(Adopted January 9, 1976)(Amended April 1, 1977)(Amended August 5, 1977)

(Amended April 6, 1979)(Amended August 7, 1981)

RULE 218. STACK MONITORING

(a) Stack Monitoring Requirements

(1) The owner or operator of any equipment described below shall provide; properly install, 

maintain in calibration, in good working order and in operation; approved stack monitoring 

systems to measure the concentration of the following air contaminants and diluent gases in the 

emissions from the sources indicated. The owner or operator shall also provide any other data 

necessary for calculating air contaminant emission rates.

(A) Oxides of nitrogen (NOx), and carbon dioxide (CO2) or oxygen (02), from steam generators 

with a heat input of 63 million kilogram calories (250 million British Thermal Units) or more per 

hour and with a use factor of at least 30 percent.

(B) Sulfur dioxide (SO2) from steam generators with a heat input of 63 million kilogram calories 

(250 million British Thermal Units) or more per hour and with a use factor of at least 30 percent 

if control equipment is used.

(C) Oxides of nitrogen (NOx) from all nitric acid production plants.

(D) Gaseous sulfur compounds calculated as sulfur dioxide (SO2) from all sulfuric acid 

production plants, carbon monoxide boilers or furnaces of the regenerators of fluid catalytic 

cracking units, and all fluid cokers.

(E) Sulfur dioxide (SO2) from sulfur recovery plants with oxidizing tail gas units, and with 

reducing tail gas units using continuous incineration for control of hydrogen sulfide (H2S).

(2) The Executive Officer may require a person to provide, properly install, maintain in 

calibration, in good working order and in operation, an approved stack monitoring system to 

measure air contaminants in emission gases when that person installs, operates, or uses any 

equipment which emits 900,000 kilograms (992 tons) or more per year of carbon monoxide (CO) 

or 90,000 kilograms (99 tons) or more per year of any air contaminant except carbon monoxide 
(CO). The Executive Officer shall report to the District Board in writing when he requires the 

installation of a stack monitoring system under the provisions of this subpart.

(b) Approval of Monitoring Systems

(1) All monitoring systems to be installed after April 6, 1979, require an initial approval by the 

Executive Officer, prior to installation. The Executive Officer shall act upon an application for 

initial approval within 30 days after filing or within 30 days after the applicant furnishes further 

information, plans and specifications requested to complete an application. Upon completion of 

installation, a person operating or using a stack monitoring system shall undertake a series of 

tests to demonstrate the acceptability of the system's performance pursuant to (c) below. Within 

6 months of initial operation, data from such tests shall be submitted to the Executive Officer for 

approval. If satisfactory performance is demonstrated, a final approval of the system shall be 

granted.

(2) A person operating a monitoring system installed on or before April 6, 1979, shall, by June 1, 

1979, submit a plan to the Executive Officer outlining steps to achieve compliance with the 

performance specifications of (c) below as expeditiously as practicable, but in no event later than 

March 2, 1981.

Each plan shall include, but shall not necessarily be limited to, dates and methods for achieving 

the following increments of progress:

1.Submit test results.

2.Negotiate and sign contracts.

3. Commence modification or replacement of non-complying systems.

4. Complete modification or replacement of non-complying systems.

5. Submit final test results.

6. Achieve final compliance with (c) below on or before

March 2, 1981.

Non-complying systems shall be operated at the level of performance indicated by test results. 

Each system shall be operated in accordance with the plan.

(3) A person operating an approved monitoring system shall affix such written notice of approval 

or a legible facsimile upon the equipment in a manner such that it is clearly visible and legible. 

In the event that the equipment is so constructed or operated that the notice of approval or its 
legible facsimile cannot be so placed, such notice or legible facsimile shall be mounted on a 

location approved by the Executive Officer.

(c) Monitoring System Standards

(1) The monitoring system shall be installed at a location such that air contaminant and diluent 

gas concentration measurements can be made which are representative of the stack emissions of 

the affected facility.

(2) Prior to final approval of the monitoring system, it shall meet, and it shall thereafter be 

operated in accordance with, the following performance and equipment specifications:

(A) Monitors for Gaseous Air Contaminants

Parameter Specifications

(i) Operational Period* Greater than or equal to 168 hours. 

(ii) Calibration Error** Less than or equal to 5 percent. 

(iii) Response Time Less than or equal to 10 minutes. 

(iv) Zero Drift (2-hour)** Less than or equal to 2 percent of full scale reading. 

(v) Zero Drift**(24-hour) Less than or equal to 2 percent of full scale reading.

(vi) Calibration Drift (2-hour)** Less than or equal to 2 percent of scale reading.

(vii) Calibration Drift (24-hour)** Less than or equal to 2.5 percent of full scale reading.

(viii) Relative Accuracy** Less than or equal to 20 percent of the mean value of the reference 

method test data or less than or equal to 10 percent of the allowed concentration, whichever is 

greater.

(B) Monitors for Diluent Gases

Parameters Specifications

(i) Operational Period* Greater than or equal to 168 hours.

(ii) Calibration Error** Less than or equal to 5 percent.

(iii) Response Time Less than or equal to 10 minutes.

(iv) Zero Drift (2-hour)** Less than or equal to 0.4 percent CO2 or 02.
(v) Zero Drift (24-hour)** Less than or equal to 0.5 percent CO2 or 02.

(vi) Calibration Drift (2-hour)** Less than or equal to 0.4 percent CO2 or 02.

(vii) Calibration Drift (24-hour)** Less than or equal to 0.5 percent CO2 or 02.

(3) The monitoring system shall be operated according to the following standards:

(A) Calibration gases shall meet the following criteria:

(i) For gaseous air contaminant monitors, the mixture shall be certified to be within 2 percent of 

the stated value.

(ii) For carbon dioxide and oxygen monitors, the mixture shall be certified to be within 0.2 

percent carbon dioxide or oxygen of the stated value. Ambient air may be used for oxygen 

monitors if the span is higher than 21 percent oxygen.

(B) Zero gases used shall meet the following criteria:

(i) For gaseous air contaminant monitors, the gas shall be certified by the manufacturer to 

contain less than 1 part per million of the air contaminant (except carbon monoxide, less than 10 

parts per million), or alternately, ambient air may be used.

(ii) For carbon dioxide and oxygen monitors, the gas shall be certified by the manufacturer to 

contain less than 100 parts per million of carbon dioxide or oxygen.

(C) Every six months, calibration gases shall be reanalyzed by the National Bureau of Standards 

procedures.

(D) Calibration checks shall be performed at least once each day at regular intervals.

(E) The instrument full scale reading shall be equivalent to approximately 200 percent of the 

concentration limit specified in the applicable rule, or at a value approved by the Executive 

Officer. Oxygen and carbon dioxide instruments full scale readings shall be such that the full 

range of concentrations encountered can be measured.

(F) Regular scheduled maintenance of the monitoring system shall be deferred until the report 

required under Section (e)(2) is made, if the system is measuring a concentration equal to or 

exceeding the emission standard, and if such deferral will not reasonably be expected to result in 

damage to the system.

(G) The monitoring system shall complete a minimum of one cycle of operation (sampling, 

analyzing, and data recording), for each successive 15-minute period.

(H) The requirements of section (c)(3)(G) shall not apply to the following conditions:
(i) Regular calibration checks of the system.

(ii) Routine maintenance and repair of 60 minutes or less duration.

(4) Following final approval, if significant modifications are made to the system, a 

demonstration of the ability of the system to operate in accordance with the specifications of 

(c)(2) may be required at the discretion of the Executive Officer.

(5) Span cell calibration techniques may be employed with in situ monitors, not extracting the 

gas sample from the stack if the criteria of (c)(2)(A)(ii), (vi) and (vii) can be met and if the use of 

the cell provides a check of all analyzer internal mirrors and lenses and all electronic circuitry 

including the source and detector assembly which are normally used in sampling and analysis.

(6) Zero calibration reflector techniques may be employed with in situ monitors, not extracting 

the gas sample from the stack, if the criteria of (c)(2)(A)(iv) and (v) can be met.

(d) Retention of Records

(1) The records of the data obtained from the recording devices of the stack monitoring system 

shall clearly indicate concentrations as specified by the Executive Officer. Records shall be 

maintained by the owner or operator of a monitoring system for a period of at least two years and 

shall be made available to the Executive Officer upon request.

(2) All records of the occurrence and duration of any start up, shutdown or malfunction, 

performance test, evaluation, calibration, adjustment and maintenance of the monitoring system 

as well as calibration gas traceability or span cell specifications documents, shall be retained by 

the monitoring system operator for a period of at least two years and shall be made available to 

the Executive Officer upon request.

(e) Reporting

(1) A person operating a stack monitoring system shall provide a summary of the concentration 

and emission data obtained from such system, as well as any additional information specified by 

the Executive Officer to evaluate the accuracy and precision of the measurements. The summary 

shall be submitted monthly to the Executive Officer within 30 days of the end of the month being 

reported, in the form and manner prescribed by him. The summary shall be available for public 

inspection at the office of the Air Quality Management District.

(2) A person operating a monitoring system shall report any concentration level in excess of the 

regulated limit to the Executive Officer within 96 hours after such occurrence in the form and 

manner prescribed by him. The report shall include the following information:
(A) Time intervals, date, and magnitude of the excess concentration level; nature and cause of 

the excess (if known), corrective actions taken and preventive measure adopted.

(B) Averaging period used for data reporting shall correspond to the averaging period specified 

in the rule governing the concentration limit in question.

(3) Reports of Monitoring System Failure or Shutdown

(A) A person operating a monitoring system shall notify the Executive Officer within 96 hours, 

in a form and manner prescribed by him, in the event of a system failure or shutdown for repair, 

which exceeds 60 consecutive minutes. Zero and calibration checks and routine maintenance do 

not require reporting.

(B) In the case of a monitoring system failure or shutdown for repair, compliance with the 

provisions of subsection (a) is waived for a period not to exceed 96 consecutive hours. Such 

waiver is extended beyond 96 consecutive hours only if a petition for an interim variance is filed 

in accordance with Regulation V and shall terminate at the time the Hearing Board acts upon 

such variance petition.

(f) Exemption

Any source subject to the provisions of (a)(1) above may obtain an exemption from the 

provisions of (a)(1) above upon demonstration to the satisfaction of the Executive Officer that 

the source is not subject to a District rule or regulation prohibiting or limiting the discharge of 

any air contaminants which are the subject of (a)(1).

(g) Definitions

(1) CALIBRATION is an operating condition of the monitoring system whereby the system is 

accurately recording the concentration of the specific air contaminant or diluent gas as evidenced 

by calibration checks, achieved by periodic manual or automatic adjustment.

(2) CALIBRATION CHECK is a procedure to determine the response of the system to a given 

gaseous compound concentration by means of injecting a certified calibration gas mixture into 

the system, or the insertion of a span cell into the internal light path of the analyzer.

(3) CALIBRATION DRIFT** is the change in the monitoring system output over a stated time 

period of normal continuous operation when the air contaminant or diluent gas concentration at 

the time of the measurements is the same known upscale value, or simulated to be the same 

upscale value by use of a span cell.

(4) CALIBRATION ERROR** is the difference between the air contaminant or diluent gas 

concentration indicated by the monitoring system and the known concentration of the span gas or 

the equivalent rating of the span cell.
(5) CALIBRATION GAS is a mixture of the air contaminant gas, or carbon dioxide or oxygen in 

a diluent gas, which, when periodically introduced into the monitoring system, is used to check 

that system's accuracy.

(6) CERTIFIED GAS MIXTURE is a mixture analyzed, by replicate samples, by the 

manufacturer by referring to National Bureau of Standards Reference Materials, such that a 

statement of the precision of the analysis can be made.

(7) DILUENT GAS is a gas present in a calibration gas mixture or in the emissions from a 

source which is present in quantities significantly larger than the air contaminant.

(8) NINETY-FIVE PERCENT CONFIDENCE INTERVAL is the statistically determined range 

within which there is a 95 percent probability all values determined will lie.

(9) OPERATIONAL PERIOD is a minimum period of time during which the monitoring system 

shall operate, according to the performance and equipment specifications, without unscheduled 

maintenance, repair, or adjustment.

(10) PARTS PER MILLION is a volume concentration measurement, indicating the volumetric 

quantity of the gas in question, dispersed in one million volumes of gas mixture, reported on a 

dry basis.

(11) REFERENCE METHOD is the official test method employed by the District to determine 

compliance with the rules.

(12) RELATIVE ACCURACY is the degree of correctness with which the monitoring system 

yields the value of gas concentration of a sample relative to the value given by the reference 

method or to the allowed concentration. This accuracy is expressed in terms of error, which is the 

absolute value of the mean of the differences between the pared concentration measurements 

plus the absolute value of the 95 percent confidence interval. It is expressed as a percentage of 

the mean reference method value or of the allowed concentration. When a rule requires a 

correction of the air contaminant concentration to a specific O2 or CO2 concentration, the 

relative accuracy requirement shall apply to the corrected concentration value.

(13) RESPONSE TIME is the time interval from a step change in the air contaminant or gas 

diluent concentration at the input to the monitoring system to the time at which 95 percent of the 

corresponding final value is reached as displayed on the monitoring system data recorder.

(14) ROUTINE MAINTENANCE is an operation, recommended by the manufacturer, to be 

performed at specified intervals, to preclude system failure. Repairs to a malfunctioning system 

are excluded from this definition.

(15) SPAN CELL is a sealed cell of fixed length, containing a known concentration of an air

contaminant, which is inserted into the internal light path of the analyzer to provide a 

measurement output that corresponds to a known concentration of that air contaminant.
(16) STACK MONITORING SYSTEM, or MONITORING SYSTEM, is the total equipment 

required for the determination of concentrations of air contaminants and diluent gases in a source 

effluent. The system consists of three major subsystems:

(A) Sampling Interface - that portion of the monitoring system that performs one or more of the 

following operations: delineation, acquisition, transportation, and conditioning of a sample of the 

source effluent or protection of the analyzer from the hostile aspects of the sample or source 

environment.

(B) Analyzer

(i) Air Contaminant Analyzer - that portion of the monitoring system that senses the air 

contaminant and generates a signal output that is a function of the concentration of that gas.

(ii) Diluent Analyzer - that portion of the monitoring system that senses the concentration of 

oxygen or carbon dioxide and generates a signal output that is a function of the concentration of 

that gas. This subsystem is required only for sources noted in a (a)(1)(A).

(C) Data Recorder - that portion of the monitoring system that provides a permanent record of 

the output signal in terms of concentration units, including additional equipment such as 

computers required to convert the original recorded value to any value required for reporting.

(17) SYSTEM FAILURE occurs anytime the monitoring system is suspected or known to be 

unable to meet the requirements of (c)(2) or (b)(2), as applicable.

(18) USE FACTOR is the amount of time used per year divided by the amount of time available 

for use per year, expressed as a percent.

(19) ZERO CALIBRATION REFLECTOR is a device which is inserted into the internal light 

path of the analyzer to provide a measurement output that simulates a zero gas concentration.

20) ZERO DRIFT** is the change in the monitoring system over a stated period of time of 

normal continuous operation when the air contaminant or diluent gas concentration at the time of 

the measurements is zero, or is simulated to be zero by use of a zero calibration reflector.

(21) ZERO GAS is a gas containing less than a specified amount of the air contaminant or 

diluent gas which, when periodically injected into the monitoring system, is used to check that 

system's response to the absence of the air contaminant or diluent gas.

*The operational period test performed prior to final approval shall be preceded by a 168 hour 

(minimum) conditioning period during which the system shall be operated without unscheduled 

maintenance, repair, or adjustment.

**Expressed as the sum of the mean value plus the 95 percent confidence interval of a series of 

tests.