title: Hybrid Modeling Approach to Estimate Exposures of Hazardous Air Pollutants (HAPs) for the National Air Toxics Assessment (NATA).
abstract: A hybrid air quality model has been developed and applied to estimate annual concentrations of 40 hazardous air pollutants (HAPs) across the continental United States (CONUS) to support the 2011 calendar year National Air Toxics Assessment (NATA). By combining a chemical transport model (CTM) with a Gaussian dispersion model, both reactive and nonreactive HAPs are accommodated across local to regional spatial scales, through a multiplicative technique designed to improve mass conservation relative to previous additive methods. The broad scope of multiple pollutants capturing regional to local spatial scale patterns across a vast spatial domain is precedent setting within the air toxics community. The hybrid design exhibits improved performance relative to the stand alone CTM and dispersion model. However, model performance varies widely across pollutant categories and quantifiably definitive performance assessments are hampered by a limited observation base and challenged by the multiple physical and chemical attributes of HAPs. Formaldehyde and acetaldehyde are the dominant HAP concentration and cancer risk drivers, characterized by strong regional signals associated with naturally emitted carbonyl precursors enhanced in urban transport corridors with strong mobile source sector emissions. The multiple pollutant emission characteristics of combustion dominated source sectors creates largely similar concentration patterns across the majority of HAPs. However, reactive carbonyls exhibit significantly less spatial variability relative to nonreactive HAPs across the CONUS.
authors: U.S. Environmental Protection Agency , Office of Air Quality Planning and Standards, Durham, North Carolina 27711, United States.
authors: Richard D
authors: RD
authors: Scheffe
authors: U.S. Environmental Protection Agency , Office of Air Quality Planning and Standards, Durham, North Carolina 27711, United States.
authors: Madeleine
authors: M
authors: Strum
authors: U.S. Environmental Protection Agency , Office of Air Quality Planning and Standards, Durham, North Carolina 27711, United States.
authors: Sharon B
authors: SB
authors: Phillips
authors: U.S. Environmental Protection Agency , Office of Air Quality Planning and Standards, Durham, North Carolina 27711, United States.
authors: James
authors: J
authors: Thurman
authors: U.S. Environmental Protection Agency , Office of Air Quality Planning and Standards, Durham, North Carolina 27711, United States.
authors: Alison
authors: A
authors: Eyth
authors: EC/R Incorporated , Chapel Hill, North Carolina 27514, United States.
authors: Steve
authors: S
authors: Fudge
authors: U.S. Environmental Protection Agency , Office of Air Quality Planning and Standards, Durham, North Carolina 27711, United States.
authors: Mark
authors: M
authors: Morris
authors: U.S. Environmental Protection Agency , Office of Air Quality Planning and Standards, Durham, North Carolina 27711, United States.
authors: Ted
authors: T
authors: Palma
authors: U.S. Environmental Protection Agency , Office of Transportation and Air Quality, Ann Arbor, Michigan 48105, United States.
authors: Richard
authors: R
authors: Cook
mesh_terms: D000393:Air Pollutants; D004784:Environmental Monitoring; D005557:Formaldehyde; D015386:Hazardous Substances; D006801:Humans; D008962:Models, Theoretical; D014481:United States
chemical_list: D000393:Air Pollutants; D015386:Hazardous Substances; D005557:Formaldehyde