To conduct the experiments prescribed in this chapter, students should be aware of the hazards associated with the use of all the chemicals, glassware and electrical equipment and so on. Tropospheric ozone is formed by a complex series of photochemical reactions. Stratospheric ozone is produced naturally, although some may be transported to the troposphere by large-scale air movements. Stratospheric ozone is produced naturally, although some may be transported to the troposphere by large-scale air movements. Research studies have focused on urban air quality associated with traffic emissions and rural/remote air quality, particularly within forests to assess the contribution of biogenic carbonyl emissions and their precursors. Carbonyl compounds arise from anthropogenic and biogenic sources, both as primary products and as secondary photochemical products. The concentrations of four carbonyl compounds (e.g. formaldehyde, acetaldehyde, acrolein and crotonaldehyde) can be measured using a method based on the US Environmental Protection Agency Compendium Method TO-11A.