Abstract: The latitude-altitude map of ammonia mixing ratio shows an ammonia-rich zone at 0-5degN, with mixing ratios of 320-340 ppm, extending from 40-60 bars up to the ammonia cloud base at 0.7 bars. Ammonia-poor air occupies a belt from 5-20degN. We argue that downdrafts as well as updrafts are needed in the 0-5degN zone to balance the upward ammonia flux. Outside the 0-20degN region, the belt-zone signature is weaker. At latitudes out to +/-40deg, there is an ammonia-rich layer from cloud base down…