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Pollution & HealthState Air Regulations Can Go Above and Beyond National Standards 

State Air Regulations Can Go Above and Beyond National Standards 

State Air Regulations Can Go Above and Beyond National Standards 

State and native regulators can and may work to scale back particulate matter, ozone, and NOx emissions even when national standards are met. 

States and native air quality regulators have the legal authority to set particulate matter (PM), ozone, and nitrogen oxides (NOx) emissions standards and adopt regulations for these pollutants after they are already in attainment of the national ambient air quality standards (NAAQS) set by the U.S. Environmental Protection Agency (EPA) under the federal Clean Air Act (CAA). PM, ozone, and NOx are harmful pollutants that cause severe health effects that may range from respiratory ailments to cardiovascular harm and even premature death; these health harms disproportionately impact low-income communities of color. NOx are also a precursor to PM and ozone pollution (and are regulated as such). When an area is in nonattainment of the NAAQS, a state is required to design control measures to come back into attainment. But PM, ozone, and NOx contribute to health and environmental harms even in areas that meet the NAAQS. Regulators in those areas can and may work to attain further pollution reductions through continued regulation.

States have two potential regulatory pathways to accomplish that: First, if a state has not adopted air quality standards which can be more stringent than the federal NAAQS, the CAA allows states to proceed to adopt recent rules as an element of their State Implementation Plan (SIP) to drive continued maintenance of the federal NAAQS. Second, states can adopt recent rules independently of the SIP process. If a state has adopted its own more stringent air quality standards, the CAA grants states the discretion to control to attain those standards (as an element of their SIP or otherwise) even after they meet the NAAQS. States may implement regulations independent of stricter statewide air quality standards to enhance air quality.

Legal Evaluation

Below, I’ll address these two regulatory pathways in turn, primarily specializing in the query of whether state and native air quality regulators can decide to adopt additional pollutant reduction regulations when an area is in attainment of the NAAQS—even when the state doesn’t have its own, more stringent ambient air quality standards.

States’ Duty to Maintain Attainment Status

States that don’t have air quality standards which can be more stringent than the federal NAAQS can proceed to adopt recent rules as an element of a SIP, per CAA authority, to display continued maintenance of the federal NAAQS. Actually, the CAA encourages ongoing regulation of criteria pollutants and their precursors to stop deterioration of air quality and maintain clean air, even in areas already meeting the NAAQS.

The CAA’s emphasis on not only “reduction” but “elimination” of pollutants begins in its preamble, where Congress highlights pollution prevention as a key strategy for air quality management and provides the legal foundation for states’ and native governments’ roles. That theme continues throughout, from the Prevention of Significant Deterioration program, which helps protect attainment areas from pollution brought on by recent sources, to ongoing monitoring requirements for attainment areas. And anytime there’s a recent or revised NAAQS, CAA § 110 requires states to submit pollution control plans, called State Implementation Plans (SIPs), that “provide[] for implementation, maintenance, and enforcement” of the NAAQS (emphasis added). All states must submit SIPs, no matter attainment status. States which have at all times been in attainment are required to enumerate of their SIPs the control measures the states will implement to keep up attainment of the NAAQS.

Section 175A of the CAA also requires areas which can be redesignated from nonattainment to attainment to proceed monitoring emissions; those areas must proceed to control pollutants as a way to stay in attainment. A former nonattainment region with monitoring data showing that it currently attains an air quality standard can submit a “redesignation request” and “maintenance plan” as a revision to its SIP. The upkeep plan outlines how the realm will proceed to satisfy the NAAQS for at the very least 10 years after redesignation to attainment. And eight years after redesignation, states must submit one other SIP revision showing how they are going to maintain the NAAQS for 10 years after the expiration of the initial 10-year period. A maintenance plan consists of a future 12 months emissions inventory, an attainment 12 months emissions inventory, provisions for continued operation of the monitoring network, verification of continued attainment, and a contingency plan. The longer term 12 months emissions inventory includes an accounting of the state’s ongoing regulatory decisions to maintain the realm in maintenance. Because of this states have an ongoing obligation to control (and even add recent regulations) when that’s needed to keep up the NAAQS.

As an element of the contingency plan, states and/or local air regulators must discover measures they are going to absorb the event of a NAAQS violation. But state air regulators don’t must wait until an area falls out of maintenance to adopt recent rules ensuring the NAAQS could be met. In EPA’s final approval of the Detroit, Michigan area’s redesignation request and maintenance plan in May, the agency indicated that states may adopt control measures prior to the actual triggering of a maintenance plan contingency provision. In response to a comment contending that Michigan’s maintenance plan allows the state “an excessive amount of discretion in choosing and implementing contingency provisions,” EPA explained that already-adopted control measures can assist an area achieve a fast turnaround back to attainment when there are issues:

The emissions reductions from these programs…could be achieved more quickly because the State has already passed through the adoption process. To ban a State from using any control measure adopted prior to the actual triggering of a maintenance plan contingency provision would only penalize states which can be proactive in addressing anticipated air quality problems.

Some courts have even interpreted CAA Sections 175A(d), 182(b), and 172(c)(1) to mean that states searching for redesignation for ozone and PM2.5 must provide for the implementation of reasonably available control measures (RACM) and fairly available control technology (RACT) —that are applicable to nonattainment areas—of their SIPs (e.g., the Sixth Circuit Court of Appeals in Wall v. U.S. E.P.A. and Sierra Club v. U.S. E.P.A.).

Washington and Ohio are two examples of states which have adopted recent rules, even for areas which can be already in maintenance or attainment of the NAAQS. Washington has adopted California’s clean automobile standards, despite the fact that most of the state (apart from Whatcom County) is in maintenance for all of the NAAQS. Washington’s adoption of those stricter standards comes on the heels of the termination of its emission testing program in 2020 attributable to the state’s significant improvement in air quality and almost statewide NAAQS attainment. The state’s Department of Ecology has expressed confidence that “air quality goes to improve, even without this program [as] recent cars [become] cleaner,” and because the state “proceed[s] to reduce greenhouse gas emissions from motorcars — the most important source of carbon pollution in Washington.” Washington’s clean automobile rule shows how even where air quality has markedly improved, some states are still continuing to adopt forward-thinking regulations. Moreover, Ohio adopted a rule in 2022 limiting the emissions of NOx from stationary industrial sources. Some areas of the state are in nonattainment for ozone, while others are in maintenance. And while the rule is meant to assist bring the nonattainment areas into attainment, it also applies in maintenance areas.

State Discretion to Pursue Cleaner Air Quality than the NAAQS

The CAA also affords states discretion to pursue air quality that exceeds the federal NAAQS, even when the federal NAAQS have already been met. States can do that by setting standards that transcend the federal NAAQS and implementing regulations designed to realize those standards. They may implement regulations independent of more stringent air quality standards as a way of achieving cleaner air quality. In accordance with CAA § 116, “[n]othing on this chapter shall preclude or deny the appropriate of any State or political subdivision thereof to adopt or implement (1) any standard or limitation respecting emissions of air pollutants or (2) any requirement respecting control or abatement of air pollution[.]” The Supreme Court in Union Electric Company v. E.P.A., 427 U.S. 246, 265 (1976) has also made clear that “[s]tates may submit implementation plans more stringent than federal law requires[.]” Thus, the CAA sets a floor for regulation of air pollution, not a ceiling.

As an example, the California Health and Safety Code provides California air districts with authority to control air pollutants, including the choice to adopt stricter emission limits than those set by each EPA and the California Air Resources Board. California’s SIP includes air district plans to satisfy each the NAAQS and California’s own tougher ambient air quality standards. Over again stringent standards are included in a state’s SIP and approved by EPA, they turn out to be federally enforceable. And states have “the facility to find out which sources [are] burdened by regulation and to what extent[,]” giving them broad discretion to pick out the control measures they’ll include in a SIP. So if a state already has, or chooses to adopt, regulations for PM, ozone, and NOx that transcend the NAAQS, local air regulators are well inside their rights to press for extra pollutant reductions even when the NAAQS have been met.

States may elect to enact standalone regulations that are usually not an element of their SIP. This authority stems not only from the CAA, but additionally from the Tenth Amendment of the U.S. Structure, which reserves to states all powers not expressly delegated to the federal government. These powers include broad authority to guard public health, safety, and welfare, referred to as “the police power,” which encompasses the power to enact standards and rules to scale back air pollution. States’ own constitutions and statutes may further define the scope of their regulatory authority, establish the legal framework for enacting regulations, and delegate authority to specific state agencies to control emissions. Such standalone regulations can be enforceable only by the state and never by the federal government. To ensure that these regulations to be effective, states should be sure that they’re well-grounded in state law and comply (and don’t conflict) with relevant federal laws and constitutional principles to avoid legal challenges and preemption issues.


The CAA is structured not only to attain air quality standards, but additionally to stop air pollution and maintain standards over the long run. Because of this, the Act allows states wide discretion to enact regulations designed to enhance air quality, even in states currently in attainment with the federal NAAQS. Given the substantial health harms from PM, ozone, and NOx even at levels below the NAAQS, state regulators should proceed to proactively regulate these emissions using all the tools available.

air pollution, Clean Air Act, Climate Change, public health


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