Compressor stations maintain the pressure and flow of natural gas by receiving gas from a pipeline, re-pressurizing it, and sending it back into the pipeline system. Compressor stations can vary in size and are typically placed every 40 to 100 miles along a pipeline or near well sites and pollute the air for 24 hours a day, as long as gas is flowing through the pipeline. Compressor stations emit many of the same toxic pollutants into the air as unconventional wells but on a more consistent basis and over a longer period of time. The largest amount of emissions at compressor stations occur during blowdown periods, when natural gas is released through a blowdown vent, either intentionally, to control flow and pressure, and sometimes accidentally.

Natural gas processing plants are facilities that “clean” raw natural gas to produce what is known as “pipeline quality” dry natural gas and also recover natural gas liquids and substances, such as sulfur. Like compressor stations, processing plants constantly release harmful emissions into the air at varying levels, but emit greater amounts of pollutants into the air than both unconventional wells and compressors stations. Processing plants tend to have frequent, large-scale flaring events to burn off gases that produce high levels of harmful pollutants.  Processing plants also have more opportunities for fugitive emissions (leaks and other irregular releases of gases) than compressor stations.