An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Managing Air Quality - Emissions Measurement

Emissions measurement is the process of measuring the amount of pollutants, in a gaseous or particulate form, being emitted to the air from a specific source, such as an industrial process.

Measurements of emissions can be used to understand the relative importance of a given source compared to other sources and in developing emissions inventories.

Government or industry personnel use emissions measurements to assess the performance of control strategies. The gas stream can be measured before and after a pollution control device to determine how efficiently it captures pollutants. Emission measurements also are used to determine compliance with regulations limiting the amount of pollution that a source may emit.

Measurements can be taken over a short time period (e.g., hours), often referred to as a source test, or with methods that measure on a continuous basis, often called continuous emissions monitoring. Either way, it is important obtain data from samples that are representative of the emission stream using methods that are reliable.

Resources for EPA’s methods for measuring emissions