SUPPLEMENTARY INFORMATION:

I. What is today's action?

This action announces the availability of two studies that contain information on ambient lead concentrations near an airport that has lead emissions from the combustion of leaded aviation fuel. The first is a local-scale airport modeling and monitoring study conducted by the EPA to investigate near-source ambient lead concentrations attributable to lead from the combustion of leaded aviation gasoline (EPA, 2010). The second is a final report documenting the study relied on in the proposed rule which was used to identify airports as having ( printed page 76337) the potential to exceed the lead NAAQS (South Coast Air Quality Management District, 2010). Both studies are located in Docket ID No. EPA-HQ-OAR-2006-0735.

II. How does this information relate to the Proposed Rule—revisions to lead ambient air monitoring requirements?

These two studies provide information on the potential for lead emissions from the combustion of leaded aviation fuel at airports to exceed the lead NAAQS as well as other information (locations of maximum emissions and lead concentration gradients) that may be referenced in the final rule.

The first study developed and evaluated an air quality modeling approach that could be used to evaluate local-scale concentrations of lead in the vicinity of an airport where piston-engine aircraft are operated. The study also included an assessment of the maximum 3-month average lead concentration and model sensitivity tests. The maximum 3-month average lead concentration was evaluated in order to compare the model output with the NAAQS for lead, 0.15 μg/m3, reported as the maximum 3-month average concentration.

Air monitoring was conducted to evaluate the performance of the air modeling approach, to assist in the quantification of the contribution of lead from general aviation emissions to local air quality, and to provide information about the change in lead concentrations with distance from the airport. Air quality modeling was conducted using EPA's American Meteorological Society/Environmental Protection Agency Regulatory Model or AERMOD. Inputs to the model included a comprehensive lead emission inventory incorporating on-site, time-in-mode and sub-daily activity data for piston engine aircraft. Model inputs also included considerations of aircraft-induced wake turbulence, plume rise of the aircraft exhaust, and allocation of approach and climb-out emissions to 50 meter increments in altitude.

To evaluate the modeling approach used here, ambient lead concentrations were measured upwind and downwind of the Santa Monica Airport and compared to modeled air concentrations. Modeling results paired in both time and space with monitoring data showed excellent overall agreement. Modeling results show aircraft engine run-up is the most important source contribution to the maximum lead concentration. Sensitivity analysis shows that engine run-up time, lead concentration in aviation gasoline, and the fraction of piston engine aircraft that are twin engine are the most important parameters in determining near-field lead 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 lead concentrations that exceed the current NAAQS for lead (0.15 μg/m³ ) and help inform the process for identifying locations of maximum concentration.

The second study is the final report on one of the airport studies referenced in the proposed rule. This report provides additional information on the approach, methods, and results of the study.

III. How can I get a copy of these documents and other related information?

1. Docket. EPA has established a docket for this action under Docket ID No. EPA-HQ-OAR-2006-0735. All documents in the docket are listed on the http://www.regulations.gov Web site. Although listed in the index, some information is not publicly available, e.g., Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copy form. Publicly available docket materials are available either electronically through http://www.regulations.gov or in hard copy at the Revisions to Lead Ambient Air Monitoring Requirements docket, Docket ID No. EPA-OAR-2006-0735, EPA Docket Center, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. This Docket Facility is open from 8:30 a.m. to 4:30 p.m. Monday through Friday excluding legal holidays. The docket telephone number is (202) 566-1742. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744.

2. Electronic Access. You may access this Federal Register document electronically through the EPA Internet under the “ Federal Register” listings at http://www.epa.gov/​fedrgstr/​.

IV. References

U.S. EPA (2010) Development and evaluation of an air quality modeling approach for lead emissions from piston-engine aircraft operating on leaded aviation gasoline. EPA-420-R-10-007. Available at http://www.epa.gov/​otaq/​aviation.htm.

South Coast Air Quality Management District (2010) General Aviation Airport Air Monitoring Study Final Report. Final Report.