Introduction to special section: Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX) and Pollution From Aircraft Emissions in the North Atlantic Flight Corridor (POLINAT 2)

Emissions of atmospheric species from the engines of subsonic aircraft at cruise altitude (roughly, above 7 km) are of concern to scientists, the aviation industry, and policymakers for two reasons. First, water vapor, soot, and sulfur oxides, and related heterogeneous processes, may modify clouds and aerosols enough to perturb radiative forcing in the upper troposphere/lower stratosphere (UT/LS). A discussion of these phenomena appears in chapter 3 of the Intergovernmental Panel on Climate Change (IPCC) [1999] aviation assessment. An airborne campaign conducted to evaluate aviation effects on contrail, cirrus, and cloud formation is described in Geophysical Research Letters (25(8‐10), 1998).