Pollutants of Interest

A brief description of the major particle and gaseous air contaminants that will be measured in AB 617 Community Air Monitoring program. This list is not exhaustive but will help better understand the specific monitoring methods, approaches and strategies

Pollutants of Interest

Particulate Matter (PM)

PM is comprised of a complex mixture of solid and/or liquid materials suspended in the air. Particles have different sizes, shapes, and chemical compositions. Based on their size, PM is generally categorized in three major categories:

  • PM10 (coarse PM): inhalable particles, with a diameter of 10 micrometers or smaller. These relatively large particles are generally mechanically generated by crushing or grinding operations;
  • PM2.5 (fine PM): fine inhalable particles, with a diameter of 2.5 micrometers or smaller. These particles are emitted from several sources such as traffic and industrial emissions or can be formed in the atmosphere through reaction of gaseous precursors;
  • Ultrafine particles (UFPs): very fine inhalable particles, with a diameter of 0.1 micrometers or smaller. UFPs are mostly emitted from fossil fuel combustion, particularly vehicular sources, or can be formed through photochemical reactions of gaseous precursors in the atmosphere. Unlike PM2.5 and PM10, which are measured by their mass concentration, UFPs are usually measured by the number of particles in a unit of air volume (i.e. number concentration).

Black Carbon (BC)

BC is a product of incomplete combustion of fossil fuels, biofuels, and biomass, and is emitted directly into the atmosphere in the PM2.5 size range (mostly). BC is a major component of “soot” from biomass burning, and a good indicator of diesel PM from heavy duty trucks and locomotives. Although often associated with emissions from heavy-duty diesel engines, a portion of all combustion emissions contains BC.

Nitrogen Oxides (NOx)

Both gasoline and diesel powered vehicles are the main sources of NOx emissions. However, substantial NOx emissions are also added into the atmosphere by stationary sources such as petroleum refineries and other industrial operations. NOx is a group of highly reactive gases that contribute to the formation of secondary particles, as well as tropospheric ozone. Scientific evidence links NO2 exposures with adverse respiratory effects. NO2 is one of the criteria pollutants, making it a compound that is routinely measured in ambient air monitoring networks. NO2 measurements also typically include measurement of NO, the other major NOx constituent.

Volatile Organic Compounds (VOCs) 

VOCs refers to a number (hundreds) of individual organic compounds which include non-methane hydrocarbons (NMHC) and oxygenated NHMC such as alcohols, aldehydes and organic acids. They are emitted by a wide variety of sources, and many hydrocarbons are associated with the use and production of fuels. Specifically, VOCs (mainly hydrocarbons) are typically emitted from refineries and related activities (e.g. crude oil production, storage tanks leaks, transport pipelines, others) but can also originate from other industrial activities. While measurements of NMHC can provide valuable information about potential refinery emissions, for a refinery it is possible to distinguish a few specific VOCs to represent fugitive emissions that have been associated with adverse health impacts (e.g. benzene, toluene, ethylbenzene, and xylenes; or BTEX). VOC emissions also occur from other combustion sources, such as wood combustion, and stationary and motor vehicle fossil fuel combustion, and elevated levels of BTEX compounds are expected in the vicinity of major roadways. This group of aromatic VOCs is important because not only they pose risk to human health, but they also play a role in formation of tropospheric ozone. Other VOC air toxics of concern that are often reported include 1,3-butadiene and styrene.

Hydrogen Sulfide (H2S)

Hydrogen sulfide is a colorless, flammable, extremely hazardous gas with a “rotten egg” smell. It can result from the breakdown of organic matter in the absence of oxygen such as in swamps and sewers, is emitted from chemical manufacturing and waste disposal, occurs naturally in crude petroleum and natural gas, and is produced at refineries as a by-product of crude oil processing. Low-level concentrations can occur continuously at petroleum refineries and its measurement will help identify potential leaks and address community odor concerns.

Other Pollutants and Air Toxics

In addition to the major air pollutants mentioned above there are other species that, although unlikely to be emitted in large quantities from the main source categories identified by the CSC, will also be monitored in this community if detected during our surveys. These are:

Particulate Metals

Metals can be emitted in trace amounts from a wide variety of anthropogenic sources such as combustion activities and facilities which conduct metal plating, forging, and heat treating. Of particular interest are nickel, mercury, copper, vanadium, lead, hexavalent chromium, and arsenic, because these species have been associated with adverse health effects in the urban environment. Measurement of metals usually involves analysis of PM filters collected over a defined time period (e.g. 24-hr) at a known sample volume. However, commercially available continuous multi-metals monitors are now available that can simultaneously measure the concentrations of several metals in hourly or sub-hourly time resolution.


Methane is a colorless and odorless gas, and is flammable in high concentrations (i.e. between 50,000 to 150,000 ppm). Methane is considered to be biologically inert, but can cause adverse health effects when levels are high enough to displace oxygen in the air, which can pose a suffocation hazard. However, this is generally only a concern in confined spaces rather than in typical outdoor and indoor environments where oxygen is readily available. Methane is not considered an air toxic and is not on the California Toxic Air Contaminants list, or in the California Proposition 65 list, or in the U.S. EPA Hazardous Air Pollutants list. Methane is well known greenhouse gas and is primarily regulated through state and federal laws.

Ammonia (NH3)

While the main sources of ammonia are natural, primarily from the decay of organic matter, petroleum refineries can also emit considerable amounts of this compound, particularly from catalyst regenerator vent releases. NH3 is colorless, pungent-smelling, and corrosive. Although it is unlikely to have adverse effect on health at background levels, exposure to high concentrations following an accidental release or in occupational settings may be harmful.

Sulfur Dioxide (SO2)

Heating and burning of fossil fuels containing sulfur release sulfur into the atmosphere, which in turn forms SO2 and other sulfur containing species. SO2 is classified as a criteria pollutant by the US EPA, can cause adverse health impacts if present in high concentrations in the ambient air, and can also cause damage to the environment.


Aldehydes emitted into ambient air include, but are not limited to, formaldehyde, acetaldehyde, and acrolein that are identified as toxic air contaminants (TAC) and could be emitted from a refinery. These compounds are the products of incomplete combustion of natural gas and are both precursors of atmospheric radicals that accelerate the formation of ozone and toxic air pollutants.

Carbonyl Sulfide (COS)

Carbonyl sulfide (COS) is naturally found in crude oil and is a chemical intermediate and a byproduct of oil refining with a distinct sulfide odor. It is classified as a California TAC and a federal hazardous air pollutant (HAP). COS can be released into atmosphere as fugitive emissions from refineries and at high concentration levels may cause narcotic-like effects in humans.

Hydrogen Cyanide (HCN)

Hydrogen cyanide is colorless, highly flammable and can be explosive when exposed to air in high concentrations. It is released from various industrial activities, including refining of crude oil. At high concentrations, such as those that may derive from accidental releases, it is highly toxic.

Hydrogen Fluoride (HF)

Hydrogen fluoride (HF) is a pungent, highly corrosive acid used at some oil refineries in a process called alkylation that boosts gasoline octane. HF also is used at chemical plants to manufacture compounds including refrigerants. This chemical poses a health risk to nearby residents and businesses because in the event of a large accidental release, it can form a dense, low cloud capable of causing severe damage to human skin and lung tissue.

You may also like ...

Newsletter Sign Up
Periodic newsletter updates via Email on a variety of air quality-related topics

South Coast Air Quality Management District

21865 Copley Dr, Diamond Bar, CA 91765



© 2019 South Coast Air Quality Management District