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Mendocino County Air Quality Management District Regulation 1 

RULE 1-130 - DEFINITIONS 

Except as otherwise specifically provided in these rules and regulations, words used in these rules 

and regulations are used in exactly the same sense as the same words are used in the federal Clean 

Air Act Amendments of 1990 and as amended at the time of application, Title 40 of the Code of 

Federal Regulations, Part 52.21, and Division 26 of the State of California Health and Safety Code. 

Where Title 40 of the Code of Federal Regulations, Part 52.21 refers to the responsibilities of the 

Administrator of the U.S. Environmental Protection Agency, the term Administrator shall be 

construed to mean Air Pollution Control Officer. 

[Amended 5/6/03, Amended 12/5/06, Amended 2/15/11] 

(a1) 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. 

(a2) 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. 

(a3) Air Pollution Abatement Operation: 

Any operation that has as its essential purpose a significant reduction in the emission of air 

contaminants or the effect of such emission. 

(a4) Air Pollution Control Officer (APCO): 

The Air Pollution Control Officer of the District 

(a5) Ambient Air Quality Standard: 

The specific concentrations and durations of air pollutants that reflect the relationship 

between intensity and composition of pollution to undesirable effects. 

(a6) Approved Combustibles: 

Brush, trees, and other vegetation grown on the property where it is to be burned. 

(b1) 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. (40 CFR 52.21(b)(13)) 
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Mendocino County Air Quality Management District Regulation 1 

(b2) Best Available Control Technology (BACT): 

An emissions limitation based on the maximum degree of reduction of each air contaminant 

subject to regulation under the federal Clean Air Act Amendments of 1990 and as amended at 

the time of application emitted from or that results from any stationary or portable source or 

modification, which the Air Pollution 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 that will exceed the emissions allowed under Rules 1-490 

and 1-492 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 (40 CFR 52.21(b)(12)). 

The BACT process shall be applied to any air contaminants that have been identified as toxic 

air contaminants (TAC) by the U.S. Environmental Protection Agency, the California Air 

Resources Board or the Mendocino County Air Quality Management District Board. 

[(b2) Paragraph 2 is not included as part of the SIP] 

(c1) CAAA: 

The Federal Clean Air Act Amendments of 1990, as amended at the time of application. 

(c2) CAPCOA: 

California Air Pollution Control Officer’s Association 

(c3) CCAA: 

California Clean Air Act 

(c4) CFR: 

Code of Federal Regulations 

(c5) Combustion Contaminants: 

Matter discharged into the atmosphere from the burning of any kind of material, excluding 

carbon dioxide and water. 

(c6) Compression Ignition (CI) 

Compression ignition internal combustion engine. 
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Mendocino County Air Quality Management District Regulation 1 

(c7) Control Strategy: 

A combination of measures designed to reduce air contaminant emissions in accordance with 

the State Implementation Plan for the Mendocino County Air Quality Management District. 

(d1) District: 

The Mendocino County Air Quality Management District as required by California Health 

and Safety Code, Section 40002 or a multi-county unified district authorized by Chapter 3, 

Part 3, Division 26, of said code. 

(d2) Dust: 

Minute solid particles released into the air by natural forces or by mechanical processes such 

as grading, crushing, grinding, milling, drilling, demolishing, shoveling, conveying, bagging, 

sweeping, etc. 

(e1) Emissions: 

The act of passing into the atmosphere an air contaminant or gas stream that contains an air 

contaminant, or the air contaminant so passed into the atmosphere. 

(e2) 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 that threatens the ambient air quality 

standard as defined in Rule 1-160 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. 

(f1) Fumes: 

"Fumes" means vapors, mists, and airborne liquid or solid particulate matter or any 

combination including these. 

(g1) Geothermal Operations: 

Those activities related to the extraction, transmission, and utilization of geothermal steam 

that may directly, or indirectly, result in air contaminant emissions. 

(g2) Greenhouse Gases (GHGs): 

A gas that has the capacity to create a warming effect in the earth’s atmosphere; for the 

purposes of this rule: carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), 

hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).

[Added 2/15/11] 
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Mendocino County Air Quality Management District Regulation 1 

(h1) Hearing Board: 

The appellate review board of the Mendocino County Air Quality Management District as 

provided for by Section 40800 of the California Health and Safety Code. 

(i1) Impact/Baseline Area: 

That area where the concentration of emissions from a proposed source is predicted to be 1 

ug/m3 or greater, using an Environmental Protection Agency approved ambient air quality 

model. 

(i2) Indirect Source: 

A facility, building, structure or installation, or combination thereof, that indirectly results in, 

or is projected to result in unmitigated emissions in excess of the following: ROG – 180 

lbs/day, NOx – 42 lbs/day, CO – 690 lbs/day, PM10 – 80 lbs/day. Projected unmitigated 

emissions are to be generated using the latest ARB approved version of URBEMIS with the 

Mountain and Rural Counties default settings, or other ARB approved indirect source model. 

In any model the latest available fleet, meteorology, and trip generation information will be 

used and the model run for each season. [Amended 5/6/03] 

(i3) 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. 

(l1) Large Grading Operation: 

A grading activity involving more than one (1) acre of exposed soil or more than one (1) mile 

of road during any single calendar year. 

[Added 12/5/06] 

(m1) Major Modification: 

“Major Modification” as it applies to gasoline dispensing facilities means the addition, 

replacement, or removal of an underground storage tank, underground piping, vapor piping 

within a dispenser, or a dispenser of an existing installation. The replacement of a dispenser 

is not a major modification when the replacement is occasioned by end user damage to a 

dispenser. 

(m2) Maximum Achievable Control Technology (MACT): 

An emissions limitation which is not less stringent than the emissions limitation achieved in 

practice by the best controlled similar source, and which reflects the maximum degree of 

reduction in emissions that the permitting authority, taking into consideration the cost of 

achieving such emission reduction, and any non-air quality health and environmental impacts 

and energy requirements, determines is achievable by the source. 
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Mendocino County Air Quality Management District Regulation 1 

(m3) Modeling: 

A procedure for estimating the ambient air concentration of air contaminants based upon 

emission profiles, dispersion simulations or other techniques approved by the U.S. 

Environmental Protection Agency, the California Air Resources Board and/or the Mendocino 

County Air Pollution Control Officer. 

(m4) Modification: 

"Modification" means any change in the structure, location, operation, conditions of 

operation, process materials or fuel of any stationary source that may increase or decrease the 

amount of any air contaminant emitted into the atmosphere by that source, and that is not 

already specifically allowed by a permit to operate issued by the District. An increase in 

production rate or in hours of operation beyond limits set in the permit to operate from the 

District is a modification. Otherwise, an increase or decrease in production rate or in hours of 

operation is not a modification. 

(n1) 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. 

(o1) 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. 

(o2) 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. 

(o3) Organic Gas: 

Any molecular gas containing carbon and hydrogen, or carbon and hydrogen in combination 

with any other element. 

(o4) Owner: 

Includes, but is not limited to, any person who leases, supervises or operates equipment, in 

addition to the normal meaning of ownership. 
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Mendocino County Air Quality Management District Regulation 1 

(p1) Particulate Matter: 

Any material, except uncombined water, that exists in a finely divided form as a liquid or 

solid at standard conditions. Specific size fractions of particulate matter are defined as 

follows: 

1. PM2.5 means particulate matter, both filterable and condensable, with an 

aerodynamic diameter less than or equal to a nominal two and one half (2.5) 

micrometers. 

2. PM10 means particulate matter, both filterable and condensable, with an 

aerodynamic diameter less than or equal to a nominal ten (10) micrometers. 

[Amended 2/15/11] 

(p2) Permit: 

Refers to either an Authority to Construct, Temporary Permit to Operate or Permit to Operate, 

whichever is legally in effect. 

(p3) Person or Persons: 

An individual, public or private corporation, political subdivision, agency, board, department 

or bureau of the state, municipality, partnership, co-partnership, firm, association, trust or 

estate, or any other legal entity whatsoever that is recognized in law as the subject of rights 

and duties. 

(p4) Portable Source: 

All units of air contaminant emitting articles, machines, equipment or other contrivance that 

are designed to be moved from location to location, whose emitting source is not the motive 

power for such moving, and that does not have a valid California Portable Equipment permit. 

(p5) 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. (40 CFR 52.21(b)(4)) 

(p6) PPM: 

Parts per million by volume expressed on a dry gas basis. 
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Mendocino County Air Quality Management District Regulation 1 

(p7) 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: 

Precursors Secondary Pollutants 

Volatile Organic Compounds 

 a) Photochemical oxidants (ozone O3) 

b) Organic fraction of PM10 

Nitrogen Oxides (NOx) a) Photochemical oxidants (Ozone) 

b) Nitrogen dioxide (NO2) 

c) Nitrates NO3 

d) Nitrate fraction of PM10 

e) Nitrate fraction of PM2.5 

Sulfur oxides (SOx) a) Sulfur dioxide (SO2) 

b) Sulfates (SO4) 

c) Sulfate fraction of PM10 

d) Sulfate fraction of PM2.5 

[Amended 2/15/11] 

(p7) 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 2 20 40 

 24-hour maximum* 5 91 182 

 3-hour maximum 25 512 700 

 

 Particulate Matter (PM 2.5) 

 Annual Arithmetic Mean 1 4 8 

 24-hour maximum* 2 9 18 

 

Particulate Matter PM-10 

 Annual Arithmetic Mean 4 17 34 

 24-hour maximum* 8 30 60 

 

Nitrogen Dioxide 

 Annual 

Arithmetic Mean

2.5 25 50 

* Not to be exceeded more than once a year. 
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Mendocino County Air Quality Management District Regulation 1 

(p7) Process Weight Per Hour: 

The total weight, including contained moisture of all materials introduced into any specific 

process which 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. 

(s1) 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 source to emit air contaminants that would equal or exceed 

any of the following rates, calculated on the basis of 24-hour emissions profiles, except as 

noted otherwise: 

Air Contaminant Significant Emissions Rate 

Carbon monoxide 550 lbs. per day 

Nitrogen oxides 220 lbs. per day 

Sulfur dioxide 220 lbs. per day 

Particulate matter 135 lbs. per day 

PM-10 80 lbs. per day 

PM2.5 54 lbs. per day of direct PM2.5 emissions; 

 220 lbs. per day of sulfur dioxide emissions; 

 220 lbs. per day of nitrogen oxide emissions. 

Ozone 220 lbs. per day of VOCs * or nitrogen oxides 

Lead 3 lbs. per day 

Asbestos .038 lbs. per day 

Beryllium .002 lbs. per day 

Mercury 0.5 lbs. per day 

Vinyl chloride 5.4 lbs. per day 

Fluorides 16 lbs. per day 

Sulfuric acid mist 38 lbs. per day 

Hydrogen sulfide (H2S) 54 lbs. per day 

Total reduced sulfur (including H2S) 54 lbs. per day 

Reduced sulfur compounds 

 (including H2S): .027 lbs. per day 

Municipal waste combustors: 

Organic emissions: 3.2 × 10-6 megagrams per year (3.5 × 10-6 tons 

per year) (measured as total tetra-through octachlorinated dibenzo-p-dioxins and 

dibenzofurans) 

Metals emissions: 14 megagrams per year (15 tons per year) 

(measured as particulate matter) 
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Mendocino County Air Quality Management District Regulation 1 

(s2) Significant (continued): 

Acid gas emissions: 36 megagrams per year (40 tons per year) 

(measured as sulfur dioxide and hydrogen 

chloride) 

Municipal solid waste landfills: 

Nonmethane organic compounds: 45 megagrams per year (50 tons per year) 

Greenhouse Gases: 

For the purpose of Rule 1-220 only: as specified in Rule 1-221.4 (a) or 1-221.4 (c) 

For the purpose of Regulation 5 only: as specified in Rule 1-221.4 (b) 

Other pollutants regulated under the Clean Air Act: any emissions rate whatsoever 

(52.21(b)(23)(ii)). 

Hazardous Air Pollutant (HAP) 

 listed pursuant to Section 112(g) 

 of the federal Clean Air Act 

 Amendments of 1990 and as 

 amended at the time of application 10 tons per year of any one HAP 

 25 tons per year for two or more HAPs 

* Volatile Organic Compounds except for ethanol sources below the EPA 

yearly threshold (40 tons per year). 

Not withstanding the above significant emissions rates for various air contaminants, 

significant also means any net emissions increase from any new or modified stationary source 

that 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). 

(40 CFR 52.21(b)(23)(iii)) The above Significant Emissions Rates are not to be used for 

CEQA determination. 

(s4) 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. 

(s5) 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). 

(s6) 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. 
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Mendocino County Air Quality Management District Regulation 1 

(s7) 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 Air Pollution 

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. 

(s8) Steam Generating Unit: 

Any furnace or boiler used in the process of burning fuel for the purpose of producing steam 

by heat transfer. 

(t1) 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 mists are not to be included in the 

determination of TRS. 

(t2) Toxic Air Contaminant: 

"Toxic air contaminant" means any substance identified by the Air Resources Board as a toxic 

air contaminant pursuant to California Health and Safety Code, Section 39650 et seq., or 

listed as a hazardous air pollutant pursuant to Subsection (b) of Section 112 of the federal 

Clean Air Act (42 U.S.C. Sec. 7412(b)). 

(t3) 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. 

(u1) URBEMIS: 

Urban Emissions Model. A CARB approved computer program that can be used to estimate 

emissions associated with land development projects in California such as residential 

neighborhoods, shopping centers, office buildings, and construction projects.