(Adopted: 11/04/77; Amended: 09/01/78; Amended: 02/02/79;

Amended 01/08/82; Amended: 05/06/83; Amended 05/04/90; 

Amended: 04/05/91; Amended: 09/11/92; Amended: 10/02/92; 

Amended: 11/17/95; Amended: 08/21/12) 

AVAQMD Rule 431.1 431.1-1

Sulfur Content of Gaseous Fuels 

RULE 431.1 

Sulfur Content of Gaseous Fuels 

(A) General 

(1) Purpose 

(a) The purpose of this rule is to reduce sulfur oxides (SOx) emissions from 

the burning of gaseous fuels in stationary equipment. 

(2) Applicability 

(a) The provisions of this rule shall apply to any burning, transferring, selling 

or the offering for sale of any gaseous fuels containing sulfur compounds 

in excess of 16 parts per million by volume (ppmv), calculated as 

hydrogen sulfide (H2S), in stationary equipment requiring a Permit to 

Operate (PTO) by the Antelope Valley Air Quality Management District 

(District). 

(B) Definitions 

(1) “Air Pollution Control Officer” (APCO) – The person appointed to the position of 

Air Pollution Control Officer of the District pursuant to the provisions of 

California Health & Safety Code §40750, and his or her designee. 

(2) “Authority to Construct Permit” (ATC) – A District permit required pursuant to 

the provisions of District Rule 201 which must be obtained prior to the building, 

erecting, installation, alteration or replacement of any Permit Unit. Such permit 

may act as a temporary PTO pursuant to the provisions of District Rule 202.

(3) Burn – To combust any gaseous fuel, whether for useful heat or by incineration 

without heat recovery, except for flaring of emergency vent gases. 

(4) “California Air Resources Board” (CARB) – The California State Air Resources 

Board the powers and duties of which are described in Part 2 of Division 26 of the 

California Health & Safety Code (commencing with section 39500).

(5) Continuous Emission Monitoring System (CEMS) – A system of equipment that 

continuously measures and records all parameters necessary to directly determine 
AVAQMD Rule 431.1

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431.1-2

concentrations and/or mass emissions of selected pollutants, and which meets all 

of the requirements of Attachment A, Section II. 

(6) Continuous Fuel Gas Monitoring System” (CFGMS) – A system of equipment 

that continuously measures and records total sulfur concentration in the gaseous 

fuel prior to burning, and which meets all the requirements of Attachment A, 

Section I. 

(7) “Continuous Monitor” – a CEMS or CFGMS. 

(8) Daily Average – An arithmetic mean of all of a facility’s sulfur compounds 

readings within a calendar day obtained according to the guideline specified in 

Attachment A. 

(9) “District” – The Antelope Valley Air Quality Management District, the 

geographical area of which is described in District Rule 103. 

(10) Emergency Vent Gas – Any gas released from a process unit as a result of any 

process upset or breakdown. 

(11) Gaseous Fuel – Any gaseous material which releases heat when burned including, 

but not limited to, any natural, refinery, field produced, process, synthetic, landfill, 

sewage digester, or waste gases with a gross heating value of 2670 kilocalories per 

cubic meter (300 BTU per cubic foot) or higher, at standard conditions. 

(12) Landfill Gas – Any gas derived through any biological process from the 

decomposition of organic waste buried within a waste disposal site. 

(13) Monthly Weighted Average Sulfur Content – The result of the summation of 

average daily sulfur contents of the fuel(s) consumed multiplied by the average 

daily consumption rates of the fuel(s) consumed in any month divided by the total 

gaseous fuel consumption rate for that month. 

(14) Natural Gas – A mixture of gaseous hydrocarbons, with at least 80 percent 

methane (by volume), and of pipeline quality, such as the gas sold or distributed 

by any utility company regulated by the California Public Utilities Commission. 

(15) “Permit to Operate” (PTO) – A District permit required pursuant to the provisions 

of District Rule 203 which must be obtained prior to operation of a Permit Unit. 

An ATC may function as a temporary PTO pursuant to the provisions of District 

Rule 202. 

(16) Refinery Gas – Any combustible gaseous by-product generated from a petroleum 

refinery process unit operation, with a gross heating value of 2670 kilocalories per 

cubic meter (300 BTU per cubic foot) or higher, at standard conditions. 
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(17) Sewage Digester Gas – Any gas derived from anaerobic decomposition of organic 

sewage within its containment. 

(18) “South Coast Air Quality Management District” – The air quality district created 

pursuant to Division 26, Part 3, Chapter 5.5 of the California Health & Safety 

Code (commencing with §40400). 

(19) Standard Conditions – The atmospheric state where the temperature is 60°F and 

barometric pressure is 14.7 pounds per square inch absolute. 

(20) Stream Day – Any day or part of a day when a facility or a process unit is in 

operation. 

(21) “United States Environmental Protection Agency” (USEPA) - The United States 

Environmental Protection Agency, the Administrator of the USEPA and his or her 

authorized representative. 

(C) Requirements 

(1) Natural gas 

A person shall not sell or offer for sale for use in the jurisdiction of the District 

natural gas containing sulfur compounds, calculated as H2S, in excess of 16 parts 

per million by volume (ppmv). 

(2) Other Gaseous Fuels 

A person shall not burn in equipment requiring a PTO, purchase, transfer, sell or 

offer for sale for use in the jurisdiction of the District, any gaseous fuel containing 

sulfur compounds, calculated asH2S, in excess of the concentration limits as 

measured over the averaging periods for various gaseous fuels as specified in 

Table 1.

TABLE 1 

Fuel Type Sulfur Limits ppmv Averaging Periods 

Refinery Gas 40 4 hrs 

Landfill Gas 250 Daily 

Sewage Digester Gas 40 or Daily or 

 40 and 500 Monthly and 15-minutes 

Other Gases 40 4 hrs 
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(3) Previously Exempt or Previously Compliant Facilities 

A person burning gaseous fuel containing sulfur compounds in excess of the 

limits specified in Table 1 and whose facility had been previously exempt from 

this rule pursuant to subsection (G)(6); or any person who, without the use of any 

sulfur removal or control system, had been previously in compliance with the 

limits specified in Table 1, shall: 

(a) Submit for approval by the APCO within 30 days from the time of 

exceedance or non-compliance, a plan to demonstrate compliance with the 

requirements of the rule; 

(b) Submit to the APCO an application for a fuel gas control system within six 

months of the time of exceedance of the exemption criteria specified in 

subsection (G)(6), or non-compliance with the limit; 

(c) Demonstrate compliance with the limit specified in Table 1 no later than 

18 months after the time of exceedance; and 

(d) Comply with subsections (D)(1) and (D)(2), or (D)(3). 

(D) Monitoring Requirements 

(1) Except as provided in subsection (D)(3), a person burning gaseous fuels, other 

than exclusively natural gas, in stationary equipment requiring a PTO by the 

District shall have a properly operating continuous fuel gas monitoring system 

(CFGMS) to determine the sulfur content, calculated as H2S, of the fuel gas prior 

to burning, or a continuous emission monitoring system (CEMS) to determine 

SOx emissions after burning. All continuous monitors, require District approval, 

which shall be based on the requirements as specified in Attachment A. 

(a) A person shall install the CFGMS upstream of any mixing of refinery 

gases with natural gas, propane or other fuels. 

(b) A person subject to subsection (C)(3) of this rule shall comply with 

subsections (D)(1) and (D)(2) no later than twelve months after the date an 

ATC is issued by the District for a sulfur removal system or comply with 

subsection (D)(3). 

(c) Compliance with the Table 1 sulfur limits shall be determined based on 

readings obtained from an approved Continuous Monitor. 

(2) A person installing a Continuous Monitor shall submit to the District for approval, 

a quality assurance procedure as specified in USEPA 40 CFR Part 60, Appendix 

F, Procedure 1 for CEMS and, as applicable, for CFGMS. 
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431.1-5

(a) The quality assurance procedure specified above shall be submitted to the 

District for written approval by the APCO prior to the CFGMS or CEMS 

final certification. 

(b) Any CFGMS or CEMS deemed to be out of control, as specified in 

Attachment A, according to the facility quality assurance procedure 

approved by the APCO shall be corrected within 72 hours. 

(i) The person operating the CFGMS or CEMS shall notify the APCO 

by telephone or facsimile of any breakdown(s) of the monitoring 

systems if the duration of the breakdown is in excess of 60 minutes 

or if there are three (3) or more breakdowns in any one day within 

24 hours of the occurrence of the breakdown which triggers 

notification. Such report shall identify the time, location, 

equipment involved, and contact person. 

(ii) The person who complies with the provisions of subsection 

(D)(2)(b)(i) and subsection (E) (3) shall not be considered in 

violation of this rule for the 72 hour period of breakdown provided 

that the breakdown did not result from operator error, neglect or 

improper operation or maintenance procedures. 

(3) A person burning landfill gas or sewage digester gas, or who is subject to 

subsection (C)(3) of this rule may use an alternative monitoring method, in lieu of 

the requirements in subsections (D)(1) and (D)(2), that ensures compliance with 

the daily total sulfur content limitation as specified in Table 1. Alternative 

monitoring methods shall not be used unless first approved in writing by the 

APCO, the California Air Resources Board (CARB), and the Regional 

Administrator of the Environmental Protection Agency (EPA), Region IX, or their 

designees. 

(a) At a minimum, the alternative monitoring method shall meet the 

guidelines of Attachment A, Section III. 

(b) A person subject to subsection (C)(3) of this rule shall submit an 

alternative monitoring method for approval no later than 45 days after the 

date an ATC for a sulfur removal system is issued. 

(c) All monitoring must comply with the approved alternative monitoring 

method. 

(d) District personnel shall use the approved alternative monitoring method to 

determine compliance with the limits of this rule. 
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431.1-6

(E) Reporting and Recordkeeping Requirements 

(1) All records required by this rule shall be maintained at the facility for at least five 

(5) years, and be made available to District staff upon request. 

(2) Except at electric utility generating facilities and refineries, a person burning 

gaseous fuel, other than exclusively natural gas, in stationary equipment requiring 

a PTO, shall submit to the APCO annual reports of the monthly fuel consumption 

and the total sulfur content of the fuel consumed. The annual report shall be 

submitted no later than 60 days following the end of the reporting year, and shall 

consist of the amount of any gaseous fuel consumed monthly, the applicable 

hourly, daily or monthly average sulfur content as determined by the Continuous 

Monitor or approved alternative monitoring method as specified in subsections 

(D)(1), (D)(2), or (D)(3) of this rule, and total SOx emissions, calculated as SO2. 

(3) A person burning gaseous fuel in stationary equipment located at electric utility 

generating facilities or refineries shall submit to the APCO monthly reports of the 

daily fuel consumption, the monthly weighted average sulfur content (except for 

natural gas), and the maximum four (4)-hour average sulfur content of the fuel 

consumed, as determined by the device specified in subsection (D)(2) of this rule 

and the total SOx emissions, calculated as SO2. The report shall be submitted no 

later than 30 days following the end of the reporting month. 

(4) The person operating a continuous monitor shall keep records as specified in 

clause (D)(2)(b)(i) for monitor breakdown (s) 

(F) Test Methods 

The following may be used by the APCO to verify compliance with the provisions of this 

rule: 

(1) For determination of compliance with sulfur content requirements of section (C): 

(a) The reference method for determining the concentration of sulfur 

compounds in a gaseous fuel, calculated as H2S, shall be South Coast Air 

Quality Management District (SCAQMD) Method 307-91 - Determination 

of Sulfur in a Gaseous Matrix, or any other method demonstrated by the 

applicant to be equivalent and approved in writing by the APCO, the 

CARB, and the Regional Administrator of the EPA, Region IX, or their 

designees, or 
AVAQMD Rule 431.1

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431.1-7

(b) Data obtained from a continuous monitor, which is required to be installed 

and properly operated according to section (D) and as approved by the 

APCO pursuant to the requirements specified in Attachment A. 

(2) The gross heating value of gaseous fuels shall be determined by ASTM Method D 

3588-91 or, if applicable, ASTM Method D 4891-89. 

(3) The methane content of gaseous fuels shall be determined by ASTM Method D 

1945-81. 

(G) Exemptions 

Unless otherwise specified, and provided that the person seeking the exemption supplies 

proof and verification upon request of applicable criteria to the satisfaction of the APCO, 

the provisions of this rule shall not apply to the following: 

(1) A person selling, for use in the jurisdiction of the District, any gaseous fuel not 

complying with subsections (C)(1) and (C)(3) provided that: 

(a) The gaseous fuel is delivered directly to a sulfur removal unit which is in 

full operation and which reduces the sulfur content to the limits specified 

in subsections (C)(1) and (C)(3); 

(b) The seller notifies the APCO prior to any such sale of the quantity, heating 

value, and composition of the gaseous fuel to be sold; and 

(c) The buyer has an approved ATC and/or PTO for the sulfur removal unit 

that will be used to treat the purchased gas. 

(2) Gaseous fuels containing sulfur used in the production of sulfur or sulfur 

compounds. 

(3) Waste gases being burned provided that: 

(a) The gross heating value of such gases is less than 2670 kilocalories per 

cubic meter (300 British Thermal Units per cubic foot) at standard 

conditions; and 

(b) Any supplemental fuel used to burn such waste gases does not contain 

sulfur or sulfur compounds in excess of the amount specified in this rule. 

(4) Gases vented to a control system pursuant to District Rule1173. 

(5) Gases vented intermittently to fuel gas or waste disposal system from pressure 

control valves, sight glasses, compressor bottles, sampling systems, and pump and 

compressor case vents. 
AVAQMD Rule 431.1

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431.1-8

(6) Any facility which emits less than five (5) pounds per day total sulfur compounds, 

calculated as H2S, from the burning of gaseous fuels other than natural gas. 

Emissions of total sulfur compounds shall be measured based on fuel analysis, 

using the test method specified in subsection (F)(1), and the maximum daily 

gaseous fuel consumption. This exemption shall not apply to the requirement of 

subsection (C)(1). 

(7) A person is exempt from the requirements of subsection (D)(1) if the person 

demonstrates to the satisfaction of the APCO that the supplier of the gaseous fuel 

has complied with the requirements of section (D) for such fuel. 

(8) On or after July 1, 1997, a person previously in compliance with the limits 

specified in Table 1 of this rule shall be exempt from the requirements of 

subsection (C)(3) provided that: the alternative monitoring method pursuant to 

section (D) yields no more than three individual readings in a calendar year in 

excess of the limits specified in Table 1; that no single reading exceeds a fuel 

sulfur limit by 25 percent; and that the sampling frequency is no longer than once 

per week. 

See SIP Table at http://www.avaqmd.ca.gov/Modules/ShowDocument.aspx?documentid=921 
AVAQMD Rule 431.1

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431.1-9

ATTACHMENT A 

SECTION I 

REQUIREMENTS FOR CONTINUOUS 

FUEL GAS MONITORING SYSTEM (CFGMS) 

A continuous fuel gas monitor used for determining the sulfur content of any gaseous fuel shall: 

(1) Continuously monitor and record the concentration by volume (dry basis) of sulfur 

compounds in ppmv as H2S in the gaseous fuel. 

(2) Have the span value of the monitor set so that all readings fall between 20 and 95 percent 

of scale. 

(3) Check for calibration drift of the monitoring system at least once daily (approximately 24-

hr interval) at two concentrations, one high level and one low level. Whenever the daily 

high level or low level calibration drift exceeds 5% of analyzer full scale span, the 

monitoring system shall be deemed to be out of control and subject to the requirements of 

subsection (D)(2(b) of this rule. 

(4) Determine the relative accuracy of the monitor which shall be no greater than 20 percent 

of the mean value of the reference method test data. 

(5) Be able to record negative values of zero drift. 

(6) Report the concentration of the sulfur compounds calculated as H2S. 

SECTION II 

REQUIREMENTS FOR CONTINUOUS 

EMISSIONS MONITORING SYSTEMS (CEMS) 

A stack CEMS used for monitoring the sulfur dioxide emissions from the burning of any gaseous 

fuel shall: 

(1) Continuously monitor and record the concentration by volume (dry basis, zero percent 

excess air) of sulfur compounds in ppmv as SO2 emitted into the atmosphere; 

(2) Include either an oxygen monitor for correcting the data for excess air or a fuel gas and 

exhaust gas flowmeter for the determination of mass emissions; 

(3) Have the span value of all the monitors set so that all readings fall between 20 and 95 

percent, for four-hour and daily averages, and between 10 and 95 percent, for monthly 

averages, of full scale; 

(4) When using an oxygen monitor for the correction of excess air, be able to measure a 

sulfur compound concentration emission limit of 5 ppm (dry basis, zero percent excess 

air), which is stoichiometrically equivalent to the limit of sulfur compound content of 40 

ppm calculated as hydrogen sulfide in the gaseous fuels; 

(5) Use District Methods 100.1 or 6.1 (as applicable for sulfur compound analysis) and 

SCAQMD Method 3.1 (for oxygen content analysis), or SCAQMD Method 2.1 (for 

flowrate determination), whichever is applicable, or any other methods demonstrated by 
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431.1-10

the applicant to be equivalent and approved in writing by the APCO and the CARB, and 

the Regional Administrator of the EPA, Region IX, or their designees, for conducting the 

relative accuracy evaluations. The relative accuracy limit shall be 1 ppm and zero drift 

(2-hour and 24-hour) and calibration drift (2-hour and 24-hour) limits for sulfur 

compounds monitor shall be 5 percent of the span range; and 

(6) Check for calibration drift of the monitoring system at least once daily (approximately 24-

hr interval) at two concentrations, one high level and one low level. Whenever the daily 

high level or low level calibration drift exceeds 5% of analyzer full scale span, the 

monitoring system shall be deemed to be out of control and subject to the requirements of 

subsection (D)(2)(b) of this rule. 

(7) Facilities burning fuel gas subject to this rule shall comply with the requirements of Rule 

218 and 218.1(proposed) except where specific requirements have been incorporated into 

this rule. 

SECTION III – 

GUIDELINES FOR APPROVAL OF 

ALTERNATIVE MONITORING PLAN 

BY THE APCO 

In lieu of a continuous fuel gas monitoring system (CFGMS) or a continuous emission 

monitoring system (CEMS), a person subject to this rule may submit an alternative monitoring 

plan to the APCO, the California Air Resources Board (CARB), and the Regional Administrator 

of the Environmental Protection Agency (EPA), Region IX, or their designees. for their review 

and decision. 

(1) A test program to determine the correlation between H2S and total sulfur in the fuel gas 

using SCAQMD Method 307-91. If a correlation is established, a colorimetric test, or 

other alternative method approved by the APCO as being equivalent or better in 

establishing such correlation, may be conducted regularly to determine total sulfur using 

H2S as a surrogate. 

(2) An error analysis between colorimetric, or other approved alternative method readings 

and the total reduced sulfur analysis obtained from SCAQMD Method 307-91. To 

demonstrate equivalency between the two methods of analyses, the relative accuracy shall 

not exceed 20 percent of average SCAQMD Method 307-91 readings. 

(3) A schedule for a daily or more frequent analysis of the fuel gas for H2S using the 

colorimetric test, or other approved alternative method, and a minimum weekly analysis 

of the fuel gas using SCAQMD Method 307-91. A different frequency of analysis may 

be used if the APCO determines that such frequency will ensure compliance with the 

daily total sulfur limits of this rule. 

(4) When the sulfur level is suspected to be at or above the sulfur content requirements of 

Table 1 as determined by the colorimetric or other alternative method, a procedure to 

obtain at minimum a daily sample to be tested according to SCAQMD Method 307-91 

until three consecutive daily samples show that total sulfur is below the sulfur content 

requirements of Table 1.