In this paper, we discuss results from an experiment conducted on natural aerosol in a clean Arctic environment during the spring. The aerosol behaved as though coated with a volatile film, possibly of sulfuric acid. The thermography of the aerosol observed is consistent with a small fraction of the sulfate being neutralized by ammonium as evidenced by an ammonium to sulfate ratio of 0.14. The volatility behavior of the aerosol is also consistent with an increase in the ammonium to sulfate ratio to 0.39 over one day. The change in the ammonium to sulfate ratio and aerosol volume is consistent with 10 pptv of ammonia in the atmosphere being lost to the aerosol during the period. These values are consistent with others observed in the Arctic winter. ¿ 1997 American Geophysical Union