Air Quality Definitions
Acid precipitation or acid rain: Combination of water drops and elements with acidic qualities. Principal components typically include nitric and sulfuric acid with water vapor.
Ambient air: Ambient air is the outdoor air.
Annual arithmetic mean: The numerical average of the data for the year.
Air Quality Index (AQI): Index used to report daily air quality in areas.
Attainment: EPA designation that an area meets the National Ambient Air Quality Standards.
24-hour average: The average concentration for a 24-hour period.
CAA: Clean Air Act.
CAAA: Clean Air Act Amendments.
CAIR: Clear Air Interstate Rule.
CEM: Continuous Emissions Monitor.
CFR: Code of Federal Regulations.
Carbon Monoxide (CO): A colorless, odorless, very toxic gas resulting from incomplete combustion. CO can reduce the oxygen content of the blood. It also causes dizziness, headaches, blurred vision, and slowed reactions.
Criteria pollutant: An air pollutant for which certain levels of exposure have been determined to injure health, harm the environment and cause property damage. Criteria pollutants include PM10, PM2.5, SO2, NOx, VOCs and CO. The term "criteria pollutants" originated from the fact that standards are based on information published in air quality criteria documents.
Emissions: Air pollutants exhausted from a unit or source into the atmosphere.
Emission Inventory: An accounting of all air pollution emissions discharged into the atmosphere. An inventory contains the total emissions from sources within an area and over a specific time interval.
Exceedance: An incident occurring when the concentration of a pollutant in the ambient air is higher than the National Ambient Air Quality Standards.
EPA or U.S. EPA: Environmental Protection Agency
Fossil fuels: Natural gas, petroleum, coal or any form of solid, liquid or gaseous fuel derived from such material.
Hazardous Air Pollutants (HAPS): Chemicals or chemical classes widely considered to be toxic and that might cause adverse health effects. Currently there are 187 chemicals on the HAP list.
HP: Horsepower.
Lbs./hr.: Pounds per hour.
MACT: Maximum Achievable Control Technology.
Mercury: A naturally occurring element that is found in air, water and soil. It exists in several forms: elemental or metallic mercury, inorganic mercury compounds, and organic mercury compounds. Elemental or metallic mercury is a shiny, silver-white metal and is liquid at room temperature.
mmBtu/hr: Million British Thermal Units per Hour.
MSA: Metropolitan Statistical Area.
National Ambient Air Quality Standards (NAAQS): Allowable concentrations of air pollutants in the ambient air specified by the Federal Government. National Ambient Air Quality Standards, set by EPA to protect human health and welfare.
NESHAPS: National Emissions Standards for Hazardous Air Pollutants.
Nonattainment Area: An area which is shown by monitored data or by air quality modeling to exceed NAAQS for any pollutant.
Nonattainment: EPA designation that an area does not meet the National Ambient Air Quality Standards.
Nitrogen Oxides (NOx): Chemicals formed in high-temperature combustion processes. The substance is toxic and can react to form ozone or PM10 in the form of nitrates. Nitrogen dioxide (NO2) is brownish red gas with a biting odor. It is highly irritating in high concentrations. Nitrogen dioxide is always accompanied by nitric oxide (NO).
NSPS Source: Any stationary source of pollution for which the Administrator of EPA adopted a national standard that is published in 40 CFR Part 60, these categories of sources were established because it was determined the category contributed significantly to air pollution which may reasonably be anticipated to endanger public health or welfare.
O3: Ozone.
Ozone season: The period beginning May 1 and ending on September 30 of each year.
Pb: Lead.
Particulate Matter : "Particulate matter (PM)," also known as particle pollution, is a complex mixture of extremely small dust and soot particles. Particle pollution is divided into two categories, “PM10” and “PM2.5.” PM10 is matter less than 10 micrometers in diameter. That would be about one-seventh the width of a strand of human hair. PM2.5 is even smaller - measuring 2.5 micrometers or less.
ppb: Parts per billion by volume.
ppm: Parts per million by volume.
Precursor: A substance that is the source of or aids in the formation of another substance.
PSD: Prevention of Significant Deterioration.
Regulated air pollutant: Any air pollutant subject to a standard or other requirement promulgated under section 112 of the Clean Air Act or any air pollutant for which a National Ambient Air Quality Standard has been promulgated including particulate matter, sulfur dioxide, carbon monoxide, nitrogen dioxide, ozone and lead or lead compounds.
Secondary Pollutants: Chemicals that are not emitted directly from sources into the atmosphere, but formed through complex chemical reactions of precursor species. Ozone, sulfates and nitrates (the last two being types of PM2.5) are examples of secondary air pollutants.
SIC: Standard Industrial Classification.
State Implementation Plans (SIP)s: Long range plans required by EPA and implemented by state or local agencies to attain NAAQS.
Sulfur Oxides (SO2): An invisible gas with a pungent odor. At low concentrations, this gas can often be tasted before smelled. The major source of sulfur oxides is the combustion of sulfur-containing fuels, primarily coal and fuel oil. Sulfur dioxide is a toxic substance that can impair breathing.
Source or stationary source: Any governmental, institutional, commercial or industrial structure, installation, plant, building or facility that emits or has the potential to emit any regulated air pollutant under the Clean Air Act.
Statutory Air Pollution: The discharge into the air by the act of man of substances (liquid, solid, gaseous, organic or inorganic) in a locality, manner and amount as to be injurious to human health or welfare, animal or plant life, or property, or which would interfere with the enjoyment of life or property.
TPY: Tons per Year.
Volatile Organic Compounds (VOC): Any compound of carbon (other than carbon monoxide, carbon dioxide, carbonic acid, metallic carbonates, metallic carbides and ammonium carbonate) which participates in atmospheric photochemical reactions. A company must report all reactive VOC emissions (including fugitive emissions). VOC emissions which are non-reactive are not reported.