June 7, 2023
10:00AM - 11:00AM
Derivation and Application of Comparison Values and Action Levels for Use in Mobile Air Monitoring
Dr. Sabine Lange, Chief Toxicologist, TCEQ
The Texas Commission on Environmental Quality (TCEQ) has several ambient air monitoring instruments that can collect instantaneous chemical concentration data during mobile monitoring trips. These instruments can provide accurate, real-time concentrations, typically in 1-30 second intervals, of select chemicals in ambient air while the monitoring vehicle is in motion. The measured levels can be used to rapidly identify abnormally high concentrations of targeted chemicals in ambient air and can help expedite efforts to address them. However, instantaneous data present unique challenges for interpretation, due in part to their very short sample duration. These challenges include a lack of relevant toxicity studies with brief exposure durations on which to base health risk determinations, as well as the need for continuous, real-time review of incoming air monitoring data to determine appropriate response actions. Based on evaluation of the data that TCEQ has collected with these instruments, together with new methods to relate existing toxicity values to instantaneous concentrations, the TCEQ developed six different types of fit-for-purpose data screening levels. These values are intended to provide guidance to mobile monitoring staff on when to initiate actions such as source investigation, stationary monitoring, and staff exposure mitigation (i.e., leaving the area). These values provide guidance for staff actions but are not intended to overrule the cautionary discretion of the monitoring and field investigation staff, particularly when considering exposure mitigation. Altogether, these fit-for-purpose comparison values can help the TCEQ and others to prioritize resources for identifying sources, characterizing chemical concentrations, and/or mitigating exposure from events that cause chemical releases.