Uptake of nitric acid in ice crystals in persistent contrails

Abstract

This is a short version of Schäuble et al. (2009) published in ACPD. In November 2006 cirrus clouds and almost 40 persistent contrails were probed with in situ instruments over Germany and Northern Europe during the CIRRUS-III campaign. At altitudes between 10 and 11.5 km and temperatures of 211 to 220 K contrails with ages up to 8 hours were detected. These contrails had a larger ice phase fraction of total nitric acid (HNO3,ice/HNO3,tot = 6 %) than the ambient cirrus layers (3 %). The differences in ice phase fractions between developing contrails and cirrus are likely caused by high plume concentrations of HNO3 prior to contrail formation and large ice crystal number densities in contrails. The observed decrease of nitric acid to water molar ratios in ice with increasing mean ice particle diameter suggests that ice-bound HNO3 concentrations are controlled by uptake of exhaust HNO3 in the freezing plume aerosol in young contrails and subsequent trapping of ambient HNO3 in growing ice particles in older (age > 1 h) contrails.