Challenges and Implications of EPA’s Proposed National Ambient Air Quality Standard for Ground-Level Ozone and Legislative Hearing on S. 638, S. 751, and S. 640 June 3, 2015 Permalink: https://www.epw.senate.gov/public/index.cfm/2015/6/challenges-and-implications-of-epa-s-proposed-national-ambient-air-quality-standard-for-ground-level-ozone-and-legislative-hearing-on-s-638-s-751-and-s-640