Perspectives on NO, NO(y) and fine aerosol sources and variability during SONEX

Distributions of upper tropospheric tracer data on each of the 14 science flights of SONEX (SASS [Subsonics Assessment] Ozone and Nitrogen Oxides Experiment) provide a statistical overview of NO, NO(y) and fine aerosol variability during SONEX (an aircraft mission conducted in October and November 1997). The wide range of variability of NO from all sources provides a perspective on the aircraft perturbation. Background distributions of NO(y) are somewhat elevated inside flight corridors relative to outside; fine aerosol and NO/NO(y) in and out of corridors are similar. The potential vorticity of air sampled during SONEX is low relative to the NAFC (North Atlantic Flight Corridor) as a whole, due either to advection of lower latitude air into the corridor or biases in sampling to avoid the stratosphere. High NO/NO(y) (>0.4) from fresh lightning and aircraft sources was usually associated with pv much lower than the NAFC as a whole. Air masses identified as tropospheric by a low ozone criterion nevertheless have high pv, a marker for stratospheric air. Thus, stratospheric and surface sources also contribute to overall variability. A statistically robust assessment of the relative aircraft NO contribution during SONEX, based on data alone, is unlikely, given the mixture of other NO sources within which the aircraft signal is embedded. This underscores the need for more data and modeling studies.