Air Emissions from Combustion and Incineration Processes: Insights into Air Quality and US EPA Regulations

The escalating global generation of waste necessitates robust and environmentally sound management strategies. Among these, combustion and incineration processes play a crucial role in waste volume reduction and energy recovery. Nevertheless, these thermal treatment methods are significant sources of atmospheric pollutants, impacting air quality and public health. This review systematically examines air emissions from four major incineration types regulated under the U.S. Environmental Protection Agency’s (EPA) Clean Air Act (CAA) Sects. 111 (New Source Performance Standards [NSPS]) and 129 (National Emission Standards for Hazardous Air Pollutants [NESHAP]). These categories include Large Municipal Waste Combustors (LMWC), Hospital/Medical/Infectious Waste Incinerators (HMIWI), Commercial and Industrial Solid Waste Incineration (CISWI), and Sewage Sludge Incineration (SSI). This paper details the characteristic air pollutants emitted from these processes, evaluates the effectiveness of current air pollution control (APC) technologies, and compares emission concentrations and efficiencies across these systems and against global standards. This review highlights emerging pollutants, unregulated precursors, and persistent challenges related to insufficient emission controls during startup and shutdown phases. Furthermore, the review critically analyzes existing regulatory inconsistencies and blind spots within the U.S. framework. It also includes a discussion on public perception, co-incineration practices, and future research needs. This comprehensive analysis aims to clarify regulatory inconsistencies under U.S. EPA frameworks, identify persistent blind spots in emission control practices—particularly during startup and shutdown phases—and highlight emerging pollutants that remain unregulated, thereby supporting more targeted policy development and advanced emission mitigation strategies.