The Environmental Protection Agency (EPA) has not traditionally taken an aggressive approach to the regulation of hazardous air pollutants (HAPs).  HAPs are toxic emissions (such as benzene), generally from industrial sources, that are usually emitted at much lower levels than “criteria” pollutants (such as ozone), but which tend to be more toxic.  EPA has only recently begun the process of promulgating standards addressing the “residual risks” of HAPs, which refers to the long-term health consequences of exposure to such chemicals.  All indications suggest that EPA will base the new standards on risk models derived from traditional static source monitoring.  Professor McGarity argues that such an approach will be inadequate to address the problem of migrating toxic hot spots, and that the health threats posed by HAPs can only be addressed effectively by a data-driven approach employing mobile real-time monitoring technology.

Professor McGarity suggests that the experiences of the mobile air-monitoring labs run by the Texas Commission for Environmental Quality (TCEQ) demonstrate not only that mobile real-time monitoring can be deployed effectively, but also that such an approach is necessary to obtain an accurate view of the real health threats posed by HAPs.  Beginning in 1988, TCEQ teams in vans equipped with ambient-air-quality monitoring equipment sought to measure the real-time exposure of residential communities to HAPs emitted from petrochemical refining facilities in Texas City and the Golden Triangle area in southeast Texas.  Generally responding to reports of strange smells in the areas around the facilities, the teams took measurements in a variety of locations and were able to follow in real time the dispersion of plumes of emissions emanating from the refineries.  The mobile labs were able to pinpoint the timing and location of emissions with far greater accuracy than could the traditional static monitoring devices in the area.  More importantly, the mobile labs were able to detect intermittent and mobile plumes of pollutants—“migrating toxic hot spots” —that simply could not be detected by the static monitors.

The measurements of the mobile labs demonstrated that migrating toxic hot spots exist and that traditional monitoring approaches are inadequate to address them.  Given the toxicity and carcinogenicity of the chemicals detected, such as benzene and butadiene, and the proximity of the refineries to residential areas and schools, it appears that any residual-risk standard for HAPs that fails to address the problem of migrating toxic hot spots will inevitably fail to protect the public health from a significant form of exposure to HAPs.  If EPA continues to adhere to models based on traditional stationary monitoring technology instead of adopting modern mobile real-time monitoring approaches, its forthcoming residual-risk standards should be expected to fail in their central purpose of protecting the public health from HAP exposure.