Quantifying uptake of HNO₃ and H₂O by alumina particles in Athena‐2 rocket plume

The goal of this study is to quantify uptake of H 2 O and HNO 3 by and estimate their residence time on alumina particles in Athena‐2 rocket plumes. This study uses in situ measurements made in the lower stratosphere with the NASA WB‐57F high‐altitude aircraft on 24 September 1999. Constraining the Atmospheric and Environmental Research, Inc. (AER), plume model with available measurements, we found that (1) H 2 O uptake coefficient for alumina particles is larger than 3 × 10 −4 , (2) HNO 3 is produced via ClONO 2 + HCl → Cl 2 + HNO 3 on alumina particles and resides on their surfaces for 5–52 min, and (3) alumina particles in the plume are covered by 100–200 monolayers of adsorbed H 2 O and 0.1–10 monolayers of HNO 3 under lower stratospheric conditions. These values are uncertain by at least a factor of 2. We speculate that the H 2 O coverage remaining on alumina particles accelerates the ClONO 2 + HCl → Cl 2 + HNO 3 reaction, thus leading to a larger than previously thought global ozone loss to solid‐fueled rocket emissions, especially if at least several percent of emitted alumina mass are in submicron particles.