Most of the claimed benefits of federal regulation stem from air quality controls. Between 2006 and 2016, the Environmental Protection Agency (EPA) accounted for 71 percent of the monetized benefits and 55 percent of the costs of all major federal regulations. Of those benefits, 95 percent came from air quality rules, primarily those targeting fine particulate matter (PM2.5), microscopic airborne particles smaller than 2.5 micrometers in diameter.
Thus, the EPA decision to no longer quantify the benefits of PM2.5 emission reduction is important. The rationale offered by the EPA is “the E.P.A.’s analytical practices often provided the public with false precision and confidence regarding the monetized impacts of fine particulate matter (PM2.5) and ozone.”
What do we know about the benefits of PM2.5 reduction? David Kemp and I examined the issue last year. The central problem is that our estimates of the mortality risks associated with PM2.5 exposure rely on observational studies. Randomized controlled trials, the gold standard for demonstrating cause and effect, are not feasible. Instead, researchers rely on statistical methods that remain vulnerable to unobserved and unmeasured alternative causes of mortality other than PM2.5 exposure.
Despite these limitations, such studies continue to underpin federal standards. The EPA also assumes there is no safe threshold for PM2.5 exposure. This assumption is highly contested and may exaggerate the estimated benefits of regulation. In addition, the EPA treats PM2.5 as a uniform substance, even though it includes a wide range of particles with different levels of toxicity.
For example, coal ash or diesel exhaust may be far more harmful than dust from unpaved roads, but current standards treat them all equally. This one-size-fits-all approach can result in too little regulation in some areas and too much in others.
The costs and benefits of regulation are also unevenly distributed. Most of the health benefits are concentrated in a small number of urban counties, while some rural areas bear significant costs with few benefits. When scientific uncertainty and regional variation are taken into account in the analysis, PM2.5 regulation may result in negative net benefits in many parts of the country.