Quantifying Aircraft Lead Emissions at Airports (2015)

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Table 56 RVS Pb Emissions – Grams per Piston Operation ...........................................121 Table 57 RVS Pb Emissions – Percent by Mode .............................................................122 Table 58 RVS Pb Emissions – CY2011 Operations (Tons) ............................................122 Table 59 APA Pb Emissions – Grams per Piston Operation ...........................................123 Table 60 APA Pb Emissions – Percent by Mode ............................................................124 Table 61 APA Pb Emissions – CY2011 Operations (Tons) ............................................124 Table 62 SMO Pb Emissions – Grams per Piston Operation ..........................................126 Table 63 SMO Pb Emissions – Percent by Mode ............................................................127 Table 64 SMO Pb Emissions – CY2011 Operations (Tons) ...........................................128 Table 65 Sources for Meteorological Data .....................................................................131 Table 66 Modeling Parameters Common to All Airports ..............................................133 Table 67 RVS Site-Specific Modeling Parameters ........................................................134 Table 68 APA Site-Specific Modeling Parameters ........................................................135 Table 69 Site-Specific Modeling Parameters, SMO .......................................................136 Table 70 Airport-wide PM-Pb Emissions and Modeled Contributions at the North Monitor, RVS .............................................................................................................148 Table 71 Airport-wide PM-Pb Emissions and Modeled Contributions at the Central Monitor, APA ................................................................................................151 Table 72 Airport-wide PM-Pb Emissions and Modeled Contributions at the Northeast Monitor, SMO ...........................................................................................155 Table 73 Performance Measures for Comparing PM-Pb Model Predictions to Measurements ........................................................................................................157 -vii-

1. EXECUTIVE SUMMARY Lead (Pb) is a well-known air pollutant that can lead to a variety of adverse health impacts, including neurological effects in children that lead to behavioral problems, learning deficits, and lowered IQ. Concerns regarding the adverse health effects of exposure to airborne Pb resulted in its classification as an air pollutant pursuant to the Clean Air Act in 1976, followed by the requisite enactment of a health-based National Ambient Air Quality Standard (NAAQS) for Pb in 1978 (set at 1.5 micrograms per cubic meter based on quarterly average concentration). During the 1970s, the primary source of airborne Pb in the United States was the combustion of leaded gasoline in motor vehicles. Phase-out of leaded gasoline use in motor vehicles began in the mid-1970s with the introduction of catalytic converters, and the use was banned after December 31, 1995. The elimination of leaded gasoline use in motor vehicles left ore and metals processing, waste incinerators, utilities, lead-acid battery manufacturing, as well as the combustion of leaded aviation gasoline in piston- engine powered aircraft, as the major sources of airborne lead emissions. In October 2008, the U.S. Environmental Protection Agency (EPA) promulgated a new Pb NAAQS that lowered the acceptable level by an order of magnitude, to 0.15 micrograms per cubic meter based on a rolling three-month average concentration. In addition to promulgating the new Pb NAAQS, in December 2010 EPA revised requirements for ambient Pb monitoring around facilities known to have substantial Pb emissions. These facilities include airports with sufficient piston-powered aircraft activity that they are estimated to have annual Pb emissions of 1.0 ton or more. In addition, EPA is currently engaged in a monitoring study of 15 additional airports with estimated annual Pb emissions between 0.5 and 1.0 ton to investigate whether airports with this range of Pb emissions that meet additional criteria described by EPA that may have the potential to cause violations of the Pb NAAQS (U.S. EPA 2013). In light of the above, the Airport Cooperative Research Program (ACRP) initiated ACRP Project 02-34 entitled “Quantifying Aircraft Lead Emissions at Airports.” The first primary objective of this study is to review and improve upon existing methodologies to quantify and characterize aircraft-related Pb emissions at airports with significant populations of aircraft that use leaded aviation gasoline. The second primary objective is to create a guidance document that explains the refined methodology for quantifying airport Pb emissions such that it can be readily implemented by airports around the country seeking to assess the importance of aircraft-related Pb emissions at their facilities. This report focuses only on the first objective. -1-

Given the objective of reviewing and improving methods for quantifying aircraft-related lead emissions, the study involved the following five major phases: 1. A review of existing methodologies for quantifying aircraft-related Pb emissions; 2. Development of a refined methodology for estimating aircraft-related Pb emissions inventories that addresses shortcomings with existing methodologies identified during the critical review; 3. Conducting month-long field studies at each of three selected airports to gather site-specific data regarding aircraft activity, the lead content of aviation gasoline used at the airport, and data regarding ambient Pb concentrations, Pb particle size distributions, and Pb isotope ratios; 4. Application of the refined methodology to develop Pb emission inventories for three selected airports using both readily available activity data as well as the site- specific data; and 5. Validation of the refined methodology through comparison of dispersion modeling results based on the inventory computed using site-specific data with ambient Pb measurements made during the field study. During the course of the review of existing aircraft Pb quantification methodologies, issues and data gaps were identified in the following key areas: • Information regarding airframes and engines; • Engine fuel consumption rates and modal load assumptions; • Aviation gasoline lead concentrations; • Engine lead retention; • Aircraft time in mode; • Total aircraft operations, aircraft fleet operations, and temporal variations; • Contribution of non-combustion sources of lead; • Validation of emission estimates; and • Proper documentation of data and results. Based on the results of the critical review, a refined methodology for quantifying aircraft- related Pb emissions was developed and applied to estimate calendar year 2008 and 2011 aircraft-related Pb emissions. Emissions inventories resulting from engine exhaust were prepared using publicly available data for three selected airports with substantial piston- engine aircraft operations: Richard Lloyd Jones Jr. Airport (RVS) in Tulsa, OK; Centennial Airport (APA) in Denver, CO; and Santa Monica Municipal Airport (SMO) in Santa Monica, CA. The key differences between the refined methodology and the existing methodologies include the following: -2-

• Expansion of the number of aircraft and engine types considered; • Use of brake specific fuel consumption and engine load data by mode to estimate fuel consumption instead of volumetric fuel flow rates; • Use of the Federal Aviation Administration’s (FAA’s) Traffic Flow Management System Counts (TFMSC) database at https://aspm.faa.gov/TFMS/sys/ for the distribution of piston-powered aircraft operations; • Use of FAA’s Type Certificate Data Sheets (TCDS) to obtain engine characteristics data for piston-powered aircraft; • Use of FAA’s U.S. registration counts for the distribution of engines within a given piston-powered aircraft; and • Use of FAA’s General Aviation and Air Taxi Activity (GAATA) Survey defined at the regional level for the fraction of civilian operations of total piston-powered aircraft operations. In addition, the refined methodology was applied for calendar year 2011 at each airport using site-specific data gathered during the field studies regarding aircraft fleet characteristics, activity, and gasoline Pb content to estimate engine exhaust emissions. Annual Pb exhaust emissions as estimated using the refined methodology with publicly available data for 2008 are compared to the estimates obtained using existing methods in Table 1. The two results for Santa Monica Airport reflect differing assumptions regarding operational modes that were also used with the refined methodology. As shown, the differences in emission estimates for APA and RVS were relatively large and of opposite sign, while those for SMO were smaller. Also of note is that the refined methodology predicated higher emissions for two of the three airports. Annual Pb exhaust emissions as estimated using the refined methodology with publicly available data for 2011 are compared to the estimates obtained using the refined methodology with site-specific data in Table 2. Again, two results are shown for Santa Monica Airport based on the use of publicly available data reflecting the differing assumptions in operational modes discussed above, but both are compared to a single value obtained using the site-specific data gathered during the field study. As shown, use of the site-specific data resulted in lower estimated Pb emissions in all cases, with the differences being substantial in most cases. The site-specific data gathered during the field studies were also used to develop temporally and spatially resolved inventories for selected days on which ambient Pb concentrations were measured. These inventories were used as input to the AERMOD dispersion model to compute 12-hour average “modeled” concentrations that could be -3-

Table 1 Estimated Calendar Year 2008 Pb Emissions (tons per year) APA RVS SMO 1 SMO 2 Existing Methodologies 0.73 1.17 0.33 0.13 Refined Methodology 1.95 0.69 0.43 0.16 Note: The two results for Santa Monica Airport reflect differing assumptions regarding operational modes. Table 2 Estimated Calendar Year 2011 Pb Emissions (tons per year) APA RVS SMO 1 SMO 2 Refined Methodology – Publicly Available Data 1.76 0.48 0.38 0.14 Refined Methodology – Site-Specific Data 0.26 0.18 0.12 0.12 Note: The two results for Santa Monica Airport reflect differing assumptions regarding operational modes. compared to the monitored values in order to evaluate the performance of the refined methodology. These data are shown in Figure 1 for RVS, where the best agreement between modeled and monitored concentrations was observed. Data for APA, where the poorest agreement was observed are shown in Figure 2 and indicate an overprediction of ambient Pb levels. Finally, as shown in Figure 3, data for SMO indicated relatively good agreement except for two weekend days (shown as triangles) when the monitored concentrations were far higher than those modeled. Similar comparisons of modeled versus monitored concentrations made using the refined methodology but with publicly available data all showed poor agreement. Finally, the field study data also allowed assessment of the relative importance of resuspended lead (as opposed to Pb from only exhaust emissions) to total lead concentrations. Based on the comparisons of Pb concentrations in total suspended particulate (TSP) and fine particulate matter (PM2.5) measured at the three field study sites, what is believed to be resuspended lead in the coarse particle size range was observed to account for about 20–30% of the lead found in TSP. Furthermore, based on analysis of lead isotopes present in the samples collected at the field sites, the original source of the lead found in the coarse particle range appears to be the combustion of leaded aviation gasoline. -4-

Figure 1 Modeled versus Measured PM2.5-PbAt the RVS North Site Figure 2 Modeled versus Measured PM2.5-Pb at the APA Central Site -10 0 10 20 30 40 50 60 -10 0 10 20 30 40 50 60 M od el ed P b, n g/ m 3 Measured, Background-Corrected Pb, ng/m3 1 : 1 Line 0 10 20 30 40 50 60 0 10 20 30 40 50 60 M od el ed P b, n g/ m 3 Measured, Background-Corrected Pb, ng/m3 1 : 1 Line -5-

Figure 3 Modeled versus Measured PM2.5-Pb Concentrations at the SMO Northeast Site ### -10 0 10 20 30 40 50 60 70 -10 0 10 20 30 40 50 60 70 M od el ed P b, n g/ m 3 Measured, Background-Corrected Pb, ng/m3 1 : 1 Line -6-