The air pollutant secondary organic aerosol (SOA) forms when ammonia and amines react with oxygenated species. When ammonia is present when alkenes react with ozone, SOA increases in size and numbers. This may be due to Criegee intermediates. New research found that a particular amine, dimethylamine, reacts 34,000 times faster with one version of the Criegee intermediate acetaldehyde oxide than with another version of the same compound.