MARAMA has conducted projects to better understand sources of air toxics and to assess the costs and benefits of emission control measures.

  • MARAMA Fumigation Workgroup (Members Only) MARAMA manages the members workgroup to share information and practices concerning Fumigation in the region.
  • Emerging Pollutants Workgroup (Members Only)  MARAMA convenes a monthly members workgroup to share information and practices to manage emerging pollutants such as Art Glass, PFAS/PFOA, and Ethylene Oxide in the region.

Technical Assistance to MARAMA on EPA Cumulative Exposure Project (CEP): Review of Air Toxics Modeling, January 1999, P.T. Roberts, H.H. Main, S.B. Hurwitt, Sonoma Technology, Inc.

EPA’s Cumulative Exposure Project toxics modelingwere reviewed.  Model-estimated concentrations for 1990 of toxic air pollutants were compared with 1996 ambient concentrations in Philadelphia, New Brunswick (NJ), and Baltimore.  Ambient data is from PAMS monitoring sites, which only operate during the summer, while the model estimates are annual averages. Morning data was compared, because a comparison of summer morning data to 24-hour, year-round canister data for 8 HAPs at Philadelphia showed good agreement.  It should be noted that the modeling methods used at the time this report was prepared are not necessarily the same as modeling methods currently used by EPA.  Three overall issues were identified in reviewing EPA’s modeling:

  • It is inappropriate to rely on model results at the census-tract level. The model is only reliable over larger areas.
  • Expected model performance and uncertainty varies widely by pollutant. Hazardous Air Pollutant (HAP) vary in their emission, chemical reactivity, transport and dispersion, and background characteristics, and all these factors influence model performance.
  • EPA modeling guidance for dispersion models indicates that short-term concentrations should be within a factor of two of monitored values, and annual average model performance is expected to be better than short-term estimates. EPA’s own model performance evaluation performed as part of the CEP compared available ambient data for 19 HAPs with model results and found that 68% of the comparisons were within a factor of three. Sonoma raises the question of whether this is acceptable performance.

Sonoma’s comparison of monitored and modeled concentrations in Philadelphia, New Brunswick, and Baltimore led them to several conclusions, including those listed below. Of the HAPs investigated in this study, benzene, formaldehyde, and carbon tetrachloride are the most important with respect to cancer risk based on ambient data. Measured concentrations of these HAPs were well above cancer a risk benchmark of 1 in 1 million lifetime exposure risk.

  • Measured concentrations of species highly associated with motor vehicles (e.g., benzene, toluene, and xylenes) were typically within a factor of two or three of the model’s estimates. (The ambient concentration was usually lower than predicted by the model. This is consistent with recent studies showing that benzene has declined in the 1990s due to the use of reformulated gasoline.)
  • PAMS carbonyle compound concentrations were typically about twice those modeled. The model chemistry may be inadequate to reflect the secondary formation of carbonyles (e.g., formaldehyde).
  • Measured and modeled concentrations of methylchloride and carbon tetrachloride concentrations were similar and were typically at about the level the model assumed as a background concentration. (Data only for Philadelphia.)
  • Several differences between modeled and monitored concentrations may indicate problems with emissions factors or activity data used to estimate emissions:
    • Ethylene dibromide was monitored at 20 times the level predicted by the model. The model may be missing key sources. (Data only for Philadelphia.)
    • Measured ethylene dichloride was at least an order of magnitude lower than modeled. Emissions estimates may be overstated. (Data only for Philadelphia.)
  • Ambient variability in concentrations is often much greater than reflected in the model.
  • Some pollutants are measured at very low concentrations, near the detection limits, of monitoring equipment.

Delaware state-specific language applicable to HAP sources is included in Regulations1100 and 1138 as follows:

Delaware started with EPA Part 63 MACT/GACT standards applicable to area sources in Delaware and then revised them to be appropriate for Delaware. A couple of examples follow:

  • Sub M (Perc Dry Cleaning) – DE does not exempt coin-operated machines as EPA had done.
  • Sub T (Halogenated Solvent Cleaning) – DE included additional operating and design requirements that were already in place for degreasers under Regulation 1124.

Philadelphia AMS – Links to Philadelphia’s air toxics regulation and associated guidelines:

West Virginia – State Rule 34 adopts selected federal standards related to HAPs. State Rule 27 is for a specific list of toxic air pollutants that are HAPs. State Rule 13 has HAPs limits for permitting purposes.

Rule 13: https://dep.wv.gov/daq/small%20business/Documents/45CSR13_Final.pdf
Rule 27: https://dep.wv.gov/daq/planning/Documents/45-27.pdf
Rule 34: https://dep.wv.gov/daq/rulessummary/Documents/2018%20Final%20Rules/45CSR34_Final.pdf

Some state-specific information on WVDEP’s Division of Air Quality air toxics rules is below:

Maryland – MDE

Maryland state-specific language applicable to HAP sources is included in COMAR as follows: