Air Toxics Screening Tool
Air Quality Modeling
The client is a carpet manufacturing facility that operates several similar processing lines that apply finishes to the back of carpets. The finish being applied is dependent on a wide range of customer specifications, and thus a diverse mixture of finishes with different individual components is required. Customer demands often dictate that a new finishing material be entered into the production process, often times on a quick turnaround. Meeting customer needs is challenging in a state that requires complex air toxics modeling for any air toxics emissions increase or when any new air toxic not previously emitted is introduced to the production line. To address the need to perform frequent air toxics modeling quickly, the client needed a screening toxics modeling tool that could automatically and quickly quantify air toxics concentrations based on the entry of new finishes and their individual components.
ALL4 developed a screening tool using U.S. EPA’s AERMOD air dispersion model. Given the complexity of the facility and the various processing lines that are operated, the toxics screening tool needed to meet the following requirements:
- Assume that any new air toxic emissions or any emissions increase were being emitted from a single “worst case” stack.
- Incorporate all of the appropriate Georgia ambient concentration thresholds for any new toxics that may be emitted.
- Estimate ambient concentrations for all new air toxics based on the entry of a component list for new finishes being used and identify an hourly emission rate for all new air toxics being introduced.
ALL4 used AERMOD to model each process and associated stack at the facility separately using a unity emission rate (i.e., a 1 g/s emission rate from each stack), accounting for building downwash, meteorological, and other site-specific influences. A comparison was then made to determine which stack resulted in the highest ambient concentrations by itself. Any emissions increase or new air toxic being emitted could then be applied to that “worst case” stack to quickly predict ambient concentrations that were then automatically compared to the appropriate ambient concentration thresholds.
The result was a conservative toxics screening tool that could provide an immediate indication of whether a new finishing material would result in exceedances of the ambient concentration thresholds. If no exceedances are identified, then the finish can be introduced to the production line immediately. Only if exceedances were identified within the screening tool would a more time consuming refined modeling evaluation be performed. The tool that was developed and the conservatism that was built in allows the facility to quickly respond to customer demand with the assurance they are maintaining compliance with the air toxic regulatory requirements.