431.1 -1

(Adopted November 4, 1977)(Amended September 1, 1978)

(Amended February 2, 1979)(Amended January 8, 1982)

(Amended May 6, 1983)(Amended May 4, 1990)

(Amended April 5, 1991)(Amended September 11, 1992)

(Amended October 2, 1992)(Amended November 17, 1995)

(Amended June 12, 1998)

RULE 431.1. SULFUR CONTENT OF GASEOUS FUELS

(a) Purpose

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

burning of gaseous fuels in stationary equipment requiring a permit to operate by

the South Coast Air Quality Management District (District).

(b) Definitions

(1) BURN means to combust any gaseous fuel, whether for useful heat or by

incineration without heat recovery, except for flaring of emergency vent

gases.

(2) CONTINUOUS EMISSION MONITORING SYSTEM (CEMS) means a

system of equipment that continuously measures and records all parameters 

necessary to directly determine concentrations or mass emissions of

selected pollutants, and which meets all of the requirements of Attachment 

A, Section II.

(3) CONTINUOUS FUEL GAS MONITORING SYSTEM (CFGMS) means

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.

(4) CONTINUOUS MONITOR means a CEMS or CFGMS.

(5) DAILY AVERAGE means 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.

(6) EMERGENCY VENT GAS means any gas released from a process unit as 

a result of any process upset or breakdown.

(7) GASEOUS FUEL means 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.
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(8) LANDFILL GAS means any gas derived through any biological process

from the decomposition of organic waste buried within a waste disposal

site.

(9) MONTHLY WEIGHTED AVERAGE SULFUR CONTENT means 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.

(10) NATURAL GAS means 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.

(11) RECLAIM SOx FACILITY means a facility that has been included in the

RECLAIM (Regional Clean Air Incentives Market) program in accordance 

with the requirements of Rule 2001 "Applicability," and/or which has been 

issued a RECLAIM Facility Permit and is subject to the requirements of

Rule 2011, "Requirements for Monitoring, Reporting, and Recordkeeping

for Oxides of Sulfur (SOx) Emissions."

(12) REFINERY GAS means 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.

(13) SEWAGE DIGESTER GAS means any gas derived from anaerobic

decomposition of organic sewage within its containment.

(14) SMALL REFINER means any person owning or operating a facility in

California that produces materials from the processing of crude oil

provided such facility:

(A) has and at all times had since January 1, 1978, a crude oil capacity

of not more than 55,000 barrels per stream day; and

(B) has not been, at any time since September 1, 1988, owned or

controlled by any refiner that at the same time owned or controlled 

refineries in California with a total combined crude oil capacity of

more than 55,000 barrels per stream day; and

(C) has not been at any time since September 1, 1988, owned or

controlled by any refiner that at the same time owned or controlled 
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431.1 -3

refineries in the United States with a total combined crude oil

capacity of more than 137,500 barrels per stream day; and

(D) has received a two-year extension for compliance with California

Air Resources Board's Phase II Reformulated Gasoline

Requirements.

(15) STANDARD CONDITIONS means the atmospheric state where the 

temperature is 60oF and barometric pressure is 14.7 pounds per square

inch absolute.

(16) STREAM DAY means any day or part of a day when a facility or a process 

unit is in operation.

(c) Sulfur Content Requirements

(1) Natural gas

A person shall not transfer, 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

On or after the applicable compliance dates specified in Table 1, a person

shall not burn in equipment requiring a Permit to Operate, purchase,

transfer, sell or offer for sale for use in the jurisdiction of the District, any

gaseous fuel containing sulfur compounds calculated as H2S, 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 

Period

Compliance Date

On or After

Refinery Gas

Small Refiners

Other Refiners

40

40

4 hrs

4 hrs

May 4, 1996

May 4, 1994

Landfill Gas 150 Daily June 12, 1998

Sewage Digester Gas 40

or

40 and

500

Daily

or

Monthly and

15-minutes

November 17, 1995

November 17, 1995

Other Gases 40 4 hrs May 4, 1994
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431.1 -4

(3) Optional Facility Compliance Plan ("OFCP")

A person may comply with paragraph (c)(2) by achieving equivalent sulfur 

oxides (SOx) emission reductions within the facility, provided that the

applicant submits and complies with an Optional Facility Compliance Plan

("OFCP") which has been approved in writing by the Executive Officer. 

The OFCP shall:

(A) Contain, at a minimum, all data, records, and other information

necessary to determine eligibility for alternative emission control,

including but not limited to:

(i) A list of equipment and a description of the equipment

where the gaseous fuel is being produced and/or burned;

(ii) The amount of fuel produced by and/or to be burned in each 

piece of equipment listed in clause (c)(3)(A)(i);

(iii) The estimated emissions of sulfur dioxide from each piece

of equipment; and

(iv) Historical and projected information on fuel usage;

(B) Demonstrate that daily total SOx emissions under the OFCP from

all sources within the facility regulated under Rule 431.1 would be

less than or equal to SOx emissions that would have been emitted

based on actual total SOx emissions from each source, or the sulfur 

content limits of this rule, whichever results in lower SOx emissions. 

The total SOx emissions generated from the subject fuel shall be

determined using a continuous emission monitoring system

(CEMS) specified in subdivision (d). The total emissions may be

determined by monitoring the sulfur dioxide emissions from at least 

70 percent of the total fuel gas consumed as obtained from a

totalizing meter, and calculating the total emissions using the

CEMS data;

(C) Demonstrate that the permit units subject to the specified rule

emission limitations are in compliance with all applicable District

rules or are on an approved schedule of compliance; and

(D) Demonstrate compliance with the continuous monitoring

requirements as specified in subdivision (d) of this rule.

(4) 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
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431.1 -5

exempt from this rule pursuant to paragraph (g)(8); 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 Executive Officer 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 Executive Officer an application for a fuel gas control 

system within six months of the time of exceedance of the

exemption criteria specified in paragraph (g)(8), or non-compliance 

with the limit;

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

than eighteen (18) months after the time of exceedance; and

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

(d) Monitoring Requirements

(1) Except as provided in paragraph (d)(3), a person burning gaseous fuels,

other than exclusively natural gas, in stationary equipment requiring a

Permit to Operate 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 paragraph (c)(4) of this rule shall comply with

paragraphs (d)(1) and (d)(2) no later than twelve months after the

date a Permit to Construct is issued by the District for a sulfur

removal system or comply with paragraph (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 U.S. EPA 40 CFR, 

Part 60, Appendix F, Procedure 1 for CEMS and, as applicable, for

CFGMS.
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431.1 -6

(A) The quality assurance procedure specified above shall be submitted 

to the District for written approval by the Executive Officer 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 Executive Officer shall be corrected within 72

hours.

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

Executive Officer 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 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 clause

(d)(2)(B)(i) and paragraph (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 

paragraph (c)(4) of this rule may use an alternative monitoring method, in

lieu of the requirements in paragraphs (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 Executive Officers of the District, 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 (c)(4) of this rule shall submit an alternative

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

a Permit to Construct a sulfur removal system is issued.

(C) All monitoring must comply with the approved alternative

monitoring method.
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431.1 -7

(D) District personnel shall use the approved alternative monitoring

method to determine compliance with the limits of this rule.

(e) Reporting and Recordkeeping Requirements

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

least two 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 District Permit to Operate, shall submit to the

Executive Officer 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 paragraphs (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 Executive Officer 

monthly reports of the daily fuel consumption, the monthly weighted

average sulfur content (except for natural gas), and the maximum 4-hour 

average sulfur content of the fuel consumed, as determined by the device

specified in paragraph (d)(1) 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 shall be used by the Executive Officer to verify compliance with the 

provisions of this rule:

(1) For determination of compliance with sulfur content requirements of

subdivision (c):

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

compounds in a gaseous fuel, calculated as H2S, shall be District

Method 307-91 - Determination of Sulfur in a Gaseous Matrix, or 
Rule 431.1 (Cont.) (Amended June 12, 1998)

431.1 -8

any other method demonstrated by the applicant to be equivalent

and approved in writing by the Executive Officers of the District,

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

or their designees, or

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

installed and properly operated according to subdivision (d) and as

approved by the Executive Officer pursuant to the guidelines

specified in Attachment A, or

(C) The results obtained using the approved alternative monitoring

method as specified in (d)(3).

(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 Executive Officer, 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 paragraphs (c)(1) and (c)(2) 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 paragraphs (c)(1) and (c)(2); and

(B) The seller notifies the Executive Officer 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 Permit to Construct and/or Operate 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
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431.1 -9

(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 being burned from fluidized catalytic cracking unit (FCCU)

regenerators subject to District Rule 1105 or Regulation XX.

(5) Gases vented during refinery turnaround pursuant to District Rule 1123 or 

Regulation XX.

(6) Gases vented to a control system pursuant to District Rule 466 and 1173

or Regulation XX.

(7) 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.

(8) Any facility which emits less than 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 paragraph (g)(1), and the

maximum daily gaseous fuel consumption. This exemption shall not apply

to the requirement of paragraph (c)(1).

(9) A person is exempt from the requirements of paragraphs (d)(1) and (d)(2) 

if the person demonstrates to the satisfaction of the Executive Officer that 

the supplier of the gaseous fuel has complied with the requirements of

subdivision (d) for such fuel.

(10) Until December 31, 1998, a person burning LFG is exempt from the

requirements of paragraph (d)(1) and (d)(2) provided that they determine

and report the sulfur content of the fuel gas according to the approved

Rule 1150.1 Compliance Plan for the landfill providing the LFG. If the

person burning LFG elects to use an alternative monitoring method as

specified in paragraph (d)(3), the plan or revision to the plan shall be

submitted to the District by September 1, 1998 and the sulfur content of

the fuel gas shall be determined and reported according to the approved

Rule 1150.1 Compliance Plan for the landfill providing the LFG, until plan 

approval or disapproval.

(11) 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

paragraph (c)(4) provided that: the alternative monitoring method

pursuant to paragraph (d)(3) yields no more than three individual readings
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431.1 -10

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.
Rule 431.1 (Cont.) (Amended June 12, 1998)

431.1 -11

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 subparagraph (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.
Rule 431.1 (Cont.) (Amended June 12, 1998)

431.1 -12

ATTACHMENT A

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 H2S in the gaseous fuels; 

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

and District Method 3.1 (for oxygen content analysis), or District Method 2.1 (for 

flowrate determination), whichever is applicable, or any other methods

demonstrated by the applicant to be equivalent and approved in writing by the

Executive Officers of the District 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 subparagraph (d)(2)(B) of this rule.

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

Rule 218 except where specific requirements have been incorporated into this rule.
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431.1 -13

ATTACHMENT A

SECTION III

GUIDELINES FOR APPROVAL OF

ALTERNATIVE MONITORING PLAN

BY THE EXECUTIVE OFFICER

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 Executive Officers of the District, 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 District Method 307-91. If a correlation is established, a

colorimetric test, or other alternative method approved by the Executive Officer 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 District Method 307-

91. To demonstrate equivalency between the two methods of analyses, the relative 

accuracy shall not exceed 20 percent of average District 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 District Method 307-91. A different frequency of

analysis may be used if the Executive Officer 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 

District Method 307-91 until three consecutive daily samples show that total sulfur 

is below the sulfur content requirements of Table 1.