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Regulating Fine Particles

Developing a new paradigm for managing fine particulate air pollution.

Fortnightly Magazine - February 2012

total PM but give emphasis to particular components. Given the remaining uncertainty around the specific components of PM that are most toxic, the workshop participants thought the latter alternative would be the most workable.

Additionally, the majority of workshop participants believed that carbon-containing PM and possibly nickel would be the most likely candidates for component-specific regulation if such an approach were implemented.

Regulating Black Carbon

There are many carbon-containing compounds in PM. They are generally defined by the ways they are measured. Two major categories are black—or elemental—carbon (BC or EC), and organic carbon (OC). EPA, for example, is measuring these two categories at its Chemical Speciation Network monitoring sites. More health studies have considered black carbon than other measures of carbonaceous particles because BC can be easily measured by looking at light absorption of particles in the atmosphere. Black carbon has been associated with health impacts in many epidemiological studies, and it also plays a role in visibility impairment. Fewer studies have examined other categories of carbon-containing particles, such as organic carbon, but among them many have reported significant associations between these particles and health. The reality is that there are many different carbon-containing compounds, and some are more toxic than others. Clearly the available information isn’t sufficient to identify the toxicities of the many specific compounds, and thus it might be necessary to consider broad categories of carbon compounds in any initial regulatory approach to managing PM in the environment.

If a specific carbon standard were proposed, it would have direct and important implications for emitters, including electric power companies. The extent to which BC, OC, or a broader carbon-containing PM fraction—such as total carbon, or TC—are reduced will impact the ability of a specific region to satisfy mass-based standards. This in turn can affect the need to reduce other fractions of PM, such as sulfate or nitrate. As a result, research is needed to collect as much information as possible about the breadth of carbon-containing compounds that influence health, as well as how these compounds relate to readily available measures of carbon-containing compounds.

Health-Based Standards

The current health effects literature needs to be systematically reviewed and organized in an effort to determine which measures of carbon-containing compounds are most frequently and highly associated with health impacts. This involves epidemiological studies which include ambient measurements of carbon-containing compounds, as well as toxicological studies that may help elucidate the underlying biological mechanisms that could provide support for the observed associations. This evidence needs to then be weighed to determine whether it is of sufficient quality to be used in a regulatory context, which is the job of the scientific community and regulators such as EPA.

If the evidence is judged sufficient, then it will be necessary to identify the sources of these compounds and how emissions relate to ambient concentrations. The latter is likely to be quite complex because of potential atmospheric reactions that create new compounds; in this case it’s important to identify the precursors. As is the case currently with ozone, identifying the most important precursors would be critical