Quantifying Aircraft Lead Emissions at Airports (2015) / Chapter Skim
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From page 131... ...
7. AIR QUALITY MODELING AND EMISSION INVENTORY EVALUATION 7.1 Air Quality Modeling Using the spatially and temporally resolved Pb emissions estimates described in Chapter 6, an ambient air quality modeling assessment was performed for each study site to evaluate how well modeled and measured localized ground-level lead concentrations compare at the sampling locations for each of the three airports.
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7.1.1 Model Options The model has a set of recommended default options for the user for some of these parameters. AERMOD was typically run using the following options: • U.S.
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The values for the surface characteristics of albedo, Bowen ratio, and surface roughness appropriate to the area around the surface meteorological monitoring stations were obtained from AERSURFACE. AERSURFACE is a surface-characteristic preprocessor that is part of the AERMOD modeling system.
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Table 66 Modeling Parameters Common to All Airports Activity Parameter Value Reference Fixed-wing Aircraft Taxi Source separation distance 18.29 meters Based on CALINE assumptions Takeoff Source separation distance 50 meters Based on ICF report Climb-out_1 Initial portion of climb-out 50 feet Based on performance statistics from aircraft owner's manuals1 Landing Source separation distance 50 meters Based on ICF report Approach Vertical extent of modeling domain Traffic pattern altitude Traffic pattern altitude – same as lead inventory Run-up Source separation distance 100 feet Based on ICF report Width of volume source 100 feet Assumed size of area in which run-up takes place Touch and go Source separation distance 50 meters Based on ICF report Helicopters Climb-out Angle of climb 3.7 degrees Variable – aircraft approach angle used Vertical extent of modeling domain 500 feet Traffic pattern altitude – same as lead inventory Approach Vertical extent of modeling domain 500 feet Traffic pattern altitude – same as lead inventory 1 See Section 6.1.4 for a discussion of the development of these performance characteristics and modeling parameters.
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From page 135... ...
Table 67 RVS Site-Specific Modeling Parameters Activity Parameter Value Reference Fixed-wing Aircraft Taxi Width of taxiway 40 feet Taken from airport diagrams Takeoff Width of runway 50 or 100 feet Taken from airport diagrams Location where aircraft leaves runway 1,145 feet from start of runway Based on observations of aircraft activity Climb-out_1 Angle of climb 4.9 degrees Based on performance statistics from aircraft owner's manuals1 Climb-out_2 Angle of climb 4.9 degrees Based on performance statistics from aircraft owner's manuals1 Remainder of climb-out 50 feet to 1,075 feet Traffic pattern altitude – same as lead inventory Landing Width of runway 50 or 100 feet Taken from airport diagrams Location where aircraft touches down 890 feet from start of runway Based on observations of aircraft activity Approach Glide slope angle 3.7 degrees Based on performance statistics from aircraft owner's manuals1 Vertical extent of modeling domain 1,075 feet Traffic pattern altitude – same as lead inventory Touch and go Width of runway 100 feet Take from airport diagrams Location where aircraft leaves runway 768 feet from start of runway Based on observations of aircraft activity Location where aircraft touches down 2,161 feet from start of runway Based on observations of aircraft activity Helicopters Approach Angle of descent 3.7 degrees Variable – aircraft approach angle used 1 See Section 6.1.4 for a discussion of the development of these performance characteristics and modeling parameters.
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From page 136... ...
Table 68 APA Site-Specific Modeling Parameters Activity Parameter Value Reference Fixed-wing Aircraft Taxi Width of taxiway 40 feet for minor taxiways; 50 ft for major taxiways. For modeling, 40 feet use uniformly assumed Taken from airport diagrams Takeoff Width of runway 75, 80 and 100 feet Taken from airport diagrams Location where aircraft leaves runway Distance from start of runway Based on observations of aircraft activity 2,785 ft 35L, 35R@A18, 17R, 10, 28@C5 4,299 ft 35R @A16 5,795 ft 35R @A14 1,145 ft 17L 4,173 ft 28@C4 Climb-out_1 Angle of climb 3.4 degrees Based on performance statistics from aircraft owner's manuals1 Climb-out_2 Angle of climb 4.9 degrees Based on performance statistics from aircraft owner's manuals1 Remainder of climb-out 50 feet to 1,000 feet Traffic pattern altitude – same as lead inventory.
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Table 69 Site-Specific Modeling Parameters, SMO Activity Parameter Value Reference Fixed-wing Aircraft Taxi Width of taxiway 40 feet Taken from airport diagrams Takeoff Width of runway 145 feet Taken from airport diagrams Location where aircraft leaves runway 1,145 feet from start of runway Based on observations of aircraft activity Climb-out_1 Angle of climb 4.9 degrees Based on performance statistics from aircraft owner's manuals1 Climb-out_2 Angle of climb 4.9 degrees Based on performance statistics from aircraft owner's manuals1 Remainder of climb-out 50 feet to 1,212 feet Traffic pattern altitude – same as lead inventory Landing Width of runway 145 feet Taken from airport diagrams Location where aircraft touches down 1,200 feet from start of runway Based on observations of aircraft activity Approach Glide slope angle 3.7 degrees Based on performance statistics from aircraft owner's manuals1 Vertical extent of modeling domain 1,212 feet Traffic pattern altitude – same as lead inventory Touch and go Width of runway 145 feet Taken from airport diagrams Location where aircraft leaves runway 930 feet from start of runway Based on observations of aircraft activity Location where aircraft touches down 1,600 feet from start of runway Based on observations of aircraft activity Helicopters Approach Angle of descent 3.7 degrees Variable – corkscrew approach used 1 See Section 6.1.4 for a discussion of the development of these performance characteristics and modeling parameters.
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Consistent with modeling performed previously at SMO, a source spacing of 50 meters was used for the runway. This distance balances the computational requirements with sufficient source density to preserve the horizontal geometry of the source configuration and accurately simulate the near-field concentration gradient.
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• Approach/landing – The period of operation between the time the aircraft elevation is below the traffic pattern altitude (as defined for climb-out) until the aircraft touches down on the runway.
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sources representing fixed-wing aircraft was calculated as the sum of three components: wingspan wake, horizontal momentum, and propeller turbulence wake. The values for these components were taken from the ICF report.
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Figure 38 RVS Receptor Grid -140-
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Figure 39 APA Receptor Grid -141-
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Figure 40 SMO Receptor Grid -142-
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7.1.5 Spatial Extent of Modeled PM-Pb Impacts Hourly airborne PM-Pb concentration fields for each of the three airports were modeled using site-specific aircraft activity data. The modeled hourly concentrations were used to generate average impacts for the PM sampling field studies.
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Figure 42 shows the modeled period-average PM-Pb concentrations at APA. The zone of Pb impacts -- operationally defined as concentrations exceeding the 75th percentile measured PM2.5-Pb background concentration of 2 ng/m3 -- is again generally confined to within the airport footprint.
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Figure 43 Modeled Period-Average PM-Pb Concentrations at SMO Note: Airport property boundaries are designated by a thick black line; dark interior lines indicate runways. 7.2 Comparison of Modeled and Monitored PM-Pb Concentrations This section compares the results of the air quality modeling using PM-Pb emission estimates based on site-specific data to the results of the on-site ambient monitoring to evaluate the performance of the refined aircraft operations PM-Pb emissions estimation methodology.
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• Takeoff, • Climb-Out, • Approach, • Landing, • Touch and Go, • Hangars, and • Helicopters. The source groups were similar to those defined in the emission inventory (Chapter 6)
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Figure 44 Modeled versus Measured PM2.5-Pb at the RVS North Site Table 70 shows the source group contributions to airport-wide PM-Pb emissions and to modeled concentrations at the North monitor. Taxiways, takeoffs, and runup activities were the largest contributors to the modeled period-average PM-Pb concentration at the North sampling location.
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Table 70 Airport-wide PM-Pb Emissions and Modeled Contributions at the North Monitor, RVS Source Group Percentage of Total Emissions (%) Period-Average Contribution at North Monitor (%)
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Figure 45 Modeled Total and Source-Group-Specific PM-Pb Concentrations at RVS Note: Airport property boundaries are designated by a thick black line; dark interior lines indicate runways. 7.2.2 APA – Centennial Figure 46 compares the modeled results from APA based on site-specific data to background-corrected measured concentrations for the primary downwind monitor.
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Figure 46 Modeled versus Measured PM2.5-Pb at the APA Central Site contrast to RVS, there is a bias at APA with the modeled concentrations persistently higher than the measured concentrations. For modeled concentrations above 20 ng/m3, the modeled and measured values are well correlated.
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Measured and modeled concentrations were typically low at the remaining three sampling locations. Two out of the six samples with excess PM-Pb had measured values within a factor of two of the modeled values.
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Days with the largest differences between modeled and measured concentrations generally corresponded to above-average modeled contributions from runup sources. This suggests runup contributions may be overestimated at the Central monitor.
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Figure 47 Modeled Total and Source-Group-Specific PM-Pb Concentrations at APA Note: Airport property boundaries are designated by a thick black line; dark interior lines indicate runways.
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Figure 48 Modeled versus Measured PM2.5-Pb Concentrations at the SMO Northeast Site Modeled airport-wide total emissions contributions of the different source groups to modeled concentrations at the Northeast site are shown in Table 72. Runup, taxiways, and takeoffs collectively contributed about 90% of the modeled impacts at the Northeast monitor while accounting for only about 35% of the total emissions.
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Table 72 Airport-wide PM-Pb Emissions and Modeled Contributions at the Northeast Monitor, SMO Source Group Percentage of Total Emissions Period-Average Contribution at Northeast Monitor (%) Range of Contributions at Northeast Monitor (%)
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Figure 49 Modeled Total and Source-Group-Specific PM-Pb Concentrations at SMO Note: Airport property boundaries are designated by a thick black line; dark interior lines indicate runways. 7.2.4 PM2.5-Pb Model Prediction to Measurement Summary Modeled and measured 12-hour average PM2.5-Pb concentrations for the downwind primary sites at each airport were presented as scattergrams in the previous section.
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emissions. Second, the two SMO samples with measured values far exceeding the modeled values (triangles in Figure 48)
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Based on the ratio of means, the model is 11% high at RVS and 11% low at SMO, while the model is 76% high at APA. The normalized mean square error (NMSE)
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In summary, the refined emission inventory methodology with site-specific data consistently outperformed the refined emission inventory methodology with publicly available data when using dispersion modeling to compare to measured PM-Pb concentrations. Aircraft operations occur over large footprints and thus it is necessary to accurately specify the timing and especially the location of emissions to accurately predict airborne PM-Pb concentrations.
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