Mack focuses his practice on all aspects of the Clean Air Act. He helps clients obtain needed permits, solve compliance challenges, participate in rule and policy making activities, and minimize enforcement risk. In doing so, he helps bridge the gap often found between legal requirements and technical realities. Mack has practiced almost exclusively in the area of air law since starting his practice in 2003.

For more than 20 years, Mack has represented electric utility, landfill, manufacturing, and other industrial clients in connection with important air quality issues arising out of federal and state regulations governing the construction and operation of stationary sources of air emissions. He also has extensive experience in litigation over air regulations. Mack has represented his clients’ interests in many of the most significant air law cases over the last decade, including successful challenges to the New Source Review Tailoring Rule, the Mercury and Air Toxics Standards, and the Clean Power Plan.

Mack has direct and extensive experience with the most controversial Clean Air Act programs, including:

• New Source Review/Prevention of Significant Deterioration (NSR/PSD)
• National Ambient Air Quality Standards (NAAQS)
• Title V Operating Permits and Petitions to Object
• Regional Haze/Best Available Retrofit Technology (BART)
• New Source Performance Standards (NSPS)
• National Emission Standards for Hazardous Air Pollutants (NESHAP) & Maximum Achievable Control Technology (MACT) Standards

In addition, Mack has assisted numerous clients with lesser-known Clean Air Act programs, including those that regulate ozone-depleting substances used in refrigerant appliances, hazardous air pollutants emitted by reciprocating internal combustion engines, and nonhazardous secondary materials combustion.

• Represented a trade association in litigation over the Clean Power Plan repeal and adoption of the Affordable Clean Energy (ACE) rule in the D.C. Circuit.
• Conducted independent investigation of the Colorado minor source air permitting program in response to whistleblower complaints about air dispersion modeling practices.
• Advised ethylene oxide manufacturers and users in air permitting and enforcement actions arising out of EPA’s decision to issue new risk values for ethylene oxide in 2016.
• Litigated an EPA action to disapprove a southwestern state’s implementation plan for regional haze and adopt a federal plan, which included making oral argument on behalf of the state to the U.S. Court of Appeals for the Ninth Circuit.
• Assisted coal and utility interests in successful petitions for certiorari to the U.S. Supreme Court challenging EPA’s mercury and climate change regulations for the electric utility sector.
• Advised numerous large electric utility companies across the U.S. on potential NSR implications for all capital and significant maintenance projects.
• Assisted a glass manufacturer in obtaining a PSD permit for a new facility.
• Represented a biomass power facility in responding to an objection to its Title V permit granted by EPA, including coordination with the state permitting authority to resolve that objection through permit revisions.
• Advised a large landfill company regarding the potential permitting implications of purchasing, installing, modifying, or reconstructing landfill gas flares and landfill gas-to-energy projects.
• Advised numerous clients in response to EPA information requests issued under Section 114 of the Clean Air Act.
• Assisted coal and utility interests in commenting on EPA’s Clean Power Plan and represented those interests in challenging the rule in the D.C. Circuit.

• Chambers USA: Environment, Georgia (2023-2025)
• Legal 500 United States for Environment: Litigation and Environment: Regulatory (2021-2025)
• Rising Star in Environmental, Law & Politics’ Georgia Super Lawyers and Atlanta Magazine (2007, 2009, 2011-2016)
• Best Lawyers in America®: Environmental Law (2016-2026)