Reduction of water, CO2 and N2O in an air stream comprising: passing said air stream at a feed temperature through a first adsorbent, whose Henry's Law selectivity for CO2/N2O is at least 12.5, and a second adsorbent, whose Henry's Law constant for CO2 is less than 1020 mmol/g/atom and whose Henry's Law selectivity for CO2/N2O is at most 5; and passing a heated regenerating gas at a temperature which is between 20° C. and 80° C. to at least the second adsorbent, and passing a second regenerating gas at a temperature less than the temperature of the heated regenerating gas to the first and second adsorbents in a direction opposite to the feed direction; the second adsorbent occupying from 25% to 40% of the total volume of the adsorbents, and the temperature of the heated regenerating gas being 10° C. to 60° C. higher than the feed temperature.