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Premature Mortality Due to Particulate Air Pollution in 239 American Cities

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In late April 1996, after Breath-taking went to press, the U.S. Environmental Protection Agency released two publications containing significant new information relevant to the findings of NRDC's report. These are:

  • a revised External Review Draft of the EPA Staff Paper "Review of the National Ambient Air Quality Standards on Particulate Matter," and
  • a final Criteria Document entitled "Air Quality Criteria for Particulate Matter."

The April External Review Draft Staff Paper contains new recommendations for the EPA Administrator regarding proposed health standards for fine particles (PM2.5) and potential changes to the existing standards for PM10. It also contains city-specific assessments of mortality attributable to particulate air pollution for portions of Philadelphia and Los Angeles. The April Criteria Document contains new data on the ratio between PM2.5 and PM10 for Philadelphia and a number of cities in California.

This addendum outlines the new information contained in these EPA reports and explains their significance to Breath-taking . In sum, we found that:

    A. New proposed levels indicate that the EPA is moving toward tightening particulate standards. Despite this positive trend, the new standards still do not go far enough in protecting public health.

    B. The EPA's new mortality estimates for portions of Philadelphia and Los Angeles are consistent with the numbers reported by NRDC for these Metropolitan Statistical Areas and confirm the methodology used in Breath-taking.

    C. New information on the ratio between PM2.5 and PM10 in specific cities bears out mortality estimates reported in Breath-taking . Monitoring data that documents this ratio for specific cities is very sparse, and NRDC therefore relied on the generally accepted assumption that this ratio in U.S. cities is approximately 60 percent.

A. Analysis of Alternative Standard Levels

Breath-taking presents a discussion and analysis of alternative levels for health standards under consideration by the EPA. It is based upon the recommendations contained in an earlier (November 1995) version of the Draft EPA Staff Paper entitled "Review of the National Ambient Air Quality Standards on Particulate Matter."

Several Sections of Breath-taking refer directly to the November 1995 draft, including page 2 in the Executive Summary, pages 86-89 in Chapter 3, and pages 127-130 in Chapter 6.

The EPA's new recommendations contained in the April draft suggest that the EPA Administrator should consider the following:

    a.) Establishing a new annual average standard for PM2.5 in the range of 12.5-20 micrograms per cubic meter (µg/m3); and

    b.) Establishing a new 24-hour standard for PM2.5 in the range of 18-65 µg/m3.

These ranges for the annual average and 24-hour standards for PM2.5 are lower at both the upper and lower ends than the ranges suggested in the November 1995 Draft Staff Paper, which had recommended a range of 15-30 µg/m3 for the annual average standard, and a range of 25-85 µg/m3 for the 24-hour standard.

The lower ranges for fine particle standards in the April 1996 Staff Paper represent considerable movement in the right direction.

With respect to PM10, the April 1996 External Review Draft Staff Paper suggests that the EPA Administrator consider:

    a.) Retaining an annual average PM10 standard in the range of 40-50 µg/m3 (the current standard is 50 µg/m3) alone, or in conjunction with a 24 hour PM10 standard; and

    b.)Consider retaining the 24-hour PM10 standard of 150 µg/m3 while allowing for multiple exceedances.

The April 1996 version of the Staff Paper suggests a slight strengthening of the annual average standard for PM10 and a slight relaxation of the 24-hour standard (with the provision for multiple exceedances), if that standard is retained. The November 1995 Draft Staff Paper had suggested retaining the annual average PM10 standard at the current level and dropping the 24-hour standard.

Breath-taking analyzed the impact of alternative levels of an annual average standard for PM2.5. The table below incorporates the benefits of the new standard ranges now being considered by the EPA.

Revised Table 18: Number of Lives Prolonged by Fine Particle Standard

PM2.5 Annual Standard Level (µg/m3) Description Estimate of Cardiopulmonary Deaths Prevented
Point Estimate, (Range)
10 NRDC Recommended Level 56,238 (33,570-76,874)
12.5 New Lower End of EPA Range 37,562 (22,599-50,957)
15 Former Lower End of EPA Range 21,676 (13,160-29,151)
20 New Upper End of EPA Range 4,662 (2,895-6,134)
30 Former Upper End of EPA Range 108 (70-137)

The table indicates that if the EPA set standards at the lower end of the recommended range, an estimated 37,562 lives would be prolonged annually, with 4,662 lives prolonged at the upper end of the range. This compares to the prior range of 15-30 µg/m3, where the estimates of lives prolonged cited in Breath-taking ranged from 21,676-108.

B. EPA Estimates of Premature Mortality

New information concerning two specific cities is also found in the April 1996 External Review Draft of the EPA Staff Paper "Review of the National Ambient Air Quality Standards for Particulate Matter." The Staff Paper contains a city-specific risk assessment for the City of Philadelphia and for portions of Los Angels County, and reports on PM10 and PM2.5 monitoring values for Los Angeles and Philadelphia. The data presented in Table VI-1 of the EPA Staff Paper indicate that the ratio of PM2.5 to PM10 for Los Angeles is 58 percent and for Philadelphia is 69 percent.

There are a number of important differences in approach between the NRDC and the EPA analyses. For instance, there are differences in the monitoring stations used and the years for which monitoring data were analyzed. However, the most significant factor, which dominates the differences in the reported results, is that the NRDC analysis and the EPA analysis cover different geographic areas.

The NRDC report considers the entire Metropolitan Statistical Area. In the case of Philadelphia, this includes eight counties: Burlington County, New Jersey; Camden County, New Jersey; Gloucester County, New Jersey; Bucks County, Pennsylvania; Chester County, Pennsylvania; Delaware County, Pennsylvania; Montgomery County, Pennsylvania; and Philadelphia County, Pennsylvania. The EPA analysis considers only Philadelphia County. The area covered by the EPA Philadelphia analysis includes one-third the population of the entire MSA, and the estimate of premature deaths is one-third of that reported by NRDC (920 deaths compared to 2,599). Similarly for Los Angeles, the NRDC analysis covers LA County in its entirety, while the EPA analysis deals only with the southeast portion of the county, including central Los Angeles, Pasadena, and Lynwood. The population of the area covered in the EPA analysis is about half of the total county population, and the estimate of attributable deaths is 37 percent of that estimated by NRDC -- 2,190 compared to 5,873.

The EPA Risk Assessment also reports estimates of air pollution-induced mortality associated with short-term exposures, of hospital admissions for respiratory and cardiac causes, and of number of cases of lower respiratory symptoms, shortness of breath, and acute bronchitis in children.

The similarity of the EPA's new findings to the numbers reported in Breath-taking bears out the appropriateness of NRDC's methodology.

C. City-Specific Monitoring Data on PM2.5/PM10 Ratio

The analysis of premature mortality in Breath-taking relies on the standard assumption that the average PM2.5/PM10 ratio in urban areas in the U.S. is approximately 60 percent. This is the conversion factor used by Dockery and Pope in their 1994 meta-analysis. The 60 percent factor represents a reasonable assumption for national analysis.

City-specific PM2.5 monitoring stations are very few in number, with most monitoring stations located in remote areas. Only a few urban areas report PM2.5 concentrations to the EPA's national AIRS database. In contrast, there are more than 900 PM10 monitors in urban areas.

The final EPA Criteria Document contains new data on PM 2.5/PM10 ratios provided by the California Air Resources Board (CARB) to the EPA for eight monitoring stations in California, six of which are in urban areas. Information is also included for a site in Philadelphia. The annual average ratios reported by CARB for the California urban sites were all 50 percent or lower. The mean ratio reported for Philadelphia was 71 percent.

NRDC calculated mortality estimates using the city-specific PM2.5/PM10 ratios provided in the Criteria Document Table 6-16 for Philadelphia, Visalia, San José, Riverside, Stockton, and Bakersfield. In addition, we calculated the estimates for Los Angeles, using the ratio reported in the April 1996 Staff Paper. We also calculated values for three California areas for which there is no local city-specific data but which are near localities included in the CARB data: San Francisco (using the value for nearby San San José); Sacramento (using the value for Stockton); and Fresno (using the Visalia value).

Tables A-1 and A-2 present the results of the calculations.

Table A-1
Alternate Calculations Using City-Specific PM2.5/PM10 Ratios

Metropolitan Statistical Area PM2.5/PM10 Ratio Original Estimate of Cardiopulmonary Deaths Attributable to Particulate Air Pollution Alternate Estimate of Cardiopulmonary Deaths Attributable to Particulate Air Pollution Original Estimate of Attributable Deaths Per 100,000 Population Alternate Estimate of Attributable Deaths Per 100,000 Population
Riverside-San Bernardino 0.49 1,905 (1,158-2,560) 1,437 122 92
San José 0.49 447 (266-612) 301 39 23
Stockton 0.46 321 (194-433) 215 93 62
Bakersfield 0.44 464 (284-618) 308 115 76
Visalia-Tulare-Porterville 0.49 302 (186-402) 259 123 105
Los Angeles 0.58 5,873 (3,550-7,933) 5,594 79 75
Philadelphia 0.71 2,599 (1,550-3,556) 3,388 55 72

Table A-2
Alternate Calculations Using PM2.5/PM10 Ratios for Nearby Cities

(City-Specific Ratios Not Available)

Metropolitan Statistical Area PM2.5/PM10 Ratio Original Estimate of Cardiopulmonary Deaths Attributable to Particulate Air Pollution Alternate Estimate of Cardiopulmonary Deaths Attributable to Particulate Air Pollution Original Estimate of Attributable Deaths per 100,000 Population Alternate Estimate of Attributable Deaths Per 100,000 Population
Fresno 0.49 488 (298-653) 373 95 72
Sacramento 0.46 488 (290-669) 280 48 28
San Francisco-Oakland 0.49 1,270 (752-1,748) 797 39 25

For 9 of 10 MSAs, the alternate estimates fall within the ranges reported in NRDC's Base Case analysis using the national default assumptions, indicating that the methodology used in the NRDC Base Case was reasonable. The one exception is Sacramento, a city for which a city-specific ratio was not available.

The calculations using the city-specific ratios do not significantly change the rankings on the number of attributable deaths reported in Breath-taking to provide relative comparisons among cities. The alternate estimates do not affect the rankings for top-ranked Los Angeles, Philadelphia or Riverside. San Francisco, however, would drop from 7 to 19. Fresno, Bakersfield, and San José would drop down in ranking, but would still fall within the 50 MSAs nationwide. Sacramento, Stockton, and Visalia-Tulare-Porterville would drop off the top 50 list.

Rankings for attributable deaths per 100,000 population also would change slightly based on the CARB data. The ranking of Visalia and Riverside as number one and number two in terms of attributable death rate relative to other cities remain the same, and Bakersfield moves from 3 to 4. Sacramento would drop off the top 50 list.

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