New Ultra Fine Particulate NAAQS in the (Not So Distant) Future?

The U.S. Environmental Protection Agency (U.S. EPA) has expressed that a revisit of existing particulate matter (PM) National Ambient Air Quality Standards (NAAQS) may result in a first-time NAAQS for “ultrafine” particles (UFP).  UFP is defined as PM with a diameter of less than 0.1 µm.  UFP in and of itself is not currently a regulated pollutant (other than being a component of PM_2.5) since the contribution of UFP to ambient air levels generally is considered negligible, as PM compliance is typically based on particulate mass and total contribution.  However, U.S. EPA has begun to feel pressure to reconsider a NAAQS UFP from various environmental groups, despite the historical absence of regulations, on the basis of the “constituent toxicities or unique physical attributes of UFPs.”  New PM NAAQS are required by law to be finalized by late 2017.  A review of the NAAQS will include an integrated science assessment (ISA), which reviews all relevant scientific studies; a risk and exposure assessment using the ISA to detail the health risks to humans from PM exposure; and, a policy assessment to determine the policy options for revising the existing NAAQS.  A previous review of the PM NAAQS in 2012, found that the link between UFP exposure and adverse health effects was “suggestive,” but not conclusive.

Unlike larger PM particles (specifically, PM₁₀ and PM_2.5), research on the adverse health effects of UFP is still in the very early stages.  One of the largest known contributors of UFP is roadway air pollution.  Initial research suggests that UFP, specifically resulting from vehicle emissions, may lead to low birth weight and IQs in children, and cardiovascular and pulmonary repercussions in both children and adults.  Research also suggests that due to its much smaller size, UFP can be absorbed deeper into the body and persevere longer than larger PM particles.  U.S. EPA has warned that research is very preliminary and limited to only diesel exhaust. With this in mind, U.S. EPA is hesitant to create UFP regulations, as premature regulations may lead to improper control of the constituents that result in the greatest adverse health effects.  However, the upcoming review of the existing PM NAAQS could spark the additional research and monitoring that is needed to fully understand the effects of UFP on human health, and therefore lead to U.S. EPA’s first UFP NAAQS.