Prepared by U.S. EPA Region III. Presented to the PDD Working Group August 24, 2004.:

U.S. EPA Disclaimer

EPA strongly cautions that these study results should not be used to draw conclusions about local exposure concentrations or risk. The results are most meaningful when viewed at the regional or county level; for smaller areas, the study becomes less certain. In addition, these results represent conditions in 1999 rather than current conditions and only include exposures from outdoor sources of particulate matter.

The results provide answers to questions about emissions, ambient air concentrations, exposures and risks across broad geographic areas for the year 1999. As such, they help the EPA identify specific air toxics compounds, and specific source sectors such as stationary sources or mobile sources, which generally produce the highest exposures and risks in the country. But they also are based on assumptions and methods that limit the range of questions that can be answered reliably. They cannot be used to identify exposures and risks for specific individuals, or even to identify exposures and risks in small geographic regions such as a specific neighborhood. These limitations, or caveats, must always be kept in mind when interpreting the results. The results should be used only to address questions for which the assessment methods are suited.

All risk estimates are based on exposure estimates for the median individual within each census tract, which EPA considers to be a "typical" exposure. Some individuals may have substantially higher or lower exposures based on where they spend their time. The study is not designed to quantify these individual extremes.


As part of the Philadelphia Air Toxics Project, EPA Region III and EPA Office of Air Quality Planning and Standards evaluated the economic impact of diesel particulate matter in the 5 county Philadelphia metropolitan area. This is the first-ever regional study to put a dollar value on diesel particulate matter (PM).

EPA developed economic analysis software for fine PM. Philadelphia is the first test case of the local-scale version of the software. It works by matching changes in particulate matter with known health effects and an economic analysis. EPA uses similar methodology for valuating the cost and benefits of environmental regulations, including the Clean Air Act from 1990 to 2010, Clear Skies and the Non-Road Diesel Rule.

Here are some key points of the study:

  • The Diesel Difference: The model assumed all on-road and non-road diesel emissions were zero.
  • Inputs: Modeled data from 1999 NATA study.
  • Health impacts based on peer-reviewed epidemiological studies.
  • Costs were calculated using willingness to pay, cost of illness, and lost wages in year 2000 dollars.
  • Study area: Counties of Philadelphia, Bucks, Montgomery, Chester, and Delaware County.

Here are some of the findings for the 5 county area:

In 1999 Diesel PM caused:

  • 260 deaths at a cost of $1.4 billion.
  • 450 Non-fatal heart attacks at a cost of $37 million.
  • 32,000 missed days of work at a cost of $4.4 million in wages.
  • 3,700 Asthma attacks at a cost of $160,000.
  • 300 Respiratory and cardiovascular hospital admissions at a cost of $4.7 million.

How Was The Analysis Done?

There is a large body of science that ties fine PM with shortened life spans, heart attacks, asthma attacks, missed work days and other health end points. Further, there is strong economic analysis of each health end point. Therefore, knowing the diesel PM concentration in Philadelphia, we calculated health impacts and put a dollar value on those impacts. There were three components of the analysis:

1) Modeled change in particulate matter concentration
2) Health impacts assessment
3) Economic analysis.

Modeling the Diesel Difference

There are many sources of particulate matter, including diesel trucks and buses, construction equipment, secondary formation from VOCs, and natural background sources. This study investigated the diesel on-road and non-road contribution to PM. The costs of diesel PM were calculated by subtracting the diesel PM contribution from the overall PM concentration - the diesel difference.

The project used point and area source emissions inventory data prepared for the 1999 National Air Toxics Assessment (NATA) study, with some updates provided by State/local agencies. Mobile source emissions have been separately calculated and assigned to highways. The project used the ISC model to estimate air toxics concentrations resulting from primary air toxics emissions, and the CMAQ model to estimate air toxics emissions from secondary formation.

Health Impacts

Health impact calculations were derived from the epidemiological literature. EPA relied on effect estimates from published, peer-reviewed studies that relate health effects to ambient concentrations of PM. While a broad range of serious health effects have been associated with exposure to elevated PM, EPA included only a subset of health effects due to limitations in available effect estimates and concerns with double counting of overlapping effects. None of the effects are double counted.

The premature mortality estimate was based on a prospective cohort long-term exposure study. EPA selected an effect estimate from the extended analysis on the American Cancer Society cohort (Pope et al., 2002) because it represents the most comprehensive cohort analysis with the longest period of follow-up. The effect estimate quantifies the relationship between annual mean PM 2.5 levels and all-cause mortality in adults 30 and older.

Economic Analysis

The standard approach to placing a dollar value on the life-saving benefits of regulations is based on societal willingness to pay (WTP) for risk reductions. Unlike an emergency rescue operation, the specific people whose lives are saved by regulations cannot be identified. Instead, regulations reduce mortality risks in the population affected by the regulation.

Based on an extensive review of the research literature, the U.S. EPA estimated the value of statistical life (VSL) with a mean of $5.5 million with a confidence interval of plus or minus $2.3 million (in 2000 dollars). EPA's review identified studies that were judged to reflect sound and defensible methods. Some of the studies used the contingent valuation method, where survey respondents are directly asked about their WTP for mortality risk reductions. Other studies estimated the value of risk reductions based on workers' willingness to accept riskier jobs in return for higher wages. The conceptual foundation of both empirical approaches to estimating the VSL is that societal WTP for risk reductions should reflect individuals' risk valuations, whether elicited directly through surveys or revealed in their labor market decisions.

Asthma attacks were similarly valuated using the willingness to pay approach. Asthma attacks are valued at $42 per incidence, based on the average WTP estimates. The valuation was based on a study that surveyed asthmatics to estimate WTP for avoidance of a 'bad asthma day', as defined by the subjects.

Non-fatal heart attack costs were calculated as the cost of illness (COI). It was estimated using age specific COI values reflecting lost earnings and direct medical costs over a 5-year period following a non-fatal heart attack, with a 3 percent discount rate. The age specific COI values are as follows:



66 and over



Hospital admissions costs are COI estimates based chronic obstructive pulmonary disease (COPD) and cardiovascular admissions. The costs reflect average hospital care costs, average length of hospital stay, and lost earnings. The average cost for COPD is $12,378 and the cost for cardiovascular admissions is $18,387.

The cost of work loss days is based on county-specific median annual wages divided by 50 weeks (assuming 2 weeks of vacation), then by 5 to get median daily wage. The source of the wages was the 2000 Census. The median daily wage by county is as follows: Bucks $157; Chester $172, Delaware $152; Montgomery $168, Philadelphia $125.

Results By County

Below are county estimates for pre-mature mortality, non-fatal heart attacks, asthma attacks, missed work days and hospital admissions. The hospital admissions results are for cardiopulmonary and respiratory admissions. To ensure no double counting, hospital admissions do not include asthma emergency room visits and non-fatal heart attacks. The asthma attacks values do not include asthma attacks that require emergency room visits.

All results are reported to two significant figures. Due to rounding, the results by county may not add-up to the 5 county area results presented on the first page.







$94 million
$50 million
$170 million
$130 million
$990 million




$3.1 million
$1.8 million
$4.8 million
$4.6 million
$23 million



















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