Dispersion Modeling Guidance for Airports Addressing Local Air Quality Health Concerns (2017)

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4FAA’s Aviation Emissions and Air Quality Handbook (which is available for download on the FAA website) has three primary objectives: 1. To provide guidance, procedures, and methodologies appropriate for use in carrying out air quality assessments prepared in association with FAA-supported projects/actions; 2. To help ensure that these air quality assessments meet the requirements of the National Environmental Policy Act (NEPA), the federal Clean Air Act (CAA), and other relevant laws and regulations; and 3. To provide a process for users to determine when an air quality assessment is considered necessary, the type of analysis that is appropriate, and the level of effort that is warranted. The approach taken by the FAA handbook is broad in scope for air quality assessments, whereas ACRP Research Report 179 provides detailed information about airport dispersion mod- eling for airport staff with an interest in or responsibility for the impacts of airport emissions on air quality in the airport vicinity. More specifically, this guidebook presents information for selecting and using specific dispersion models to address local air quality health concerns. The AEDT is FAA’s required model for airport air quality analysis. Two key components of AEDT are the EDMS, which converts airport activity into an emissions inventory, and the Amer- ican Meteorological Society/Environmental Protection Agency (EPA) Regulatory Model, called AERMOD, which takes the emissions inventory and computes pollutant concentrations based on the dispersion of the pollutants from emission sources to receptor locations. AERMOD is a general-purpose dispersion model developed and maintained by EPA and commonly used for regulatory purposes. Other dispersion models have been developed, often for specific emission source types or special applications. Some dispersion models include atmospheric chemistry to track the changes to pollutant species over time. Some models use different approaches to rep- resent how pollutants are emitted from different sources and the movement of those pollutants through the environment. Some models focus on changes within a small area, such as an airport boundary, while others compute changes over a much larger region. No single approach is best for all applications. ACRP Research Report 179 describes four dispersion models and provides guidance for selecting the most appropriate dispersion model for a particular study based on model capabilities and limitations, data requirements unique to airports, pollutant(s) of con- cern, resource availability, and output requirements. The guidance presented in this document is based on a comparison of the performance of four dispersion models applied under the same conditions at the same airport. A common EDMS emissions inventory was used to provide the necessary inputs for each dispersion model. The basis for the model inputs came from a detailed emissions analysis of LAX that was conducted by the Los Angeles World Airports (LAWA) in 2011–2012. Table 1 summarizes the models evalu- ated for ACRP Project 02-58 and highlights important differences among the models. C h a p t e r 1 Introduction

Introduction 5 Chapter 2 provides the following information: • A primer on dispersion modeling, describing basic concepts of dispersion modeling, the phys- ical and meteorological effects that cause pollutants to disperse, and the regulatory context that motivates the need for dispersion modeling; • Summaries of the four dispersion models compared in this study; and • A decision tree for selecting a specific dispersion model for a particular study or application. Chapter 3 provides summaries of prior published studies that compared different dispersion models in airport air quality applications. These case studies illustrate some of the benefits, limitations, and qualitative differences among the dispersion models. Chapter 4 addresses differences in input data requirements for each model. EDMS and AERMOD have been developed cooperatively so that EDMS outputs are compatible with AERMOD input requirements. For the other dispersion models, some amount of conversion or transformation of the input data was required. Chapter 5 presents the model intercomparison. This chapter describes how the different mod- els compared on a range of factors such as high and low pollutant concentrations, model sensi- tivity, run time, and ease of use. Chapter 6 describes potential improvements to the models examined. Modeling results could be improved by modifying how sources are represented, use of meteorological data, incorpora- tion of atmospheric chemistry, and other factors. A glossary also is provided. A combined Bibliography and References list follows the glossary. Model Platform Sources Aircraft Inputs Model Species Chemistry Met Inputs Output AERMOD (EDMS) Windows, Linux and GUI Aircraft, GSE, stationary sources Activity-based CO2, H2O, CO, VOC, NO2, NOx, SOx, PM10, PM2.5, air toxics 3 options for NO -> NO2 conversion AERMET using NWS, or user- defined Point based CALPUFF Windows, Linux User-defined User-defined CO, VOC, NOx, SOx, PM10, PM2.5, air toxics Simplified chemistry for secondary particle formation CALMET, MMIF or user-defined Point based SCICHEM Windows, Linux and GUI User-defined User-defined CO, VOC, NO2, NOx, SOx, O3, PM10, PM2.5, air toxics Detailed gas- phase and aerosol chemistry MMIF or user- defined Point based ADMS- Airport Windows GUI Aircraft (full LTO cycle), APU, GPU, GSE, engine startup, motor traffic, other (user-defined) General traffic information or individual traffic movements CO, VOC, NO2, NOx, SOx, O3, PM10, PM2.5, air toxics NO -> NO2 conversion; Limited O3 chemistry AERMET using NWS, or user- defined Point based Abbreviations: GUI = graphical user interface; GSE = ground support equipment; LTO = landing and take-off ; APU = auxiliary power unit; GPU = ground power unit; AERMET = a meteorological data preprocessor used in AERMOD; CALMET = a diagnostic meteorological model; MMIF = Mesoscale Model Interface Program; NWS = National Weather Service. Model species listed: CO = carbon monoxide; CO2 = carbon dioxide; H2O = water; NOx = nitrogen oxides, including NO (nitric oxide) and NO2 (nitrogen dioxide); O3 = ozone; PM10 = particulate matter of size 10 microns and below; PM2.5 = particulate matter of size 2.5 microns and below; SOx = sulfur oxides; VOCs = volatile organic compounds; and air toxics (pollutants deemed hazardous because they cause or may cause serious health effects or adverse environmental and ecological effects). Table 1. Summary of important aspects of four dispersion models evaluated in this study.