Documentation of the Evaluation of CALPUFF and Other Long ...
Documentation of the Evaluation of CALPUFF and Other Long ... Documentation of the Evaluation of CALPUFF and Other Long ...
1.0 INTRODUCTION Dispersion models, such as the Industrial Source Complex Short Term (ISCST; EPA, 1995) or American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD; EPA, 2004; 2009c) typically assume steady‐state, horizontally homogeneous wind fields instantaneously over the entire modeling domain and are usually limited to distances of less than 50 kilometers from a source. However, dispersion model applications of distances of hundreds of kilometers from a source require other models or modeling systems. At these distances, the transport times are sufficiently long that the mean wind fields cannot be considered steady‐state or homogeneous. As part of the Prevention of Significant Deterioration (PSD) program, new sources or proposed modifications to existing sources may be required to assess the air quality and Air Quality Related Values (AQRVs) impacts at Class I and sensitive Class II areas that may be far away from the source. AQRVs include visibility and acid (sulfur and nitrogen) deposition. There are 156 federally mandated Class I areas in the U.S. that consist of National Parks, Wilderness Areas and Wildlife Refuges that are administered by Federal Land Managers (FLMs) from the National Park Service (NPS), United States Forest Service (USFS) and Fish and Wildlife Service (FWS), respectively. Thus, non‐steady‐state Long Range Transport (LRT) dispersion models are needed to address air quality and AQRVs issues at distances beyond 50 km from a source. 1.1 BACKGROUND The Interagency Workgroup on Air Quality Modeling (IWAQM) was formed to provide a focus for the development of technically sound recommendations regarding assessment of air pollutant source impacts on Federal Class I areas. Meetings were held with personnel from interested Federal agencies, including the Environmental Protection Agency (EPA), the USFS, NPS and FWS. The purpose of these meetings was to review respective modeling programs, to develop an organizational framework, and to formulate reasonable objectives and plans that could be presented to management for support and commitment. One objective of the IWAQM is the recommendation of LRT dispersion models for assessing air quality and AQRVs at Class I areas. One such LRT dispersion model is the CALPUFF modeling system (Scire et al., 2000b). The CALPUFF modeling system consists of several components: (1) CALMET (Scire et al., 2000a), a meteorological preprocessor that can use as input surface, upper air, and/or on‐site meteorological observations and/or prognostic meteorological model output data to create a three‐dimensional wind field and derive boundary layer parameters based on gridded land use data; (2) CALPUFF, a Lagrangian puff dispersion model that can simulate the effects of temporally and spatially varying meteorological conditions on pollutant transport, remove pollutants through dry and wet deposition processes, and includes limited ability to transform pollutant species through chemical reactions; and (3) CALPOST, a postprocessor that takes the hourly estimates from CALPUFF and generates n‐hr estimates as well as tables of maximum values. In 1998, EPA published the report entitled “A Comparison of CALPUFF Modeling Results to Two Tracer Field Experiments” (EPA‐454/R‐98‐009) (EPA, 1998a). The 1998 EPA study examined concentration estimates from the CALPUFF dispersion model that were compared to observed tracer concentrations from two short term field experiments. The first experiment was at the Savannah River Laboratory (SRL75) in South Carolina in December 1975 (DOE, 1978) and the second was the Great Plains experiment (GP80) near Norman, Oklahoma (Ferber et al., 1981) in 1
July 1980. Both experiments examined long‐range transport of inert tracer materials to demonstrate the feasibility of using other tracers as alternatives to the more commonly used sulfur hexafluoride (SF6). Several tracers were released for a short duration (3‐4 hours) and the resulting plume concentrations were recorded at an array of monitors downwind from the source. For the SRL75 field experiment, monitors were located approximately 100 kilometers from the source. For the Great Plains experiment, arcs of monitors were located 100 and 600 kilometers from the source. In 1998, IWAQM released their Phase 2 recommendations in a report “Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary Report and Recommendations for Modeling Long Range Transport Impacts” (EPA, 1998b 7 ). These recommendations included a screening and refined LRT modeling approach based on the CALPUFF modeling system. The IWAQM recommendations were based in part on the 1998 EPA tracer test CALPUFF evaluation. It was IWAQM’s conclusion at the time that it was not possible to prescribe all of the decisions needed in a CALPUFF/CALMET application: “The control of the CALMET options requires expert understanding of mesoscale and microscale meteorological effects on meteorological conditions, and finesse to adjust the available processing controls within CALMET to develop the desired effects. The IWAQM does not anticipate the lessening in this required expertise in the future” (EPA, 1998b). On April 15, 2003, EPA issued a “Revision to the Guideline on Air Quality Models: Adoption of a Preferred Long Range Transport Model and Other Revisions” in the Federal Register (EPA, 2003 8 ) that adopted the CALPUFF model as the EPA‐recommended (Appendix W) model for assessing the far‐field (> 50 km) air quality impacts due to chemically inert pollutants. In 2005, EPA issued another revision to the air quality modeling guidelines that recommended the AERMOD steady‐state Gaussian plume model be used for near‐source air quality issues. Thus, from 2005 on to present, there are two EPA‐recommended models to address air quality issues due to primary pollutants: AERMOD for near‐source (< 50 km) assessments; and CALPUFF for far‐field (> 50 km) assessments. In 2005, EPA formed a CALPUFF workgroup to help identify issues with the existing 1998 IWAQM guidance. In response to this, EPA initiated reevaluation of the CALPUFF system to update the 1998 IWAQM Phase 2 Recommendations. In May 2009, EPA released a draft document entitled the “Reassessment of the Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary Report: Revisions to the Phase 2 Recommendations” (EPA, 2009a). In this document, EPA described the developmental status of the CALPUFF modeling system. CALPUFF has evolved continuously since the publication of the original 1998 IWAQM Phase 2 recommendations; however, the status of CALPUFF related guidance has not kept pace with the developmental process. The May 2009 IWAQM Phase 2 Reassessment Report noted that “The required expertise and collective body of knowledge in mesoscale meteorological models has never fully emerged from within the dispersion modeling community to support the necessary expert judgment on selection of CALMET control options” (EPA, 2009a). In regards to the 1998 IWAQM Phase 2 lack of prescribing recommended CALMET settings, the May 2009 IWAQM Phase 2 Reassessment Report states: “In a regulatory context, this situation has often resulted in an ‘anything goes’ process, whereby model control option selection can be leveraged as an instrument to achieve a desired modeled outcome, 7 http://www.epa.gov/scram001/7thconf/calpuff/phase2.pdf 8 http://www.federalregister.gov/articles/2003/04/15/03‐8542/revision‐to‐the‐guideline‐on‐air‐quality‐models‐ adoption‐of‐a‐preferred‐long‐range‐transport‐model 2
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July 1980. Both experiments examined long‐range transport <strong>of</strong> inert tracer materials to<br />
demonstrate <strong>the</strong> feasibility <strong>of</strong> using o<strong>the</strong>r tracers as alternatives to <strong>the</strong> more commonly used<br />
sulfur hexafluoride (SF6). Several tracers were released for a short duration (3‐4 hours) <strong>and</strong> <strong>the</strong><br />
resulting plume concentrations were recorded at an array <strong>of</strong> monitors downwind from <strong>the</strong><br />
source. For <strong>the</strong> SRL75 field experiment, monitors were located approximately 100 kilometers<br />
from <strong>the</strong> source. For <strong>the</strong> Great Plains experiment, arcs <strong>of</strong> monitors were located 100 <strong>and</strong> 600<br />
kilometers from <strong>the</strong> source.<br />
In 1998, IWAQM released <strong>the</strong>ir Phase 2 recommendations in a report “Interagency Workgroup<br />
on Air Quality Modeling (IWAQM) Phase 2 Summary Report <strong>and</strong> Recommendations for<br />
Modeling <strong>Long</strong> Range Transport Impacts” (EPA, 1998b 7 ). These recommendations included a<br />
screening <strong>and</strong> refined LRT modeling approach based on <strong>the</strong> <strong>CALPUFF</strong> modeling system. The<br />
IWAQM recommendations were based in part on <strong>the</strong> 1998 EPA tracer test <strong>CALPUFF</strong> evaluation.<br />
It was IWAQM’s conclusion at <strong>the</strong> time that it was not possible to prescribe all <strong>of</strong> <strong>the</strong> decisions<br />
needed in a <strong>CALPUFF</strong>/CALMET application: “The control <strong>of</strong> <strong>the</strong> CALMET options requires expert<br />
underst<strong>and</strong>ing <strong>of</strong> mesoscale <strong>and</strong> microscale meteorological effects on meteorological<br />
conditions, <strong>and</strong> finesse to adjust <strong>the</strong> available processing controls within CALMET to develop <strong>the</strong><br />
desired effects. The IWAQM does not anticipate <strong>the</strong> lessening in this required expertise in <strong>the</strong><br />
future” (EPA, 1998b).<br />
On April 15, 2003, EPA issued a “Revision to <strong>the</strong> Guideline on Air Quality Models: Adoption <strong>of</strong> a<br />
Preferred <strong>Long</strong> Range Transport Model <strong>and</strong> O<strong>the</strong>r Revisions” in <strong>the</strong> Federal Register (EPA,<br />
2003 8 ) that adopted <strong>the</strong> <strong>CALPUFF</strong> model as <strong>the</strong> EPA‐recommended (Appendix W) model for<br />
assessing <strong>the</strong> far‐field (> 50 km) air quality impacts due to chemically inert pollutants. In 2005,<br />
EPA issued ano<strong>the</strong>r revision to <strong>the</strong> air quality modeling guidelines that recommended <strong>the</strong><br />
AERMOD steady‐state Gaussian plume model be used for near‐source air quality issues. Thus,<br />
from 2005 on to present, <strong>the</strong>re are two EPA‐recommended models to address air quality issues<br />
due to primary pollutants: AERMOD for near‐source (< 50 km) assessments; <strong>and</strong> <strong>CALPUFF</strong> for<br />
far‐field (> 50 km) assessments.<br />
In 2005, EPA formed a <strong>CALPUFF</strong> workgroup to help identify issues with <strong>the</strong> existing 1998<br />
IWAQM guidance. In response to this, EPA initiated reevaluation <strong>of</strong> <strong>the</strong> <strong>CALPUFF</strong> system to<br />
update <strong>the</strong> 1998 IWAQM Phase 2 Recommendations.<br />
In May 2009, EPA released a draft document entitled <strong>the</strong> “Reassessment <strong>of</strong> <strong>the</strong> Interagency<br />
Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary Report: Revisions to <strong>the</strong> Phase<br />
2 Recommendations” (EPA, 2009a). In this document, EPA described <strong>the</strong> developmental status<br />
<strong>of</strong> <strong>the</strong> <strong>CALPUFF</strong> modeling system. <strong>CALPUFF</strong> has evolved continuously since <strong>the</strong> publication <strong>of</strong><br />
<strong>the</strong> original 1998 IWAQM Phase 2 recommendations; however, <strong>the</strong> status <strong>of</strong> <strong>CALPUFF</strong> related<br />
guidance has not kept pace with <strong>the</strong> developmental process. The May 2009 IWAQM Phase 2<br />
Reassessment Report noted that “The required expertise <strong>and</strong> collective body <strong>of</strong> knowledge in<br />
mesoscale meteorological models has never fully emerged from within <strong>the</strong> dispersion modeling<br />
community to support <strong>the</strong> necessary expert judgment on selection <strong>of</strong> CALMET control options”<br />
(EPA, 2009a). In regards to <strong>the</strong> 1998 IWAQM Phase 2 lack <strong>of</strong> prescribing recommended<br />
CALMET settings, <strong>the</strong> May 2009 IWAQM Phase 2 Reassessment Report states: “In a regulatory<br />
context, this situation has <strong>of</strong>ten resulted in an ‘anything goes’ process, whereby model control<br />
option selection can be leveraged as an instrument to achieve a desired modeled outcome,<br />
7 http://www.epa.gov/scram001/7thconf/calpuff/phase2.pdf<br />
8 http://www.federalregister.gov/articles/2003/04/15/03‐8542/revision‐to‐<strong>the</strong>‐guideline‐on‐air‐quality‐models‐<br />
adoption‐<strong>of</strong>‐a‐preferred‐long‐range‐transport‐model<br />
2