The Definitive Guide to Air Emissions Regulations

If you want to learn about environmental compliance and the EPA regulations for air emissions at your facility, you’ve come to the right place.



Over the years, ESC Spectrum has published tons of educational materials on our Source Blog and YouTube Channel, helping thousands of people in the CEMS industry have a better understanding of what regulations their facility falls under and helping them comply.



We’ve created this guide just for you. Whether you’re new to the CEMS world or already know the basics of air emissions regulations, this page is your gateway to environmental compliance mastery.

Table of Contents

The Clean Air Act: A Landmark Passage

On December 31, Congress authorized the Clean Air Act; a landmark passage for the Clean Air Act Amendments including National Ambient Air Quality Standards (NAAQS), Required State Implementation Plans (SIPs), Regulated Hazardous Air Pollutants (HAPs), New Source Performance Standards (NSPS). The enactment of the Clean Air Act of 1970 resulted in a major shift in the federal government’s role in air pollution control. This legislation authorized the development of comprehensive federal and state regulations to limit emissions from both stationary (industrial) sources and mobile sources.


The Clean Air Act focused on reducing outdoor, or ambient, concentrations of air pollutants that cause smog, haze, acid rain, and other problems; reducing emissions of toxic air pollutants that are known, or are suspected of, causing cancer or other serious health effects; and phasing out production and use of chemicals that destroy stratospheric ozone. These pollutants come from stationary sources such as chemical plants and power plants.

timeline of air emissions regulations within the EPA from 1955 - 1990

Air Emissions Regulation Timeline

Let's Review the EPA's History

There have been historical references to bans on burning coal dating back to the 1300s. It wasn’t until between the 1930s – 1970s that US communities started to issue ordinances and take steps to reduce smog. In 1955, the Federal Air Pollution Control Act was put in place, and then followed in 1963, the Federal Clean Air Act was implemented with a focus on cars. In 1967, the Federal Air Quality Act was passed for stationary sources, and then finally in 1970 on December 2nd, the Environmental Protection Agency was created.


On April 30, 1971, the final publication of national air quality standards for 6 common pollutants was announced. National Ambient Air Quality Standards (NAAQS) define the maximum amount of a pollutant averaged over a specified period that can be present in outdoor air without harming public health. The Clean Air Act Amendments of 1970 instruct the EPA to set primary and secondary National Ambient Air Quality Standards. These pollutants are particulate matter, ozone, nitrogen oxides, sulfur oxides, carbon monoxide, and lead.


In 1977, the Clean Air Act Amendments established two new programs: Prevention of Significant Deterioration (PSD) and New Source Review (NSR). The New Source Review (NSR) addressed older facilities that had been “grandfathered” by the original law. This requires older industrial facilities that want to expand to undergo an EPA assessment and install pollution control technologies if the planned expansion would emit more pollutants. PSD applies to new major sources or major modifications at existing sources for pollutants where the area is located is in attainment or unclassifiable with the NAAQS. This requires the installation of BACT, an air quality analysis, an additional impact analysis, and public involvement.


The 1990 Clean Air Act enables plants to be issued allowances based on fixed emission rates, and they will pay stiff monetary penalties for releasing more pollutants than are covered by their allowances. All power plants covered by the Acid Rain Program must install a Continuous Emission Monitoring System (CEMS) and instruments that keep track of how much SO2 and NOx the plant’s individual units are releasing. Power plants keep track of this information hourly and report it electronically to the EPA four times a year. A Power Plant’s program for meeting its SO2 and NOx limits will appear on the plant’s permits, which are filed with the state and EPA.


Reducing both SO2 and NOx had a phased-in approach encompassing two phases for each pollutant.


In 1995, The Acid Rain Program (ARP) began and requires major emission reductions of SO2 and NOx from electric utilities. Sulfur Dioxide and nitrogen oxides are the principal pollutants that cause acid precipitation. SO2 and NOx emissions released into the air react with water vapor and other chemicals to form acids that fall back to Earth. Power plants burning coal and heavy oil produce over two-thirds of the annual SO2 emissions in the US. About 40% of NOx emissions are from power plants. Around 10% is emitted from various sources like industrial and commercial boilers.

The Cap and Trade Basics to Reduce Air Emissions

The Acid Rain Program was the first national cap and trade program in the country and introduced a system of allowance trading that uses market-based incentives to reduce pollution. This allows flexibility to select the most cost-effective approach to reducing emissions. Read more about the Cap and Trade Basics.

cap and trade program between two plants for air emissions regulations at the EPA

What is the EPA 40 CFR Part 75 Regulation?

The EPA 40 CFR Part 75 rule was created to establish requirements for monitoring and recordkeeping of air pollutants emitted from electric generating units (EGU) in support of the Acid Rain Program (ARP). The Part 75 regulations consist of eight subparts based on the purpose and applicability of the regulation, requirements relevant to each pollutant, missing data procedures, certification and recertification requirements, and recordkeeping and reporting policies.


Get ready for your Part 75 audits with ESC Spectrum’s useful guide and checklists for each part of the air emissions compliance process. This 40-page guide covers every part of the air emissions monitoring process, from QA/QC plans to DAS software to ECMPS and much more. This document provides P75 Audit Preparation Guidelines in the form of checklists to help prepare a facility for an actual or official audit without digging into the deep details of an actual audit. 


Part 75 also includes ten appendices that highlight CEMS requirements and data calculation guidelines based on pollutant and fuel type. The appendices of Part 75 break down specific requirements for CEMS and guidelines for calculating and estimating emissions data. Appendix D and E specify the methodology and protocol of emissions monitoring depending on the fuel type fired by an EGU (coal, gas, or oil). In Appendix A, you will find several references to periodically reviewing the span and range settings for the SO2 (§, NOx (§, CO2 (§, and flow (§ systems. Review these sections of Appendix A carefully to understand what additional changes need to be made fully, such as updating the Monitoring Plan records triggered by changing the MPCs, the MEC, or spend and range settings. 


Read our blog post about Breaking Down Part 75 Appendix A Span and Range Equipment Specifications to see why span and range settings are important and how they might affect your linearity checks.


Did you know that emission sources that follow the Part 75 emissions monitoring and reporting requirements must procure Environmental Protection Agency protocol gases from a production site that is listed as a Protocol Gas Verification Program (PGVP) participant on the date that the gases are procured or from a vendor who sells unaltered EPA protocol gases from PGVP-approved production site? The Protocol Gas Verification Program (PGVP) was established in March 2011 and is designed to ensure the accuracy of calibration gases.


Part 75 is referenced in several other core Acid Rain rules and also interfaces with parts of the New Source Performance Standards (NSPS) in 40 CFR Part 60. 

What is the EPA 40 CFR Part 60 Regulation?

40 CFR Part 60 regulations, otherwise known as New Source Performance Standards (NSPS), are pollution control standards issued by the U.S. Environmental Protection Agency. Adherence to these performance standards maintains the air quality in an area or region by reducing or eliminating pollutants’ release. The EPA classifies each U.S. county’s status as in “attainment” or “non-attainment” for each of the NSPS standards. A geographic area with air quality that is cleaner than the primary standard is called an “attainment” area; areas that do not meet the primary standard are called “nonattainment” areas. This helpful Part 60 Monitoring guide is a useful starting point for understanding what the Part 60 regulation means for your facility. 


New Source Performance Standards (NSPS) establish emission limitations achievable through an application of the best available control technology (BACT) for categories of stationary air pollution sources. These standards for BACT vary and are based on the class, type, and size of the source. The stationary sources subject to NSPS are required to perform an initial performance test to demonstrate compliance. This sometimes requires sources to install continuous emission monitors.


The EPA permits “attainment” counties’ new or modified sources to operate in such a manner that maintains attainment and avoids “non-attainment.” The agency regulates the “non-attainment” counties’ sources to reduce emissions to achieve attainment status within several years. The Part 60 regulations consist of various subparts based on the business sector or industrial group, the type of emission source, fuel combusted, and pollution control equipment.


There are six common air pollutants also known as criteria pollutants. These pollutants are found all over the U.S. They can harm your health and the environment and cause property damage.


The pollutants are:

  • particulate matter

  • photochemical oxidants (including ozone)

  • carbon monoxide

  • sulfur oxides

  • nitrogen oxides

  • lead


The EPA works with state governors to identify “nonattainment” areas where the air does not meet allowable limits for a common air pollutant. States develop plans (SIDs) to reduce air pollutants at allowable levels at power plants. Many clean-up requirements for particle pollution include large industrial sources such as power plants, chemical processing, and petroleum refineries.


In 2007, the Environmental Protection Agency (EPA) modified the definition of chemical process plants and how ethanol plants are categorized affecting ethanol regulations for CEM systems.


Before the 2007 EPA’s rule changes, corn milling facilities that produced only ethanol for fuel use were considered chemical process plants, unlike facilities that produced ethanol for human consumption.


The result of this rule change is ethanol plants, regardless of what the ethanol is produced for, must demonstrate compliance with various air quality emission standards as it applies to three Clean Air Act permitting programs. Read more about the Ethanol Regulations in the CEMS world in The Source.


Learn more about the activities required under 40 CFR Part 60 in our blog post Air Quality Compliance Reporting. Facilities that must comply with 40 CFR Part 60 and 40 CFR Part 63 are required to submit reports to the EPA on a quarterly, semiannual and annual basis. At the end of the reporting period, the facility has 30 calendar days to prepare and submit the required report under the signature of the Responsible Official for the facility.

What is the EPA 40 CFR Part 63 Regulation?

The Environmental Protection Agency’s 40 CFR Part 63 regulations emissions standards (NESHAP) are for hazardous air pollutants not covered by National Ambient Air Quality Standards (NAAQS) and emitted from natural and human-made sources, including volcanoes, wildfires, motor vehicles, industrial facilities, and oil refineries.


They are considered toxic compared to other air pollutants because exposure to them at a sufficient concentration and duration is known or suspected to increase the risk of specific health problems. These include cancer, heart disease, respiratory illness, and reduced fertility.


The standards for a particular source category require the maximum degree of emission reduction that the EPA determines to be achievable, known as the Maximum Achievable Control Technology (MACT) standards. 


On February 28, 2022, the Environmental Protection Agency lifted an 18-year stay on formaldehyde air emissions for two types of stationary combustion turbines. The EPA has identified stationary combustion turbines as major sources of hazardous air pollutants (HAP) emissions such as formaldehyde, toluene, benzene, and acetaldehyde. Read more about the updates on 40 CFR 63 Subpart YYYY including changes, who is subject to YYYY, facility limits, and more.

Updates to Air Emissions Regulations in the Past Years

In 2005, the Clean Air Mercury Rule, which is now vacated, and the Clean Air Interstate Rule (CAIR) were instated. The Clean Air Act Interstate Rule ended in 2014 and was replaced by the Cross-State Pollution Rule (CSAPR) promoting the usage of cleaner fuels and introducing NOX and SO2 control technology.

Greenhouse Gas (GHG) Emissions Compliance


In 2007, the Supreme Court ruled that GHGs were covered by the Clean Air Act and could be regulated if determined to be a danger to human health. The Final Rule for Mandatory Reporting of Greenhouse Gases was published in 2009. Starting March 10, 2009, Mandatory GHG Reporting was required. The proposed rule requires suppliers of fossil fuels or industrial greenhouse gases that emit 25,000 metric tons or more of GHG emissions per year to submit reports annually to the EPA. Learn more about Greenhouse Gas (GHG) emissions and how using a Data Acquisition System can help you stay in compliance.


Mercury and Air Toxics Standards

In 2011, Mercury and Air Toxics Standards also referred to as MATS was implemented for reporting to start in 2015. The EPA set technology-based emissions standards for mercury and other HAP emitted by the Coal- and Oil-Fired Electric Utility Steam Generating Units (EGUs) with a capacity of more than 25 megawatts. The CAA requires the EPA to regulate Hazardous Air Pollutants (HAPs) from large industrial facilities known as major sources in two phases. The first phase is “technology-based.” The EPA develops standards for controlling emissions of air toxics from sources in a specific industry group. These MACT standards are based on emission levels that are already in place by the controlled and low-emitting sources in the industry. The second phase is “risk-based” called residual risk. This is when the EPA determines whether more health-protective standards are necessary.


On September 9, 2020, the U.S. Environmental Protection Agency (EPA) published the final changes to the Mercury and Air Toxins Standards (MATS) limiting the allowable amount of mercury (Hg) and other pollutants from coal and coal-fired power plants. The MATS revisions from September 2020 will take mandatory effect in 2024. 


The EPA announced on January 31, 2022, the 2012 Mercury and Air Toxin Standards (MATS) for power plants. The announcement proposes to revoke a reconsideration step made by the agency in May 2020 and affirms that it is appropriate and necessary to regulate hazardous pollutants for coal and oil-fired electric generating units (EGUs). Learn more about MATS and the proposed changes.


Cross-State Air Pollution Rule

On July 6, 2011, the EPA finalized the Cross-State Air Pollution Rule replacing the Clean Air Act Interstate Rule (CAIR) to address air pollution from upwind states that cross state lines and affects the air quality in downwind states. This rule requires fossil fuel-fired electric generating units at gas-, coal-, and oil-fired facilities in 27 states. This rule requires states in the eastern half of the U.S. to improve air quality by reducing and monitoring power plant emissions that cross state lines. The CSAPR implementation began on January 1, 2015.


On April 6, 2022, EPA proposed a FIP addressing interstate transport for the 2015 ozone National Ambient Air Quality Standards (NAAQS). Comments on the Plan were due June 6, 2022. The proposed plan changes are based on EPA findings of 36 nonattainment and maintenance problems throughout the country. It also would establish a revised CSAPR ozone season Group 3 NOx emissions trading program for EGU in 25 states, backstop daily emission rate limitations for certain coal-fired EGUs, and unit-specific NOx emission rate limits for certain non-EGU industrial emissions units. Read more about what these proposed changes mean and their effect on plants.

Operating Permits for Your Facility

Air operating permits are legally enforceable documents that are designed to improve compliance by outlining and clarifying what facilities must do to control air pollution. Title V Operating Permits must be renewed every five years. Depending on your permit requirements, you may need to monitor emissions by the hour or even by the minute. In this case, a CEMS would be necessary for compliance. ESC Spectrum can help you comply with your Title V Permit at every step of the way with a full suite of CEMS and DAS products and services.

Air Emissions Regulations Most Applicable to ESC Spectrum

ESC Spectrum serves almost any industry with a facility that burns fossil fuel from electrical utilities, petrochemical refineries, and chemical processors to biowaste incinerators.


Our Regulatory experts created Air Emissions Regulations 101 to help educate our new team members.  It’s a great starting point for anyone new to the air emissions monitoring and compliance industry. for an overview of EPA regulatory history, the similarities, and differences between Part 60, 63, and 75, as well as how ESC Spectrum helps facilities with their compliance and monitoring activities.

Part 60 New Source Performance Standards for Stationary Sources

key for part 60 subparts

Part 63 National Emission Standards for HAPs for Source Categories

key for subparts for part 63

Helpful Resources for Your Facility's Air Emissions Compliance

In-house procedures for NOx Correlation Testing required by the EPA

High levels of NOx can have a negative effect on vegetation by making it more susceptible to disease and frost damage.

Recommended Monitoring Plan Checklists

When you have and use in-house procedures, checklists, QA/QC plans, and other organizational aids, you can achieve greater consistency and perform your tasks more efficiently.

Quick checklist to prepare and pass a CEMS audit

Failed calibrations or questionable data for CO2 audits, flow-to-load or heat input changes, reporting errors, late quarterly reports, or be part of an EPA, state, or annual compliance review?