A brief look at the Clean Air Act along with a commercially available GC reactor system for testing NMOC in accordance with EPA Method 25C

Landfills and solid waste management have significantly changed since the 1950s. 1950s was a time when your trash was simply called rubbish and left to sit in an open pile. Flies were one of the major concerns at the time.

The Clean Air Act of 1963 is a US federal law designed to set limits on air pollution for the national level. It was a groundbreaking environmental regulation that gave a comprehensive overview on standards required to keep the air safe and clean from pollutants.

There were major amendments to the Clean Air Act and Air Quality Act in 1970s and 1990s. In the 1990s, emissions from solid waste disposal via incinerators began to have guidelines. These guidelines included using the best available commercial technology (BACT) for greenhouse gas emissions of new sources or modified emissions units for solid waste disposal. It was not until an additional amendment in 1996 that expanded the purview of Title V permits to include Municipal Solid Waste landfills. The official Federal Register Document is 96-5529. These combined acts from the 1990s led to a 38.1% decrease in methane emissions from solid waste disposal [1]. It is in this document that the EPA makes the official determination that municipal solid waste landfills have a reasonable cause of danger to public health or welfare under statues from the Clean Air Act. The major emission of concern is non-methane organic compounds (NMOC) and methane. NMOC is a general term that encompasses pollutants, hazardous compounds, and volatile organic compounds. There are approximately 1,250 landfills in the U.S. that fall under this regulation which require new source and operational permits [2]. With the concern of NMOC contaminants, the amendment included EPA Methods 3C and 25C to expand analytical techniques for measuring carbon dioxide, methane, nitrogen, oxygen, and NMOC in landfill gases or stationary samples.

EPA Method 25C for NMOC analysis requires the usage of a two-step reactor. The GC effluent is initially combusted to CO2 with an oxidation catalyst and then is reduced to methane via a reduction catalyst [3]. When this method was introduced, analytical chemist had to devise homemade reactors to run the technique. The Polyarc System is a commercially available reactor system that will fully convert landfill gases to methane. A major benefit is the usage of improved catalyst that is more tolerant to potential catalyst poisons found in samples. This leads to longer uptime, while also having easier catalyst replacements.  

By: Connor Beach, Technical Sales Engineer
Q1 2023


[1]. United Nations Framework Convention on Climate Change. Query results for — Parties: United States of America and Annex I — Years: 1990 and Last Inventory Year (2020) — Category: 5.A.1 Managed Waste Disposal Sites — Unit: kt CO₂ equivalent. https://di.unfccc.int/comparison_by_gas. (accessed Jan 13, 2023).

[2]. Ian Tise; Number of U.S. landfill facilities in 2018, by region, 2022. Statista.  https://www.statista.com/statistics/186346/number-of-landfills-in-us-municipal-solid-waste/. (accessed Jan 13, 2023).

[3]. METHOD 25—DETERMINATION OF TOTAL GASEOUS NONMETHANE ORGANIC EMISSIONS AS CARBON, 2017. Environmental Protective Agency Web site. https://www.epa.gov/sites/default/files/2017-08/documents/method_25.pdf. (accessed Jan 13, 2023).