The uptake of reactive nitrogen species on ice crystals in cirrus clouds was investigated by simultaneous aircraft-based measurements of gas- and condensed-phase NOy, ice particle size distribution and total aerosol surface area. The measurements were performed in 2000 during the INCA campaign at northern and southern midlatitudes at local autumn. Cirrus ice particles were frequently encountered during these flights in the upper troposphere. Concurrently with the occurrence of cirrus ice particles particulate NOy was observed. It was found that the coverage of the cirrus ice particles with particulate NOy strongly depends on the temperature and the gas-phase NOy concentration. A substantial coverage of the ice particles with values larger than one percent of a monolayer was observed only for temperatures below about 217 K. On average only about one percent of the available gas-phase NOy was found as particulate NOy.