We analyze nearly-simultaneous measurements of ice clouds and pollutants along satellite tracks. We use Aura MLS CO and ice water content measurements at 215 hPa to classify ice clouds as ‘‘clean’’ or ‘‘polluted’’. We then examine Aqua MODIS ice particle effective radius (re) and aerosol optical thickness (AOT) along with TRMM precipitation to investigate how pollution changes ice particle size and precipitation. We find suppressed precipitation and reduced re associated with polluted clouds during the dry season in South America when there is a strong positive correlation between the CO and AOT. In contrast, during the wet season, we find little difference in ice particle size and precipitation between the polluted clouds and the clean clouds, as indicated by the CO levels, when the AOT is significantly lower than that in the dry season.