Vertical mixing of commercial aviation emissions from cruise altitude to the surface

Abstract

[1] Data analysis and numerical simulations were used to examine vertical transport of cruise-altitude commercial aircraft emissions to the surface. First, aircraft emission data were compared with static stability and potential temperature data from satellites. Second, we ran global 3-D simulations of a passive tracer released uniformly at 11 km (cruise altitude). We present global, regional, and seasonal results of the data comparisons as well as approximate time scales of vertical mixing derived from the simulations. Using the year 2006 as a case study, we found that 24% of all global commercial aviation emissions occurred in the stratosphere, 17% occurred both north of 40° N and above the 330 K isentrope, and 54% occurred in regions of at least moderate static stability (N2 > 10−4 s−2). In addition, 74% of emissions in the Arctic Circle were in the stratosphere. In the 3-D simulations, the globally averaged tracer-plume e-folding lifetime against vertical transport to any other altitude was 16 days during January and 14 days during July. Furthermore, the passive tracer took 15 days longer in January (77 days) compared with July (62 days) to achieve a surface-to-cruise mixing ratio fraction greater than 0.5 at all latitudes. The dynamical mixing time scales of extratropical cruise-altitude emissions were significantly longer than the globally averaged wet removal time of 4–5 days for aerosol particles emitted in the lower troposphere. Thus, it is unlikely that cruise-altitude emissions affect surface air quality via transport alone outside the tropics.