In situ observations and model calculations of black carbon emission by aircraft at cruise altitude

The exhaust aerosol of two aircraft at cruise was extensively characterized in the size range from 0.003 to 2 μm for plume ages ≤2 s. The black carbon (BC) exhaust aerosol of an older technology engine (Rolls‐Royce/Snecma M45H Mk501) consisted of a primary BC mode with a modal diameter of 0.035 μm and a mode of coagulated BC particles with a peak near 0.15–0.16 μm in diameter. The total number density at the nozzle exit plane was 3×10 7 cm −3 . In contrast, a modern technology engine (CFM International CFM56‐3B1) emitted far smaller BC particles with a primary mode at 0.025 μm and a coagulated mode at 0.15 μm, as well as fewer particles by number with a concentration of 9×10 6 cm −3 . The single‐scattering albedo of the jet exhaust aerosol was 0.035 ± 0.02 inside the plume, indicating a dominant contribution of ultrafine ( D <0.1 μm) BC particles to light extinction. Black carbon number emission indices EI(N) varied from 3.5×10 14 (CFM56‐3B1) to 1.7×10 15 kg −1 (M45H Mk501) with corresponding mass emission indices EI(BC) of 0.011 and 0.1 g kg −1 . Previously reported corresponding values for a CF6‐80C2A2 engine were 6×10 14 kg −1 and 0.023 g kg −1 , respectively. A comparison between EI(BC) values calculated by a new correlation method and measured data shows an excellent agreement, with deviations <10% at cruise conditions. By extending the EI(BC) calculation method to a globally operating aircraft fleet, a fleet‐averaged emission index EI(BC) = 0.038 g kg −1 is calculated.