Colorado’s Efforts to Attain the Ozone National Ambient Air Quality Standards, 1018 COBJ, Vol. 47, No. 9 Pg. 49

Position::Vol 47, 9 [Page 49]

47 Colo.Law. 49

Colorado’s Efforts to Attain the Ozone National Ambient Air Quality Standards

Vol. 47, No. 9 [Page 49]

Connecticut Bar Journal

October, 2018



This article discusses ozone regulation in Colorado and the state’s efforts to attain compliance with national air quality standards.

Ozone is one of six “criteria” pollutants regulated under the federal Clean Air Act (the Act).[1] Unlike most regulated pollutants, ozone is not emitted directly by a source. Instead, ozone is a gas that is formed when other pollutants called “ozone precursors” react in the atmosphere in the presence of sunlight. Stratospheric ozone in the upper atmosphere protects us from the sun’s harmful rays, but ground-level (i.e., tropospheric) ozone causes harmful health effects.

Colorado’s ozone levels have gradually improved over the years, but additional reductions are needed to keep improving public health and to attain air quality standards. Ozone concentrations in the Denver Metro/North Front Range (DMNFR)2 area can exceed federal standards, particularly during the summer months of June through September. These exceedances put many Coloradans at risk for asthma and other respiratory conditions. Colorado has comprehensive ozone regulations, but the DMNFR area may face significantly more burdensome requirements if it continues to violate ozone standards.

How is Ozone Regulated?

Under the Act, the U.S. Environmental Protection Agency (EPA) promulgates primary and secondary National Ambient Air Quality Standards (NAAQS) for ozone and other criteria pollutants to protect public health and welfare. The primary standards must reflect a level of the pollutant “requisite to protect the public health.”3 EPA must consider only factors related t o health when setting the primary standard, and not economic factors.4 The secondary standard protects the “public welfare” and usually considers factors such as the pollutant’s impact on vegetation and the ecosystem.5 Within two years of promulgating the NAAQS, EPA must designate areas as being in attainment or non attainment of the NAAQS.6 An area attains the ozone NAAQS if air quality monitoring shows ambient ozone concentrations at or below the NAAQS.7 States have flexibility, within federal requirements, to determine how to attain the NAAQS.

Designations and State Implementation Plans

Section 110 of the Clean Air Act requires every state to develop and submit a state implementation plan (SIP) within three years after EPA promulgates or revises a NAAQS for any criteria pollutant, whether or not the state contains a nonattainment area; these SIPs are called “infrastructure SIPs.”8 Infrastructure SIPs contain permitting, enforcement, monitoring, and certain other elements of a regulatory program.9 Infrastructure SIPs also contain “good neighbor” provisions to protect downwind states from the interstate transport of pollution.10

States with areas designated nonattainment face additional requirements set forth in the Act in Title 42 USC, Chapter 85, Subchapter I, Part D, subpart 1 (nonattainment provisions in general) and subpart 2 (additional provisions for ozone nonattainment areas). The ozone requirements of subpart 2 are more specific than, and in some cases explicitly supersede, the general requirements of subpart 1.11

Section 172 of the Act (in subpart 1) requires states to submit a SIP revision within three years after an area is designated as nonattainment.12 Ozone nonattainment areas are classified as Marginal, Moderate, Serious, Severe, or Extreme.13 Section 182 of the Act (in subpart 2) requires additional SIP elements with more stringent and cumbersome requirements for higher ozone classifications.14

Ozone nonattainment areas that do not attain the NAAQS by their attainment deadline are reclassified or “bumped up” and required to submit a more stringent SIP revision.15 Conversely, if a nonattainment area comes into attainment, the state may request redesignation as an attainment area and submit maintenance SIPs covering the next two 10-year periods.16

Ozone NAAQS and Colorado’s Status

EPA promulgated the first ozone NAAQS in 1979 and promulgated revisions in 1997, 2008, and 2015. Colorado’s status with respect to each NAAQS revision is discussed below.

1997 NAAQS (revoked). In 1997, the EPA adopted an eight-hour ozone standard of 0.08 parts per million (ppm), referred to as the 1997 NAAQS.17 Implementation of the 1997 NAAQS was delayed by litigation and Congressional action.18 EPA was sued for failing to make timely designations and entered a consent decree requiring it to designate areas by April 15, 2004.19 In 2002, Colorado and 11 other states entered Early Action Compacts (EAC) with EPA to defer the designation of 14 nonattainment areas, subject to the submittal of SIP revisions requiring early action to reduce ozone and certain other requirements.20 EPA extended Colorado’s attainment deadline several times pursuant to the EAC program until the Denver area was designated nonattainment effective November 20, 2007, based on air quality data showing a violation of the standard.21 In July 2009, Colorado submitted an attainment demonstration SIP to EPA for the 1997 NAAQS. EPA partially approved it in 2011.[22] Colorado’s ozone design value has not violated the 1997 NAAQS since 2009. EPA revoked the 1997 NAAQS in 2015.23 Colorado never sought redesignation as an attainment area.

2008 NAAQS. EPA lowered the ozone NAAQS to 0.075 ppm24 in 2008.25 The DMNFR was designated a Marginal nonattainment area under the 2008 NAAQS, effective July 20, 2012.26 The region failed to meet its July 20, 2015 attainment deadline[27] and was reclassified as a Moderate nonattainment area.[28] Following the reclassification, Colorado adopted and submitted to EPA a SIP revision with additional ozone control measures and a demonstration (using photochemical modeling) that the DMNFR would attain the 2008 NAAQS in 2017. On July 3, 2018, EPA published a final rule approving the majority of Colorado’s SIP revision, including the attainment demonstration.29 However, unverified 2018 monitoring data show that the DMNFR has very likely failed to attain the standard by the attainment date and may be reclassified as a Serious nonattainment area, resulting in significant new requirements.

2015 NAAQS. EPA further lowered the ozone NAAQS to 0.070 ppm (equivalent to 70 ppb) in 2015. EPA designated many areas as attainment/ unclassifiable in November 2017.[30] On March 9, 2018, EPA defined the thresholds for classifying 2015 NAAQS nonattainment areas.31 On June 4, 2018, EPA published a final rule designating t he DMNFR as a Marginal nonattainment area, and the rest of the state as attainment/ unclassifiable.32 Colorado’s existing SIP likely fulfills many of the Marginal area requirements, although a new baseline emissions inventory will be needed and the adequacy of other SIP elements must be reviewed.33 If the DMNFR misses its August 3, 2021 attainment date it will face reclassification as a Moderate area, triggering additional requirements.

Colorado’s Ongoing Compliance Efforts

Colorado revised its SIP in November 2016 after being reclassified as a Moderate ozone nonattainment area under the 2008 NAAQS.34 The main elements of the SIP revision include:

■ an attainment demonstration,

■ reasonable further progress reductions in volatile organic compounds (VOCs) and oxides of nitrogen (NOx) emissions,

■ reasonably available control technology (RACT) and reasonably available control measures (RACM) requirements,

■ contingency measures in the event of failure to meet a milestone or to attain the standard,

■ a vehicle inspection and maintenance program, and

■ NOx and VOC emission offset ratios for major source permits.35

The SIP and regulations adopted by Colorado in November 2016 addressed the statutory elements, and partially addressed the requirement that Moderate nonattainment area SIPS include provisions requiring RACT for existing facilities that are major sources of VOC or NOx.36 In July 2018, Colorado adopted RACT standards for additional existing combustion sources in the DMNFR, such as engines, boilers, and turbines.37 The state is also currently developing major source RACT standards for certain additional categories of existing major sources, with Air Quality Control Commission (AQCC) hearings anticipated in November 2018.

Colorado further revised its RACT SIP in November 2017 to add certain oil and gas requirements, such as more frequent leak inspections.38 Colorado submitted the SIP revision but EPA has not yet acted on it. The 2017 SIP revision became mandatory39 after EPA published its Control Techniques Guidelines for...

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