Dispersion Modeling of Lead Emissions from Piston Engine Aircraft at General Aviation Facilities

In 2008, the national ambient air quality standard (NAAQS) for lead was tightened by an order of magnitude. General aviation is now the largest source of lead emitted to the atmosphere. The accuracy of modeled lead impacts from general aviation airports is unclear because of uncertainties in both emissions estimation and dispersion modeling. Aviation industry and environmental policy makers must understand how well such modeling can perform when data on aircraft activities at an airport are limited. To estimate the lead impacts at an airport with lead monitoring, this study used aggregate activity information and simple assumptions about the nature of activities; the goal was to evaluate the level of accuracy that could be achieved in the collection of data on lead emissions. Dispersion modeling of general aviation lead emissions was performed for Centennial Airport, Englewood, Colorado, to estimate near-field impacts from airport operations in 2011. Emissions were estimated with the use of FAA's Air Traffic Activity System and Emissions and Dispersion Modeling System. The annual emission estimate for 2011 was 0.43 ton, much lower than the 0.73 ton estimated by the 2008 National Emissions Inventory. Sensitivity analyses were conducted by varying several emission parameters. Modeled concentrations at the on-Site lead sampler were quite sensitive to the amount of run-up emissions. Concentrations modeled with Automated Surface Observing System meteorology have greater correlation with on-site measured values than those modeled with integrated surface hourly meteorology. Three-month average impacts modeled at the on-site lead-sampling location ranged from 10 to 20 ng/m(3), well below the lead NAAQS of 150 ng/m(3).