Mass spectra of individual aerosol particles were acquired at altitudes up to 19 km during the WB-57 Aerosol Mission. Fluorine and chlorine were more abundant in tropospheric aerosols than in stratospheric aerosols. Chlorine in tropospheric aerosols was often associated with organics, soot, and mineral dust. Small amounts of perchlorate were observed in stratospheric sulfate aerosols, but aerosols do not represent a significant sink for total fluorine or chlorine in the lower stratosphere. Bromine was most common in aerosols just above the tropopause, where it may represent a significant fraction of inorganic Br. Both bromine and iodine were highly correlated with organics and probably were present in particles with Hg. The OH- and NO+ peak areas increased at temperatures below 195 K, providing evidence for the uptake of H2O and HNO3 by aerosols near a cold tropopause. There was evidence for uptake of chlorine but not the other halogens below 190 K. ¿ 2000 American Geophysical Union