Continuous Emissions Monitors (CEMs)

Pollutants which can be
continuously monitored (partial list)

Particulate Matter
Carbon Monoxide (CO)
Carbon Dioxide (CO2)
Nitrogen Oxides (NOx)
Nitrous Oxide (N2O)
Sulfur Oxides (SOx)
Hydrogen Sulfide (H2S)
Hydrofluoric Acid (HF)
Hydrochloric Acid (HCl)
Hydrogen Cyanide
Volatile Organic Compounds (VOCs)
Methane
Ethylene
Acetylene
Methanol
Antimony
Arsenic
Barium
Bromine
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Nickel
Selenium
Silver
Thallium
Tin
Titanium
Vanadium
Zinc
Ammonia
Dioxins & furans
Polycyclic Aromatic Hydrocarbons (PAHs)
Vinyl Chloride Monomer

Most industrial facilities with combustion systems (incinerators, power plants, refineries, etc.) are not required to regularly test for most of the chemical pollutants they release. Facility operators will draw attention to the fact that they have continuous emissions monitors (CEMs) and that engineers in a control room are constantly paying attention to their emissions, making sure they're within legal limits.

Typically, only a few pollutants are tested in this way, though... usually Nitrogen Oxides (NOx), Carbon Monoxide (CO) and Sulfur Dioxides (SO2). Oxygen and various operating parameters like temperature are also typically monitored on a continuous basis. Sometimes continuous monitoring is required for opacity (an indirect way to measure particulate matter), hydrochloric acid or, more recently, mercury or particulate matter.

The most toxic pollutants are typically tested only yearly, if at all. Such infrequent testing (under ideal operating conditions) allows for easy manipulation of test results and is known to underestimate real emissions (see the Dioxin CEMs page for docmentation).

Currently, the technology exists to continually monitor a long list of pollutants, including toxic metals, acid gases, dioxins, particulate matter and more (see box on right).

Any corporation that claims that their facility's emissions will be within certain limits should be put to the test by asking that they install CEMs to provide real-time emissions data to back up their claims. All CEM data ought to be made available real-time on a publicly-available Internet website, as a condition of state permits. Where state agencies are unwilling to require such disclosure, local governments ought to pass laws to provide such requirements, as has been done with local ordinances in Pennsylvania.

CEM Equipment Verification:

Vendors providing CEM equipment:

International Conferences on Emission Monitoring:


Dioxin CEMs:

Proposed facilities required to use CEMs for Mercury: