United States Environmental Protection Agency,

Region IX, Air Division

Technical Support Document

for

EPA's Notice of Proposed Rulemaking

on revisions to the 

Arizona State Implementation Plan 

as submitted by the State of Arizona 

for the Maricopa County Air Quality Department 

EPA's Analysis of

Maricopa County Air Quality Department 

Rule 300 - Visible Emissions

March 2010

Prepared by Joanne Wells

Approved by Andrew Steckel
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Maricopa County Air Quality Department (MCAQD)

Rule 300 - Visible Emissions

1. Rule Adoption and Submittal Chronology

On April 12, 1982 (47 FR 15579), EPA incorporated MCAQD Rule 30, Visible Emissions into 

the Arizona SIP. This rule was amended and renumbered as Rule 300 on July 13, 1988 and 

submitted to EPA on January 4, 1990. However, EPA did not take action on this submittal. Rule 

300 was further amended on August 5, 1994 and February 7, 2001, but these versions were not 

submitted for approval to EPA. 

Rule 300 was amended again on March 12, 2008 and submitted to EPA on July 10, 2008. This 

submittal was determined complete by EPA on March 13, 2009. Though we can act only on the most 

recent version of the submitted rule, we have reviewed previously submitted versions.

2. Nonattainment History of Maricopa County

Upon enactment of the Clean Air Act (CAA) Amendments of 1990, Maricopa County was 

initially designated as a “moderate” nonattainment area for the National Ambient Air Quality

Standard (NAAQS) for PM10. Maricopa County failed to attain the NAAQS by December 31, 

1994 and was reclassified as a serious PM10 nonattainment area on June 10, 1996. The region 

still did not attain the standard by December 31, 2006 and continues to be classified as a serious 

nonattainment area for PM10.

Part of Maricopa County and the Apache Junction Pinal County Area were designated 

nonattainment for the 1997 8-hour ozone standard effective June 15, 2004. The 8-hour area was 

not classified and EPA was going to treat the area as a "subpart 1 Basic" nonattainment area, 

until a court decision in December 2006 vacated our implementing regulations in this regard. 

Although EPA proposed to classify the 8-hour ozone nonattainment area as "marginal" based on 

2001-2003 ozone monitoring data, we have not (as of February 2010) finalized that action. The 

pre-existing 1-hour ozone nonattainment area portion of Maricopa County was redesignated to 

attainment and a maintenance plan was approved effective June 14, 2005.

 

3. Rule Summary & Background 

MCAQD Rule 300 is intended to limit the emissions of air contaminants into the ambient air by

establishing standards for visible emissions and opacity. The revisions adopted March 12, 2008

relate to commitments made in Maricopa’s Five Percent Plan for PM10. Since the area did not 

attain the PM10 NAAQS by December 31, 2006, Arizona had to submit to EPA a Five Percent 

Plan by December 31, 2007. This Plan must demonstrate 5% reductions per year in emissions, 

and MCAQD revised Rule 300 to implement a control measure and increase compliance with 

existing rules for the Five Percent Plan.
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The March 12, 2008 submitted version of Rule 300 would revise the 1982 SIP–approved version 

Rule 30 by: 

 Renumbering the rule to Rule 300, updating the format and adding sections: 101, Purpose; 102,

Applicability; 200, Definitions; 300, Standards; and 500, Monitoring and Records.

 Changing the limit for opacity (Section 301) from 40% to 20% opacity for a period aggregating 

more than three minutes in any 60 minute period.

 Adding the four exceptions in Section 302: 302.1, Charging Electric Arc Furnaces; 302.2,

Emergency Diesel Generators (EDGs) and Equipment; 302.3, Firing of Ordnance at Test 

Facilities; and 302.4, Opacity Training.

 Adding Section 501, Compliance Determination using EPA Method 9 as modified by EPA

Reference Method 203B.

 Making various minor editorial changes such as renumbering, definitions, and several word

additions and title changes to improve clarity. 

 

4. Rule Evaluation

EPA is primarily using the following three criteria to evaluate Rule 300.

a. Rule Stringency – Maricopa County is a serious PM10 nonattainment area, therefore the area is 

subject to CAA §189 PM requirements regarding Reasonably and Best Available Control 

Measures (RACM and BACM).

b. Enforceability – CAA §110(a)(2)(A) requires that regulations submitted to EPA for SIP 

approval must be clear and legally enforceable. 

c. Anti-Backsliding - CAA §110(l) and §193 restrict certain SIP revisions that would relax 

existing SIP-approved requirements. 

EPA must compare the March 12, 2008 version of Rule 300 with the SIP-approved Rule 30. 

The revisions made to Rule 30 and later to Rule 300 strengthen the SIP rule by lowering the 

opacity limit from 40% to 20%. This was further strengthened by changing the procedures for 

determining compliance with the 20% opacity limitation from “averaging to aggregating”. This 

form of data reduction for 20% opacity standard limits the number of excursions over the 20% 

visible emission standard and results in more consistent compliance with the standard.

The four exceptions included in Section 302 of Rule 300 address a small number of very specific 

sources of emissions and each exception includes reasonable limits on excess emissions of 

visible emissions. 

The addition of Section 500, Monitoring and Records, includes appropriate test and data 

reduction methods improving enforceability of the rule.
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Since the MCAQD is classified as a serious nonattainment area for PM10, the rule must meet 

requirements for RACM and BACM. Generally, the 20% opacity limit meets the requirements 

for both RACM and BACM.

The cumulative changes made to Rule 30 / Rule 300 greatly improve the clarity, enforceability, 

and stringency of the rule, and EPA finds that Rule 300 reasonably fulfills the three evaluation 

criteria.

5. Rule Deficiency – No deficiencies were identified in Rule 300.

6. Additional Recommendations for the Next Rule Revision - The following revisions are not 

currently the basis for rule disapproval, but are recommended for the next time the rule is 

amended.

1. Section 200- Definitions: for clarity add a definition of visible emissions. See, for 

example, San Joaquin Valley Unified Air Pollution Control District Rule 4101, Visible 

Emissions, section 3.4. 

2. Section 302.1 – Charging Electric Arc Furnaces: please evaluate the need for this 

exception since it is possible that there are no electric arc furnaces for which construction 

commenced prior to February 2, 1963 currently operating in Maricopa County . 

3. Section 302.2 – Emergency Diesel Generators (EDGs) and Equipment: please evaluate

non-emergency operational testing requirements for these emergency diesel generators 

and equipment and see if there are reasonable time limits, such as minutes per hour and 

hours per month to ensure that excess emissions are limited for this activity. See, for 

example, San Diego Air Pollution Control District Rule 69.4, Stationary Reciprocating 

Internal Combustion Engines, (b) Exemptions (2) (iii): “Any emergency standby engine at 

a nuclear power generating station subject to the requirements of the Nuclear Regulatory

Commission provided that the operation of the engine for non-emergency purposes does 

not exceed 200 hours per calendar year.” 

4. Section 302.3 Firing of Ordnance at Test Facilities - please define “short periods of time” 

and describe a reasonable number of hours per month or year to ensure that excess 

emissions from this activity are appropriately limited by a reasonable time limit.

7. EPA Action – EPA staff recommends full approval of the July 10, 2008 submittal of 

MCAQD Rule 300 – Visible Emissions, amended on March 12, 2008.

8. References

a. MCAQD Rule 300 - Visible Emissions, adopted March 12, 2008.
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b. MCAQD Rule 30 – Visible Emissions, approved into SIP April 12, 1982

c. “Notice of Final Rulemaking, Maricopa County Air Pollution Control Regulations, Rule 300-

Visible Emissions, Date of Adoption: March 12, 2008.”