Forest Trail


32 results found for



Actions taken against a state or local government by the federal government for failure to plan or to implement a State Implementation Plan (SIP). Examples include withholding of highway funds and a ban on construction of new sources of potential pollution.

SB 25 (Children's Environmental Health Protection Act)

Changes to state law (Senate Bill 25, Escutia, 1999) established requirements for the ARB and the OEHHA to examine the impacts of air pollution on children's health. Specifically, the act required the state to evaluate all ambient air quality standards to determine whether these standards adequately protect human health, particularly that of infants and children; and, to identify toxic air contaminants that disproportionately impact children.

Scientific Review Panel (SRP)

Mandated by AB 1807, this nine-member panel advises the ARB, OEHHA and the California Department of Pesticide Regulation on the scientific adequacy of the risk assessment portion of reports issued by those three agencies in the process of identifying substances as toxic air contaminants. For more information, visit our SRP website.

Scoping Plan

AB 32 directed ARB to prepare a scoping plan for achieving the maximum technologically feasible and cost-effective reductions in greenhouse gas emissions by 2020. The scoping plan provides the outline for actions to reduce greenhouse gases in California. The approved scoping plan indicates how these emission reductions will be achieved from significant greenhouse gas sources via regulations, market mechanisms and other actions.


An air pollution control device that uses a high energy liquid spray to remove aerosol and gaseous pollutants from an air stream. The gases are removed either by absorption or chemical reaction.

Secondary Particle

Particles that are formed in the atmosphere. Secondary particles are products of the chemical reactions between gases, such as nitrates, sulfur oxides, ammonia and organic products.

Secondhand Smoke

Environmental tobacco smoke (ETS), or secondhand smoke, is a complex mixture of thousands of gases and fine particles emitted by the burning of tobacco products from the smoke exhaled by the smoker. Other minor contributors to ETS are from the smoke that is emitted from the smoldering end of the tobacco product and the vapor-phase related compounds that diffuse from the wrapper of the tobacco product.

Selective Catalytic Reduction (SCR) System

An emission control system that reduces NOx emissions through the catalytic reduction of NOx in diesel exhaust to N2 and H2O by injecting nitrogen-containing compounds into the exhaust stream, such as ammonia or urea.

Senate Bill 1731 (Calderon, 1993)

SB 1731 amended the Air Toxics "Hot Spots" Information and Assessment Act (AB 2588, "Hot Spots" or Program; 1987, Connelly) by adding two major elements. The first element required the OEHHA to adopt risk assessment guidelines for the program using a full public review process. These new risk assessment guidelines superseded the previous guidelines and include "supplemental" exposure information. Second, facilities determined to have a significant risk by the district, must conduct an airborne toxic risk reduction audit and develop a plan to implement airborne toxic risk reduction measures. The ARB is required to provide assistance to smaller businesses for developing and applying risk reduction techniques. As part of that assistance, the ARB developed guideline documents on how to conduct an audit, including a self-conducted checklist for certain industries.

Sensitive Groups

Identifiable subsets of the general population that are at greater risk than the general population to the toxic effects of a specific air pollutant (e.g., infants, asthmatics, elderly).


see Carbon Sequestration.

Shore Power

"Shore power", also known as Cold Ironing, refers to providing electrical power to a vessel that is docked. The purpose of shore power is to allow the vessel operator to turn off the vessel's auxiliary engines, which would normally be providing the necessary electricity. Although there are emissions associated with the generation of electricity used for shore power, those emissions are much less than those from the auxiliary engines, which burn diesel fuel.


A combination of smoke and other particulates, ozone, hydrocarbons, nitrogen oxides and other chemically reactive compounds which, under certain conditions of weather and sunlight, may result in a murky brown haze that causes adverse health effects. The primary source of smog in California is motor vehicles.

Smog Check Program

(See Inspection and Maintenance Program).

Smog Score

A score that ranks each vehicle's smog emissions on a scale of 1-10 (10 being the cleanest) relative to all other vehicles. All vehicles manufactured after January 1, 2009, must display this score on the Environmental Performance Label. For more information, visit our Drive Clean website.


A form of air pollution consisting primarily of particulate matter (i.e., particles released by combustion). Other components of smoke include gaseous air pollutants such as hydrocarbons, oxides of nitrogen and carbon monoxide. Sources of smoke may include fossil fuel combustion, agricultural burning and other combustion processes.

Solvent Base

Hydrocarbon-containing compounds such as paint thinner used for the purpose of thinning various types of coatings such as paint.


Very fine carbon particles that have a black appearance when emitted into the air.


Any place or object from which air pollutants are released. Sources that are fixed in space are stationary sources and sources that move are mobile sources.


Speciation is the analytical activity of identifying and/or measuring the quantities of one or more individual chemical species in a sample.

Spray Booth

A power ventilated structure enclosing a coating operation, to confine and limit the escape of spray, vapor and residue and to safely conduct or direct them to an exhaust system. The spray booth contains and captures particulate emissions and vents them to a control device.


Residents, environmentalists, businesses and government representatives that have a stake or concern about how air quality is managed.

State Implementation Plan (SIP)

A plan prepared by states and submitted to U.S. EPA describing how each area will attain and maintain national ambient air quality standards. SIPs include the technical foundation for understanding the air quality (e.g., emission inventories and air quality monitoring), control measures and strategies and enforcement mechanisms. (See also AQMP.) For more information, visit our SIP website.

Stationary Sources

Non-mobile sources such as power plants, refineries and manufacturing facilities which emit air pollutants.

Storage Tank

Any stationary container, reservoir, or tank, used for storage of liquids.


The layer of the Earth's atmosphere above the troposphere and below the mesosphere. It extends between 10 and 30 miles above the Earth's surface and contains the ozone layer in its lower portion. The stratospheric layer mixes relatively slowly; pollutants that enter it may remain for long periods of time.

Suggested Control Measure (SCM)

A model rule developed by air quality managers for local air districts to use to control the emissions from certain stationary sources of air pollution.


(See Sulfur Oxides.)

Sulfur Dioxide (SO2)

A strong smelling, colorless gas that is formed by the combustion of fossil fuels. Power plants, which may use coal or oil high in sulfur content, can be major sources of SO2 and other sulfur oxides contribute to the problem of acid deposition. SO2 is a criteria air pollutant.

Sulfur Hexafluoride (SF6)

SF6 is a colorless, non-toxic and non-flammable gas under standard conditions. It is used in many applications including as a gaseous dielectric medium in the electrical industry, an inert gas for the casting of magnesium, a tracer gas and an etchant in the semiconductor industry. SF6 is the most potent greenhouse gas with a global warming potential of 23,900 times that of carbon dioxide when compared over a 100-year period.

Sulfur Oxides

Pungent, colorless gases (sulfates are solids) formed primarily by the combustion of sulfur-containing fossil fuels, especially coal and oil. Considered major air pollutants, sulfur oxides may impact human health and damage vegetation.

Super Ultra Low Emission Vehicle (SULEV)

A vehicle that meets the ARB's super ultra-low emission vehicle standard of 0.03 grams per mile of NMOG+ NOx. See our Drive Clean website.