Compressor stations are large industrial facilities that maintain the flow and pressure of natural gas by receiving gas from the pipeline, re-pressurizing it, and sending it back into the pipeline system. (Pump stations do the same thing for oil.)
Compressors are generally constructed every 40-100 miles along a pipeline, depending on the terrain and capacity of both the pipeline and the station.
While some older stations contain only one or two engines, newer or expanded ones can have six or more engines. Each engine has a stack, which is a key source of air pollution. Engines run on diesel, natural gas, or electricity.
- carbon monoxide (CO);
- nitrogen oxides (NOx);
- fine and coarse particulate matter (PM2.5 and PM10);
- sulfur dioxides (SOx);
- volatile organic compounds (VOCs);
- hazardous air pollutants (HAPs) (e.g., formaldehyde, benzene, toluene, and xylene); and
- greenhouse gases (methane, carbon dioxide, and nitrous oxide).
Because they run engines and have a variety of equipment that can leak, compressor stations pollute the air whenever they operate. Pollution can be particularly intense during scheduled or accidental “blowdown” events, when pressure builds to the point where gas is vented directly into the air in order to prevent explosions.
Compressor stations and other gas development operations can be noisy enough to pose health risks by causing stress, sleep deprivation, and elevated blood pressure. Earthworks measured noise near compressor and processing facilities in Pennsylvania, finding that levels were often in the upper 50-70 decibel (dBA) range, which exceeds state and federal standards.
When the Federal Energy Regulatory Commission (FERC) reviews interstate gas pipeline projects, compressor stations are included in the project plans. Under the federal Clean Air Act, state regulatory agencies also have to review plans for compressor stations and determine whether, based on projected pollution levels, they require just a state air permit or also require a federal one. State regulatory agencies must provide notice of when federal air permits (known as Title V) are open for public comment.