Aerosol dynamics in near‐field aircraft plumes

Abstract

A numerical model including gas phase HO x , NO x , and SO x chemistry; H 2 SO 4 ‐soot adsorption; binary H 2 SO 4 ‐H 2 O nucleation; aerosol coagulation; and vapor condensation is used to investigate aerosol formation and growth in near‐field aircraft plumes. The plume flow field is treated using the JANNAF standard plume flow field code, SPF‐II. Model results are presented for a Mach 2.4 high‐speed civil transport at 18 km altitude and 85°N latitude and a subsonic Boeing 707 at 12.2 km, 47°N. The results, based on hydroxyl radical driven oxidation kinetics, indicate that 1–2% of the emitted SO 2 is converted to H 2 SO 4 in the near‐field exhaust (1–2 s) and that for typical exhaust SO 2 emission indices (≈1 g kg‐fuel) the plume is supersaturated with respect to both the pure liquid acid and H 2 SO 4 /H 2 O solutions. Classical nucleation theory predicts high levels of small (0.3–0.6 nm radius) H 2 SO 4 /H 2 O embryos. Coagulation and gas‐to‐particle conversion are followed to provide estimates for the number density of activated soot particles capable of serving as condensation nuclei for contrail formation. Results are presented illustrating the dependence of water condensation on the number density and size distribution of activated exhaust soot nuclei.