Speciation and Chemical Evolution of Nitrogen Oxides in Aircraft Exhaust near Airports

Measurements of nitrogen oxides from a variety of commercial aircraft engines as part of the JETS-APEX2 and APEX3 campaigns show that NO x (NOx ≡ NO + NO2) is emitted primarily in the form of NO2 at idle thrust and NO at high thrust. A chemical kinetics combustion model reproduces the observed NO2 and NO x trends with engine power and sheds light on the relevant chemical mechanisms. Experimental evidence is presented of rapid conversion of NO to NO2 in the exhaust plume from engines at low thrust. The rapid conversion and the high NO2/NO x emission ratios observed are unrelated to ozone chemistry. NO2 emissions from a CFM56-3B1 engine account for approximately 25% of the NO x emitted below 3000 feet (916 m) and 50% of NO x emitted below 500 feet (153 m) during a standard ICAO (International Civil Aviation Organization) landing−takeoff cycle. Nitrous acid (HONO) accounts for 0.5% to 7% of NO y emissions from aircraft exhaust depending on thrust and engine type. Implications for photochemistry near airports resulting from aircraft emissions are discussed.