Volatile organic compounds (VOCs) are defined as organic compounds that vaporize readily and whose vapors may react photochemically in the atmosphere to form ozone, or what is popularly called "smog." VOCs are used as solvents and key raw materials in a wide variety of industrial applications, from organic chemical synthesis to surface coating processes. A portion of the solvent inevitably volatilizes into the atmosphere, producing emissions that are diverse in both composition and flow. Emission streams contain a wide range of VOC concentrations, from less than 1 percent to almost 100 percent, but most are of relatively high concentration. Some emission streams are continuous, while others are intermittent. Process emissions also differ in temperature, pressure, and miscibility. All these factors are important in the selection and design of air pollution control equipment that will effectively reduce VOC emissions.

Control techniques used in industry fall into two broad categories: combustion techniques and recovery techniques. Combustion techniques, such as flares and incinerators, utilize combustion as an oxidation technique to destroy the VOC by converting it to carbon dioxide and water. Recovery techniques, such as carbon adsorption, condensation and absorption, reduce VOC emissions by restoring them to a liquid state. These organic compounds are then recovered from the emission stream for possible resale or reuse in the process. In addition to these broad categories, there are some emerging technologies, including biofiltration, membrane separation processes and photocatalytic oxidation. A third approach to VOC control is process modification, such as substituting a water-based ink for a solvent-based ink, or a low-solvent-content coating for a high-solvent coating. These measures lower VOC emissions by reducing the amount of VOCs used in the process.