ently monitors national ambient concentrations for few of the 188 air toxins identified in the Clean Air Act Amendments. Rather, the agency sets technology-based performance standards to control emissions of these substances. As a result, EPA has only begun developing a National Toxins Inventory.
Although a great deal of work has been done on valuing components of air quality, there is currently no comprehensive measure of the economic impacts of air pollution for the United States. However, a recent EPA study evaluating the economic costs and benefits of clean air regulations provides a useful benchmark that sheds light on this issue (U.S. Environmental Protection Agency, 1997). The estimates given are subject to many uncertainties due to the difficulty of estimating exposure and the incidence of effects related to exposure and valuing the effects. In addition, data on air toxins have only recently become available, making it difficult to develop comparable estimates for these pollutants. The EPA study includes no physical or monetary assessments of the impacts of changes in air quality on ecosystem health, physical capital, or global public goods, such as slowing climate change and preventing ozone depletion. Moreover, many of the estimates of benefits, particularly those involving the valuation of health benefits and the discount rate, have been the subject of major criticism (see Clean Air Act Council on Compliance, 1997).
Notwithstanding these limitations, the EPA study provides an indication of the overall economic importance of changes in air quality, as well as a sense of the relative importance of the various air pollutants and the impacts on different sectors. The study estimates the economic benefit of actual air pollution relative to a counterfactual baseline that assumes no controls imposed after 1970; roughly speaking, the counterfactual is for emissions to grow with the economy, rather than declining as described above. The major result presented is that the economic benefits of reduced air pollution in 1990 are estimated to be worth $1,248 billion. Reduced mortality benefits ($1,004 billion) account for 80 percent of this total; together, avoided human health effects account for 99 percent of the total. In addition, benefits of improved visibility are estimated at $3.4 billion, those of reduced household soiling at $4.0 billion, and those of increased agricultural income from reduced yield losses due to ozone at about $1.0 billion. With regard to specific pollutants, most of the benefits are attributed to reductions in particulate matter (PM-10) and lead; the benefits of ozone reduction are estimated to be only on the order of $2 billion.