Perspectives on NO, NOy and fine aerosol sources and variability during SONEX

Distributions of upper tropospheric tracer data on each of the 14 science f lights of SONEX (SASS [Subsonics Assessment] Ozone and Nitrogen Oxides Expe riment) provide a statistical overview of NO, NOy and fine aerosol variabil ity during SONEX tan aircraft mission conducted in October and November 199 7). The wide range of variability of NO from all sources provides a perspec tive on the aircraft perturbation. Background distributions of NOy are some what elevated inside flight corridors relative to outside; fine aerosol and NO/NOy in and out of corridors are similar. The potential vorticity of air sampled during SONEX is low relative to the NAFC (North Atlantic Flight Co rridor) as a whole, due either to advection of lower latitude air into the corridor or biases in sampling to avoid the stratosphere. High NO/NOy (>0.4 ) from fresh lightning acid 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 stratosph eric air. Thus, stratospheric and surface sources also contribute to overal l variability. A statistically robust assessment of the relative aircraft N O contribution during SONEX, based on data alone, is unlikely, given the mi xture of other NO sources within which the aircraft signal is embedded. Thi s underscores the need for more data and modeling studies.