EPA420-R-99-013
                                                 April 1999
                                                           
                              
                              
                        Final Report
                              
                              
           Evaluation of Air Pollutant Emissions
           from Subsonic Commercial Jet Aircraft
                              
                              
          Engine Programs and Compliance Division
                  Office of Mobile Sources
            U.S. Environmental Protection Agency
                 Ann Arbor, Michigan 48105
                              
                              
                    Prepared for EPA by
                    ICF Consulting Group
                EPA Contract No. 68-C-98-170
                  Work Assignment No. 0-3
                              

                              
                     EXECUTIVE SUMMARY

The U.S. Environmental Protection Agency's (EPA's) Office of
Mobile Sources initiated this study in order to assess the
existing and potential impact of aircraft emissions on local air
quality at ten selected cities.  Aircraft emissions and airport
related emissions have received considerable attention in recent
years, both on national and international agendas.  

Recent activities, such as the Clean Airport Summit (held in
Denver December 1997), a National Resources Defense Council
(NRDC) report, and correspondence from state and local air
quality agencies, reflect increased awareness of ground-level
aircraft emissions. State and local air quality officials are
seeking strategies for cost-effective emissions reductions to
comply with National Ambient Air Quality Standards.  Perhaps most
significant on the national agenda, EPA and Federal Aviation
Administration (FAA) have convened a multi-stakeholder process to
seek a voluntary agreement on ground-level emissions reductions
actions for commercial aircraft and aviation-related emissions.
In order to focus the analysis, EPA made the following decisions
regarding the scope of this study:

 * Estimate the emissions from commercial jet aircraft only
   (exclude emissions from on board auxiliary power units) 

 * Select ten cities with current or potential local air quality
   problems, as indicated by compliance with the ozone National
   Ambient Air Quality Standards

 * Rely on the methodology presented in EPA Procedures for
   Emission Inventory Preparation, Volume 4 : Mobile Sources,
   dated 1992

 * Seek data sources that are national in scope and readily
   available 

 * Use 1990 as a base year, and 2010 as the projection year due
   to availability of total regional emission data for these
   years, and the desire to identify potential long-term trends
   in emissions growth.

In the study, one portion of the airport-related emissions,
commercial aircraft, were projected to the year 2010.  After an
initial draft of the study was prepared, EPA invited comments on
the draft report from the multi-stakeholder group.  The most
significant comments are included in text boxes throughout the
report. 

The analytical results of the study confirm that commercial
aircraft emissions have the potential to significantly contribute
to air pollution in the ten study areas.  Study results indicate
that in 1990, for NOx, the aircraft component of the regional
mobile source emissions ranged from 0.6% to 3.6%.  In the 2010
projection year for all cities studied, the projected
ground-level emissions from commercial aircraft increased in
absolute terms.  The proportion of total urban emissions
attributable to aircraft also increased for all ten cities (range
from 1.9% to 10.4% of the regional mobile source NOx emissions);
these proportions were calculated using aircraft emissions
calculated in this study and total emissions from 1990 and 2010
inventories previously developed by EPA.  While there is
uncertainty associated with these estimates for the projection
year, they generally suggest an increase in ground-level
emissions from commercial aircraft as a result of forecast growth
in the aviation sector. 

Comments received from reviewers of the draft study indicated
that uncertainty may exist in the national forecasts of growth in
aircraft activity, on future composition of the aircraft fleet,
and on the accuracy of a default mixing height.  Such
uncertainties carry over into projections of future emissions,
and resolution of uncertainties may result in higher or lower
ground-level emissions estimates from future aircraft.  In order
to reduce the uncertainty of the results presented, additional
areas for investigation would be 

 * Improvements in activity forecasts to account for supply-side
   constraints that could dampen growth rates (e.g.,
   infrastructure limitations, funding limitations, limited gate
   availability, regulatory constraints)

 * Improvements in forecasts of national level fleet turnover

 * Addition of sensitivity analyses for the above key parameters
   and others such as mixing height

Thus, this study has achieved its initial goals and creates a
basic understanding of ground-level aircraft emissions
contribution.  It provides an estimation of the contribution of
aircraft to air quality emissions in ten urban areas, confirms
that investigation of cost-effective control options on aircraft
emissions is warranted, and highlights the need for improvements
in the quality of national level data as noted by reviewers of
the draft study if more certainty is desired.  Reliance upon the
study's conclusions should take into account the caveats noted in
this report.