Aaron represents clients in major environmental litigation and regulatory matters across the country, including nearly every significant proceeding involving the Environmental Protection Agency’s Regional Haze Program. As a leader of the firm’s visibility practice, Aaron has been called upon to testify before the US House of Representatives. Aaron has also litigated significant visibility rules before numerous federal courts of appeals, arguing most recently before the Ninth Circuit. Aaron’s climate change work has involved every significant EPA rulemaking action since the US Supreme Court’s decision in Massachusetts v. EPA. He has, for instance, helped clients develop their responses and find creative solutions in response to EPA’s Endangerment Finding, its mobile source rules, and the Clean Power Plan for existing electric generating facilities.