title: Assessing methods to estimate emissions of non-methane organic compounds from landfills.
abstract: The non-methane organic compound (NMOC) emission rate is used to assess compliance with landfill gas emission regulations by the United States Environmental Protection Agency (USEPA). A recent USEPA Report (EPA/600/R-11/033) employed a ratio method to estimate speciated NMOC emissions (i.e., individual NMOC emissions): speciated NMOC emissions=measured methane (CH4) emission multiplied by the ratio of individual NMOCs concentration relative to CH4 concentration (C(NMOCs)/C(CH4)) in the landfill header gas. The objectives of this study were to (1) evaluate the efficacy of the ratio method in estimating speciated NMOC flux from landfills; (2) determine for what types of landfills the ratio method may be in error and why, using recent field data to quantify the spatial variation of (C(NMOCs)/C(CH4)) in landfills; and (3) formulate alternative models for estimating NMOC emissions from landfills for cases in which the ratio method results in biased estimates. This study focuses on emissions through landfill covers measured with flux chambers and evaluates the utility of the ratio method for estimating NMOC emission through this pathway. Evaluation of the ratio method was performed using CH4 and speciated NMOC concentration and flux data from 2012/2013 field sampling of four landfills, an unpublished landfill study, and literature data from three landfills. The ratio method worked well for landfills with thin covers (<40 cm), predicting composite NMOC flux (as hexane-C) to within a factor of 10× for 13 out of 15 measurements. However, for thick covers (⩾40 cm) the ratio method overestimated NMOC emissions by ⩾10× for 8 out of 10 measurements. Alternative models were explored incorporating other chemical properties into the ratio method. A molecular weight squared (MW)(2)-modified ratio equation was shown to best address the tendency of the current ratio method to overestimate NMOC fluxes for thick covers. While these analyses were only performed using NMOC fluxes through landfill covers measured with flux chambers, results indicate the current USEPA approach for estimating NMOC emissions may overestimate speciated NMOC emission ⩾10× for many compounds.
authors.affiliation: Department of Civil and Environmental Engineering, University of Delaware, 301 DuPont Hall, Newark, DE 19716, USA. Electronic address: jmsaquing@gmail.com.
authors.forename: Jovita M
authors.initials: JM
authors.lastname: Saquing
authors.affiliation: Department of Earth Ocean and Atmospheric Science, Florida State University, Tallahassee, FL 32306-4320, USA. Electronic address: jchanton@fsu.edu.
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Chanton
authors.affiliation: Yolo County Planning & Public Works Department, Division of Integrated Waste Management, Woodland, CA 95776, USA. Electronic address: Ramin.Yazdani@yolocounty.org.
authors.forename: Ramin
authors.initials: R
authors.lastname: Yazdani
authors.affiliation: Department of Civil, Construction, and Environmental Engineering, Box 7908, North Carolina State University, Raleigh, NC 27695-7908, USA. Electronic address: barlaz@eos.ncsu.edu.
authors.forename: Morton A
authors.initials: MA
authors.lastname: Barlaz
authors.affiliation: Department of Environmental Engineering, Miljovej-Building 113, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark. Electronic address: chas@env.dtu.dk.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Scheutz
authors.affiliation: Department of Chemistry, 570 Rowland Hall, University of California, Irvine, CA 92697-2025, USA. Electronic address: drblake@uci.edu.
authors.forename: Don R
authors.initials: DR
authors.lastname: Blake
authors.affiliation: Department of Civil and Environmental Engineering, University of Delaware, 301 DuPont Hall, Newark, DE 19716, USA. Electronic address: imhoff@udel.edu.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Imhoff
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D008962:Models, Theoretical; D009930:Organic Chemicals / Q000032:analysis*; D014481:United States; D014484:United States Environmental Protection Agency; D064091:Waste Disposal Facilities
chemical_list: D000393:Air Pollutants; D009930:Organic Chemicals
keywords: Field measurement; Landfill gas emission; NMOC emission; NMOC flux estimation