than the effects of most GHGs and is currently poorly understood.
The direct effect of particles from aircraft is fairly well understood and is estimated to be a small effect. Indirect effects, however, are poorly understood.