Avoiding compliance pitfalls: understanding the overlap between HAPs and VOCs
Understanding how hazardous air pollutants (HAPs) and volatile organic compounds (VOCs) are counted is key to accurate reporting and staying in compliance. These pollutants often overlap, but how they are treated depends on the situation – especially when comparing emission inventories to permitting rules. Misunderstanding the differences can lead to underreporting, permit mistakes, and other compliance problems. This article will also discuss how state rules can make things more complex.
Emission inventories: often counted together
Emission inventories help regulatory agencies track actual emissions from facilities over time. These records support air quality models, guide policy, and help protect public health.
In many cases, HAPs that are also VOCs (like toluene or xylene) are included in the total VOC count. For example, the U.S. Environmental Protection Agency (EPA) includes HAP-VOCs in its National Emissions Inventory (NEI), which supports regional air quality models like the Community Multiscale Air Quality (CMAQ) system.
Frequently Asked Question: What is the National Emissions Inventory?
As an example, the Texas Commission on Environmental Quality (TCEQ) recommends using conservative “first cut” estimates for both VOCs and HAPs. This makes early reporting easier and helps avoid underestimating emissions.
Potential to emit (PTE): counted separately
PTE calculations are used to determine a facility’s regulatory status—such as whether it qualifies as a major source under New Source Review (NSR) or Title V or is subject to Maximum Achievable Control Technology (MACT) standards.
In this context, HAPs and VOCs are counted separately because they are subject to different thresholds:
- HAPs: 10 tons per year (TPY) for a single HAP, or 25 TPY for total HAPs.
- VOCs: Typically 100 TPY for major source classification under New Source Review (NSR), though this can vary by attainment status.
This separation is critical. A facility might exceed the HAP threshold and trigger MACT requirements, even if its VOC emissions are below NSR thresholds—or vice versa. As an example, if a paint booth has the potential to emit 500 pounds of toluene, this is counted as 500 pounds of HAP and 500 pounds of VOC. Even though that seems like double-counting for the same emission, it is important to include in both totals separately.
State-by-state variability
While federal rules provide a baseline, states often have their own interpretations and requirements:
- Ohio: Offers detailed guidance on calculating VOC and HAP emissions separately for permitting purposes. Facilities must demonstrate compliance with both sets of thresholds.
- Texas: Uses a tiered approach. Facilities begin with conservative estimates and refine them only if emissions approach regulatory thresholds.
- California: Maintains stricter standards and often requires separate reporting for toxic air contaminants (TACs), which include many HAPs. The state’s Air Toxics Hot Spots Program adds another layer of complexity.
Why the distinction matters
Failing to understand how HAPs and VOCs are counted can lead to serious compliance issues:
- Permitting errors: Misclassification can result in incorrect permit applications or missed regulatory obligations.
- Underreporting risks: Facilities may inadvertently underreport emissions if they assume HAPs are always included in VOC totals.
- Modeling impacts: While combined inventories help with regional modeling, they may obscure the risks posed by individual pollutants.
Recommendations for facilities
To stay compliant and avoid costly mistakes:
- Check state guidance: Requirements vary widely. Always consult your state environmental agency.
- Use Safety Data Sheet (SDS) data: Identify both VOC and HAP content in raw materials.
- Maintain separate records: Especially for PTE calculations, keep VOC and HAP data distinct.
- Consult experts: When in doubt, seek help from J. J. Keller & Associates subject matter experts using the Expert Help feature.
Key to Remember: The way HAPs and VOCs are counted depends heavily on context. Understanding these distinctions – and how they vary by state – is key to maintaining compliance and protecting air quality.