A Literature Review

This article discusses primary and secondary particulates with respect to their size distribution, origin, and chemical composition. Primary particulates are particles that are injected directly into the atmosphere. Usually their sizes are within the range 1 to 20 jum. Common sources are windblown soil, industrial emissions, and combustion systems. Examples of typical primary particulates are soot, pollen, fly ash, and dust. Secondary particulates are relatively small; their size range is 0.01 to 1.0 nm. They can be generally classified as sulfates, nitrates, or hydrocarbons. Secondary particulates are formed as a result of atmospheric reactions involving gaseous species such as SO2, NO*, O2, NH3, H2O, and hydrocarbons. The proposed mechanisms for a number of these reactions are outlined and their relative importance is discussed. The impact of both primary and secondary particulates on health and esthetics is also discussed.