Except as otherwise specifically provided in these rules and regulations, and except where the context indicates otherwise, words used in these rules and regulations are used in exactly the same sense as the same words are used in the Health and Safety Code of the State of California, the Clean Air Act of 1977, and the Code of Federal Regulations 40 CFR 52.21 (August 7, 1980). Where the federal regulations of 40 CFR 52.21 refer to the responsibilities of the administrator of the U.S. Environmental Protection Agency, the term Administrator shall be construed to mean Control Officer.

AGRICULTURAL OPERATION: The growing and harvesting of crops, or the raising of fowl, animals or bees as a gainful occupation, or forest management, or range improvement or in the improvement of land for wildlife and game habitat, or disease or pest prevention.

AIR CONTAMINANT: Any discharge, release, or other propagation into the atmosphere directly, or indirectly, caused by man and includes, but is not limited to, smoke, charred paper, dust, soot, grime, carbon, fumes, gases, odors, particulate matter, acid, or any combination thereof.

AIR POLLUTION ABATEMENT OPERATION: Any operation which has as its essential purpose a significant reduction in the emission of air contaminants or the effect of such emission.

AMBIENT AIR QUALITY STANDARD: The specific concentrations and durations of air pollutants which reflect the relationship between intensity and composition of pollution to undesirable effects.

APPROVED COMBUSTIBLES: Paper, cardboard, brush, trees, native vegetation or other materials as approved by the Control Officer.

BASELINE CONCENTRATION: That ambient concentration level which exists in the baseline area at the time of the establishment of the applicable baseline date as determined in accordance with Section 52.21 of the Code of Federal Regulations. (52.21(b)(13))

BASE UNIT: Any major emitting device, process line, or other equipment or grouping thereof, that emits, or has the potential to emit, regulated air pollutants; for the purposes of this rule, the term base unit shall include, but shall not be limited to, any of the following:

  1. any major emitting device or process line, or
  2. any aggregate production line, including a primary crusher and associated crushers, screens, conveyors, stackers, and piles, or
  3. any cement batch plant, or
  4. any asphalt hot mix plant, or
  5. any debarker and head rig, or
  6. any rip and gangsaw line, or
  7. any planing operation, or
  8. any cooling tower, or
  9. any vent gas treatment system, or
  10. any burner/scrubber system, or
  11. any stretford system, or
  12. any geothermal production, injection, observation, or idle steam well and geothermal steam transmission system, or aggregation thereof, that provide steam to - or are included in the steamfield of a single or dual-unit geothermal electrical power generation plant, or
  13. any onsite combustion device used for power or process heat generation, except for emergency standby generators or any device that is covered under another base unit definition in this rule.
  14. any geothermal well drilling operation, or aggregation thereof, conducted on a company's leasehold.

BEST AVAILABLE CONTROL TECHNOLOGY (BACT): An emission limitation based on the maximum degree of reduction of each air contaminant subject to regulation under the Clean Air Act of 1977 emitted from or which results from any stationary source or modification, which the Control Officer,on a case by case basis, taking into account energy, environmental, and economic impacts and other costs, determines is achievable for such stationary source through application of production processes and available methods, systems, and techniques for control of such air contaminants. Said BACT determinations may include a design standard, operational equipment specifications, fuel restrictions, work practice or combination thereof. In no event shall application of BACT result in emissions of any pollutants which will exceed the emissions allowed under Rules 490 and 492 of this regulation. If the reviewing authority determines that technological or economic limitations on the application of measurement methodology to a particular emissions unit would make the imposition of an emissions standard infeasible, a design, equipment, work practice, operational standard or combination thereof, may be prescribed instead to satisfy the requirements for the application of BACT.(52.21(b)(12))

COMBUSTION CONTAMINANTS: Matter discharged into the atmosphere from the burning of any kind of material, excluding carbon dioxide and water.

CONTROL OFFICER: The Air Pollution Control Officer of the District

CONTROL STRATEGY: A combination of measures designed to reduce air contaminant emissions in accordance with the State Implementation Plan for the California North Coast Air Basin.

DISTRICT: The County Air Pollution Control District as required y Section 40002 of the California Health and Safety Code or a multi- county unified district authorized by Chapter 3, Part 3, Division 26 of said code.

DUST: Minute solid particles released into the air by natural forces or by mechanical processes such as crushing, grinding, milling, drilling, demolishing, shoveling, conveying, bagging, sweeping, etc

EMISSION: The act of passing into the atmosphere an air contaminant or gas stream which contains an air contaminant, or the air contaminant so passed into the atmosphere.

EPISODE ALERT: A condition in an air basin whenever the concentration of any air contaminant in that air basin has been verified to have reached a predetermined level which threatens the ambient air quality standard as defined in Rule 160 depending upon the particular topography and meteorology of the air basin. "Verified" means the pertinent measuring instrument has been checked over the following fifteen-minute period and found to be operating correctly.

GEOTHERMAL OPERATIONS: Those activities related to the extraction, transmission, and utilization of geothermal steam which may directly, or indirectly, result in air contaminant emissions.

HEARING BOARD: The appellate review board of the District as provided for by Section 40800 of the California Health and Safety Code.

INDIRECT SOURCE: A facility, building, structure or installation, or combination thereof, which indirectly results in emissions of an air contaminant as a result of traffic greater than 20,000 or more vehicles per day within 10 years of construction; any new or modified facility which provides in excess of 1,000 new parking spaces; or any new or modified airport with more than 50,000 operations per year by regularly scheduled air carriers, or used by 1,600,000 or more passengers per year.

INSTALLATION: The placement, assemblage or construction of equipment or control apparatus at the premises where the equipment or control apparatus will be used, and includes all preparatory work at such premises

KRAFT PULP MILL: Any industrial operation which uses for a cooking liquor an alkaline sulfide solution containing sodium sulfide in its pulping process.

KRAFT PULP-MILL NON-CONDENSIBLES: The TRS portion of any gases and vapors released in a kraft pulp mill from the digester flash steam condensers, blow tanks, multiple effect evaporator vacuum seal tanks, multiple effect evaporator condensers, and condensate strippers.

KRAFT PULP MILL PRODUCTION: Tons of air-dried unbleached kraft pulp produced by a kraft pulp mill, or equivalent. A value equal to 50 percent of the weight of dry wood charged into the kraft cooking process may be substituted for those mills where a value of air-dried unbleached kraft pulp is not readily obtainable.

KRAFT RECOVERY FURNACE: The combustion device in which pulping chemicals are converted to a molten smelt and wood solids are incinerated. For these regulations, and where present, this term shall include the direct contact evaporator.

LIME KILN: Any production device in which calcium carbonate is thermally converted to calcium oxide.

MODELING: A procedure for estimating the ambient air concentration of air contaminants based upon emission profiles, dispersion simulations or other techniques approved by the Environmental Protection Agency, California Air Resources Board and the Control Officer. (52.21(l))

MODIFICATION: Any physical change in, or in the method of operation of any stationary source which increases the amount of any air contaminant emitted into the atmosphere by that source.

NET INCREASE IN EMISSIONS: The amount by which the sum of any increase in actual emissions from a particular physical change or change in method of operation at a stationary source, and any other increases and decreases in actual emissions at the source that are creditable in accordance with 40 CFR 52.21(b)(3) and (21), exceeds zero.

OPERATION: Any physical action resulting in a change in the location, form or physical properties of a material, or any chemical action resulting in a change in the chemical composition or the chemical or physical properties of a material.

ORCHARD,VINEYARD, OR CITRUS GROVE HEATER: Any article, machine, equipment or other contrivance, burning any type of fuel or material capable of emitting air contaminants, used or capable of being used for the purpose of giving protection from frost damage.

ORGANIC GAS: Any gas containing carbon and hydrogen, or carbon and hydrogen in combination with any other element.

OTHER KRAFT MILL SOURCES: Sources of TRS emissions in a kraft mill other than recovery furnaces and lime kilns, including but not limited to: vents from knotters, brown stock washers, smelt tanks, black liquor oxidation systems, tall oil recovery operations, and any other vent which contributes over 1 percent of the total kraft mill TRS emissions.

OWNER: Includes, but is not limited to, any person who leases, supervises or operates equipment, in addition to the normal meaning of ownership.

PARTICULATE MATTER: Any material, except uncombined water, which exists in a finely divided form as a liquid or solid at standard conditions.

PERMIT: Refers to either an authority to construct, temporary permit to operate or permit to operate, whichever is legally in effect. For purposes of prevention of significant deterioration enforceability, the permit to operate will be considered a modified authority to construct.

PERSON OR PERSONS: An individual, public or private corporation, political subdivision, agency, board, department or bureau of the state, municipality, partnership, copartnership, firm, association, trust or estate, or any other legal entity whatsoever which is recognized in law as the subject of rights and duties.

POTENTIAL TO EMIT: The maximum capacity of a stationary source to emit an air contaminant under its physical and operational design, after considering physical and operational limitations that are enforceable by conditions imposed by the district in both the Authority to Construct and Permit to Operate. (52.21(b)(4))

PPM: Parts per million by volume expressed on a dry gas basis.

PRECURSOR: A substance that, when released to the atmosphere, forms or causes to be formed or contributes to the formation of another or secondary air pollutant for which a national ambient air quality standard has been adopted, or whose presence in the atmosphere will contribute to the violation of one or more national ambient air quality standards. Presently identified precursors and secondary pollutants are:

 Volatile Organic Compounds  Organic fraction of PM10
 Nitrogen Oxides (NOx)  Nitrogen dioxide (NO2)
   Nitrate fraction of PM10
 Sulfur Oxides (SOx)  Sulfur dioxide (SO2)
   Sulfates (SO4)
  Sulfate fraction of PM10

PREVENTION OF SIGNIFICANT DETERIORATION (PSD) INCREMENT: The maximum allowable increase of ambient air quality above baseline concentration in the three classified areas.

Allowable PSD Increments
micrograms per cubic meter


Class I

Class II

Class III

 Sulfur Dioxide




   annual arithmetic mean




   24-hour maximum*




   3-hour maximum*




 Total Suspended Particulate




   annual geometric mean




  24-hour maximum* 




 Nitrogen Dioxide




   Annual average




 * Not to be exceeded more than once a year.

PROCESS WEIGHT PER HOUR: The total weight, including contained moisture of all materials introduced into any specific process which process may cause any discharge into the atmosphere. Solid fuels charged will be considered as part of the process weight, but liquid and gaseous fuels and combustion air will not. The "process weight per hour" will be derived by dividing the total process weight by the number of hours in one complete operation from the beginning of any given process to the completion thereof, excluding any time during which the equipment is idle. For continuous processes, the average hourly total weight of materials introduced into the process will be used in calculations.

SECTION: Refers to a section of the Health and Safety Code of the State of California unless some other statute is specifically mentioned.

(s2) SIGNIFICANT: The potential of a new or modified stationary source to emit air contaminants that would equal or exceed any of the following rates: (52.21 (b)(23)(i))
Air Contaminant

Significant Emission Rate


tons per year

Carbon monoxide

100 tons per year (tpy)

Nitrogen oxides

40 tpy

Sulfur dioxide

40 tpy

Particulate matter

25 tpy


15 tpy


40 tpy (of volatile organic compounds)


0.6 tpy


0.007 tpy


0.0004 tpy


0.1 tpy

Vinyl chloride

1 tpy


3 tpy

Sulfuric acid mist

7 tpy

Hydrogen sulfide (H S)

10 tpy

Total reduced sulfur (including H S)

10 tpy

Reduced sulfur compounds (including H S)

10 tpy


Other pollutants regulated under the Clean Air Act of 1977

any emissions rate whatsoever
(52.21 (b) (23) (ii))

Not withstanding the above significant emission rates for various air contaminants, significant also means any net emission increase from any new or modified stationary source which would be constructed within 10 kilometers of a Class I area and have an air quality impact on such area equal to or greater than 1 microgram per cubic meter (24 hour average).(52.21(b)(23)(iii))


(1) Any business activity in agriculture, general construction, special trade construction, retail trade, wholesale trade, services, transportation and warehousing, manufacturing, generation and transmission of electric power, or a health care facility, unless excluded in paragraph (2), that is both of the following:

    1. Independently owned and operated, and
    2. Not dominant in its field of operation.

(2) "Small business" does not include the following professional business activities:

  1. A financial institution or bank, a trust, a savings and loan association, a thrift institution, a consumer finance company, a commercial finance company, an industrial finance company, a credit union, a mortgage and investment banker, a securities broker-dealer, or an investment adviser.
  2. An insurance company, either stock or mutual.
  3. A mineral, oil, or gas broker; a subdivider or developer.
  4. A landscape architect, an architect, or a building designer.
  5. An entity organized as a nonprofit institution.
  6. An entertainment activity or production, including a motion picture, a stage performance, a television or radio station, or a production company.
  7. A utility, a water company, or a power transmission company generating and transmitting more than 4.5 million kilowatt hours annually.
  8. A petroleum producer, a natural gas producer, a refiner, or a pipeline.
  9. A business activity exceeding the following annual gross receipts in the categories of:
    1. Agriculture, one million dollars ($1,000,000).
    2. General construction, nine million five hundred thousand dollars ($9,500,000).
    3. Special trade construction, five million dollars ($5,000,000).
    4. Retail trade, two million dollars ($2,000,000).
    5. Wholesale trade, nine million five hundred thousand dollars ($9,500,000).
    6. Services, two million dollars ($2,000,000).
    7. Transportation and warehousing, one million five hundred thousand dollars ($1,500,000).
  10. A manufacturing enterprise exceeding 250 employees.
  11. A health care facility exceeding 150 beds or one million five hundred thousand dollars ($1,500,000) in annual gross receipts.

Ref: State Government Code § 11342(h)

SMELT DISSOLVING TANK: A vessel used for dissolving the molten salts (smelt) recovered from the kraft recovery furnace.

STACKING: The venting of geothermal steam from associated unit steam supply transmission line into the atmosphere during associated power plant shutdowns (outages), startups or load curtailments.

STANDARD CONDITIONS: As used in these regulations, refers to a gas temperature of 20 degrees Centigrade (68 degrees Fahrenheit) and a gas pressure of 760 millimeters of mercury absolute (14.7 pounds per square inch absolute).

STANDARD CUBIC METER OF GAS (STANDARD CUBIC FOOT OF GAS): The amount of gas that would occupy the specified cubic measure, if free of combined water, at standard conditions.

STATIONARY SOURCE: All units of air contaminant emitting articles, machines, equipment or other contrivances, which are located on adjacent or contiguous properties under the control of the same person (or persons under common control) and all of which are determined by the Control Officer to be related to one another through a similar product, raw material or function and are included in the same standard industrial classification.

STEAM GENERATING UNIT: Any furnace or boiler used in the process of burning fuel for the purpose of producing steam by heat transfer.

TOTAL REDUCED SULFUR (TRS): "TRS" means total reduced sulfur contained in hydrogen sulfide, mercaptans, dimethyl sulfide, dimethyl disulfide or other organic sulfide compounds, all expressed as hydrogen sulfide. Sulfur dioxide, sulfur trioxide, or sulfuric acid mist are not to be included in the determination of TRS.

TOXIC AIR CONTAMINANT (TAC): A toxic air contaminant (TAC) is any substance identified by the Air Resources Board as a toxic air contaminant pursuant to California Health and Safety Code Section 39650 et. seq.

TRADE SECRETS: As used in these rules and regulations, Trade Secrets include, but are not limited to, any formula, pattern, process, tool, mechanism, compound, procedure, production data, or compilation of information which is not patented, which is known only to certain individuals within a commercial concern who are using it to fabricate, produce, or compound an article of trade or to perform a service having commercial value, and which gives its user an opportunity to obtain a business advantage over competitors who do not know or use it.