Measurements of HONO, NO, NOy and SO2 in aircraft exhaust plumes at cruise

Abstract

Measurements of gaseous nitrogen and sulfur oxide emissions in young aircraft exhaust plumes give insight into chemical oxidation processes inside aircraft engines. Particularly, the OH‐induced formation of nitrous acid (HONO) from nitrogen oxide (NO) and sulfuric acid (H2SO4) from sulfur dioxide (SO2) inside the turbine which is highly uncertain, need detailed analysis to address the climate impact of aviation. We report on airborne in situ measurements at cruise altitudes of HONO, NO, NOy, and SO2 in 9 wakes of 8 different types of modern jet airliners, including for the first time also an A380. Measurements of HONO and SO2 were made with an ITCIMS (Ion Trap Chemical Ionization Mass Spectrometer) using a new ion‐reaction scheme involving SF5 − reagent ions. The measured molar ratios HONO/NO and HONO/NOy with averages of 0.038 ± 0.010 and 0.027 ± 0.005 were found to decrease systematically with increasing NOx emission‐index (EI NOx). We calculate an average EI HONO of 0.31 ± 0.12 g NO2 kg−1. Using reliable measurements of HONO and NOy, which are less adhesive than H2SO4 to the inlet walls, we derive the OH‐induced conversion fraction of fuel sulfur to sulfuric acid " with an average of 2.2 ± 0.5 %. " also tends to decrease with increasing EI NOx, consistent with earlier model simulations. The lowestHONO/NO,HONO/NOy and "was observed for the largest passenger aircraft A380.