Click here to view the complete article as an Adobe Acrobat PDF.

Introduction

In Digging Up Trouble: The Health Risks of Construction Pollution in California, the Union of Concerned Scientists (UCS) claims air pollution from construction vehicles is killing more than 1,100 Californians each year, sending similar numbers to the hospital, and sickening hundreds of thousands more.[1] UCS estimates the economic toll at more than $9 billion per year. Fortunately, these claims have little to do with reality. UCS exaggerates harm from air pollution by excluding contrary evidence and ignoring weaknesses in studies that support its predetermined conclusions.

Visiting Scholar Joel Schwartz

According to UCS, the harm from construction emissions results mainly from two air pollutants: particulate matter (PM) and ozone. PM can be directly emitted (e.g., diesel smoke) or formed in the atmosphere from gaseous emissions (e.g., nitrogen oxides (NOx) can be converted to particulate nitrate). The California Air Resources Board (CARB) estimates that construction equipment contributes 3 percent of statewide direct fine particulate matter (PM2.5) emissions and 28 percent of PM2.5 emissions from diesel vehicles specifically.[2] Ozone is not directly emitted, but is formed in the atmosphere through reactions of NOx and volatile organic compounds (VOC) in the presence of sunlight. CARB estimates that construction equipment contributed 11 percent of statewide NOx emissions and 5 percent of VOC in 2005.[3]

Construction equipment is thus a significant contributor to total air pollutant emissions. Nevertheless, the actual harm from these emissions is far lower than UCS claims:

• Laboratory studies indicate that current, historically low levels of air pollution are at worst a minor factor in people’s health.[4] Health researchers have been unable to kill laboratory animals even with particulate matter at concentrations many times greater than the most polluted California air. Laboratory studies with human volunteers, including asthmatics, have not found harm from PM2.5 even at concentrations a few times greater than the highest real-world levels. This is true even for components of PM, such as diesel soot, that would be expected to have the highest toxicity. UCS does not mention or include any of this evidence in its report.
  
  
• Instead, UCS bases its health claims on the results from a much weaker type of study design called an "observational" epidemiology study. Observational studies work with non-randomly selected subjects and non-randomly assigned pollution exposures and then use statistical techniques to try to remove the biases inherent in non-random data. Unfortunately, a range of evidence shows that observational studies are unreliable and tend to create an appearance of risk where no risk in fact exists. UCS does not mention the weaknesses in its chosen form of evidence. Furthermore, even with their inherent biases, many observational studies have not found any harm associated with air pollution, yet UCS omits this contrary evidence from its analysis as well.
  
  
• UCS assumes that NOx emissions from construction equipment increase ozone, but in fact NOx emissions reduce ozone. A range of air pollution research has shown that when the ratio of VOC to NOx in air is relatively low--a condition typical in California’s metropolitan areas--reducing NOx increases ozone, and vice versa. The key evidence is that total NOx levels decline substantially on weekends, mainly due to reductions in the use of diesel trucks and construction equipment, but ozone levels rise.
  
  
• UCS exaggerates Californians’ exposure to air pollution. For example, UCS claims "more than 90 percent of Californians live in areas that do not comply with the federal ozone standard." The real percentage is only one-third of what UCS claims. UCS generated its exaggerated value by counting "clean" areas as "dirty." For example, even though 99 percent of people in San Diego County live in areas that comply with the federal 8-hour ozone standard, UCS counts all 3 million San Diegans as living in an area that violates the standard. Thus, in addition to exaggerating the harm from any given level of air pollution, UCS also exaggerates the air pollution levels themselves.

At high enough concentrations diesel exhaust can be an unpleasant and aggravating nuisance. But this is a far cry from UCS’s accusation that more than a thousand people are killed each year or that hundreds of thousands suffer serious harm from construction-related emissions.

UCS has vilified the Bush administration, sometimes with good reason, for manipulating scientific research for political purposes, and has even created a whole campaign and Web site to expose and condemn the politicization of science. Yet, in Digging Up Trouble UCS itself puts on a clinic in the selective use of scientific evidence to reach predetermined conclusions and support extra-scientific political goals.[5] The remainder of this commentary provides a more detailed critique of UCS’s misleading account of the health effects of current, historically low air pollution levels.[6]

Joel Schwartz is a visiting scholar at AEI.

 Click here to view the complete article as an Adobe Acrobat PDF.

Notes

1. Union of Concerned Scientists, Digging Up Trouble: The Health Risks of Construction Pollution in California (Berkeley, CA: December 2006), http://www.ucsusa.org/assets/documents/clean_vehicles/Digging-up-Trouble.pdf.

2. These percentages include only exhaust emissions. CARB also estimates that dust kicked up by "construction and demolition" accounted for about 5 percent of direct PM2.5 emissions. Presumably some of these emissions are due to the movement of construction equipment on unpaved surfaces. It doesn’t appear that UCS included these emissions in its estimates. 2005 is the year for which UCS estimated the health impacts of air pollution from construction equipment. California Air Resources Board, "Forecasted Emissions by Summary Category," last updated February 2, 2006, http://www.arb.ca.gov/app/emsinv/ccos/fcemssumcat_cc214.php; California Air Resources Board, "California Off-Road Diesel Fueled Equipment Inventory," October 2006, http://www.arb.ca.gov/msprog/ordiesel/documents/tier_distribution_table.pdf.

3. Ibid.

4. Air pollution has been dropping for as long as we’ve been measuring it—which means since the early or mid 1900s in some cases. California and national air pollution emissions and ambient concentrations are at historic lows and continue to decline. For summary national trends in air pollution levels from 1980-2005, see www.epa.gov/airtrends and click on any of the pollutants for a trend graph. For California ozone and PM10 trend data, see http://www.arb.ca.gov/adam/cgi-bin/db2www/polltrendsb.d2w/start. For California air toxics (i.e., benzene, 1,3-butadiene) trend data, see http://www.arb.ca.gov/adam/toxics/toxics.html. Some areas, including Los Angeles and Pittsburgh, have data going back to the early- or mid-20th Century. See, for example, C. I. Davidson, "Air Pollution in Pittsburgh: A Historical Perspective," Journal of the Air Pollution Control Association 29 (1979): pp. 1035-41; J. H. Ludwig, G. B. Morgan and T. B. McMullen, "Trends in Urban Air Quality," EOS 51 (1970): pp. 468-75; H. W. Ellsaesser, "Trends in Air Pollution in the United States," in The State of Humanity, ed. J. L. Simon (Malden, MA: Blackwell, 1995), pp. 491-502.

5. For more detailed discussions of popular portrayals of evidence on air pollution levels and health effects, see, for example, J. Schwartz, Air Quality: Much Worse on Paper Than in Reality (Washington, DC: American Enterprise Institute, May 2005), http://www.aei.org/docLib/20050602_EPOMay_Junenewg%282%29.pdf; J. Schwartz, Air Pollution and Health: Do Popular Portrayals Reflect the Scientific Evidence? (Washington, DC: American Enterprise Institute, May 2006), http://www.joelschwartz.com/pdfs/AirPoll_Health_EPO_0506.pdf; J. Schwartz, "Air Pollution: Why Is Public Perception So Different from Reality?" Environmental Progress 25 (2006): pp. 291-97.

6. See note 4 for summary information on air pollution trends.