Abstract: A method and apparatus for determining the level of sufuric acid in atmospheric air which also contains other interferrants, including a sampling cycle to collect sulfuric acid on the walls of a collection chamber tube which is cooled, while at the same time eliminating interfering sulfur dioxide and ammonia by treating them with a dilute flow of hydrochloric acid through the collection chamber, and further including an analysis cycle during which the walls of the collection chamber tube are heated so as to revolatilize the sulfuric acid and entrain it in a clean air stream which then passes to the burner block of a flame photometric detector, the clean air stream being saturated with water vapor to make the revaporization of sulfuric acid more rapid and complete.