An assessment of aircraft as a source of particles to the upper troposphere

Condensation nuclei measurements are examined in conjunction with measurements of reactive nitrogen species (NO y ) to identify aircraft plumes in primary air traffic corridors over the North Atlantic. Several hundred plumes exhibiting ≥100 pptv enhancements in NO y mixing ratio were observed. The plumes were typically a few hundred meters wide, exhibited high NO/NO y ratios, and ranged in age from ∼10 minutes to ∼10 hours. Assuming the sampled aircraft emitted ∼12 g NO x (as NO 2 ) kg −1 fuel burned and that the loss of NO y to the particle phase was negligible, we calculate median aerosol emission indices in terms of number of particles kg −1 of fuel burned of ∼120×10 15 for CN ≥8 nm in size; ∼50×10 15 for CN ≥ 17 nm; and ∼3×10 15 for the nonvolatile CN ≥ 17 nm. Using published fuel burn statistics, background aerosol concentrations, and a 10 day particle lifetime, we conclude that present aviation sources enhance global averaged upper‐tropospheric fine and nonvolatile aerosol number densities by ∼6% and ∼3%, respectively.