Forest Trail


19 results found for


Major Source

A stationary facility that emits a regulated pollutant in an amount exceeding the threshold level depending on the location of the facility and attainment with regard to air quality status. (See Source.)

Market-Based Approaches

A system of market-based declining annual aggregate emissions limitations for sources, or categories of sources, that emit greenhouse gases. Market-based can also refer to greenhouse gas emissions exchanges, banking, credits and other transactions, governed by rules and protocols established by the ARB, that result in the same greenhouse gas emission reduction, over the same time period, as direct compliance with a greenhouse gas emission limit or emission reduction measure adopted by the ARB.

Maximum Achievable Control Technology (MACT)

Federal emissions limitations based on the best demonstrated control technology or practices in similar sources to be applied to major sources emitting one or more federal hazardous air pollutants. For more information, visit our Title III website.

Maximum Incremental Reactivity (MIR)

A measure of the increase in ozone formation per unit weight of a hydrocarbon when added to the atmosphere.




The middle value in a population distribution, above and below which lie an equal number of individual values; midpoint.

Melting Point

The temperature at which a solid becomes a liquid. At this temperature, the solid and the liquid have the same vapor pressure.


The layer of the Earth's atmosphere above the stratosphere and below the thermosphere. It is between 35 and 60 miles from the Earth.

Methyl Tertiary Butyl Ether (MTBE)

An ether compound added to gasoline to provide oxygen and enhance complete combustion. MTBE has been phased out of California's gasoline. See our fuels website, for more information.

Military Personnel

Active duty members of the U.S. armed forces or reserves assigned to California facilities and active duty.


Capable of being mixed with other substances.


Million metric tons of carbon dioxide equivalents.

Mobile Sources

Sources of air pollution such as automobiles, motorcycles, trucks, off-road vehicles, boats and airplanes. (See also stationary sources.) For more information, please go to our mobile sources portal page.


The periodic or continuous sampling and analysis of air pollutants in ambient air or from individual pollution sources.


Rate of disease incidence.


Death rate.

Motor Vehicle Fee Program

See AB 2766.

Multimedia Exposure

Exposure to a toxic substance from multiple pathways such as air, water, soil, food and breast milk.


The ability of a chemical or physical agent to produce heritable changes in the DNA of living cells.