Development and evaluation of an air quality modeling approach to assess near-field impacts of lead emissions from piston-engine aircraft operating on leaded aviation gasoline

Abstract

Abstract Since aviation gasoline is now the largest remaining source of lead (Pb) emissions to the air in the United States, there is increased interest by regulatory agencies and the public in assessing the impacts on residents living in close proximity to these sources. An air quality modeling approach using U.S. Environmental Protection Agency’s (EPA) American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) was developed and evaluated for estimating atmospheric concentrations of Pb at and near general aviation airports where leaded aviation gasoline (avgas) is used. These detailed procedures were made to accurately characterize emissions and dispersion leading to improved model performance for a pollutant with concentrations that vary rapidly across short distances. The new aspects of this work included a comprehensive Pb emission inventory that incorporated sub-daily time-in-mode (TIM) activity data for piston-engine aircraft, aircraft-induced wake turbulence, plume rise of the aircraft exhaust, and allocation of approach and climb-out emissions to 50-m increments in altitude. To evaluate the modeling approach used here, ambient Pb concentrations were measured upwind and downwind of the Santa Monica Airport (SMO) and compared to modeled air concentrations. Modeling results paired in both time and space with monitoring data showed excellent overall agreement (absolute fractional bias of 0.29 winter, 0.07 summer). The modeling results on individual days show Pb concentration gradients above the urban background concentration of 10 ng m−3 extending downwind up to 900 m from the airport, with a crosswind extent of 400 m. Three-month average modeled concentrations above the background were found to extend to a maximum distance of approximately 450 m beyond the airport property in summer and fall. Modeling results show aircraft engine “run-up” is the most important source contribution to the maximum Pb concentration. Sensitivity analysis shows that engine run-up time, Pb concentration in avgas, and the fraction of piston-engine aircraft that are twin-engine are the most important parameters in determining near-field Pb concentrations. Year-long air quality modeling for 2008 and sensitivity analysis for the maximum 3-month average concentration period suggest the potential for 3-month average Pb concentrations that exceed the current National Ambient Air Quality Standard for Lead (0.15 μg m−3). The modeling methodology used in this analysis is generally transferable to other general aviation single runway airports in coastal environments of which there are over 1700 in the United States. This modeling approach can also be used to evaluate the air quality improvements from various emission reduction measures.