Psd Calculation Example

Calculate Potential to Emit (PTE) and Prevention of Significant Deterioration (PSD) thresholds with our expert tool

Comprehensive Guide to PSD Calculations

The Prevention of Significant Deterioration (PSD) program is a key component of the Clean Air Act that helps protect air quality in areas that meet or are cleaner than the National Ambient Air Quality Standards (NAAQS). Understanding PSD calculations is essential for facility operators, environmental consultants, and regulatory professionals.

What is Potential to Emit (PTE)?

Potential to Emit (PTE) represents the maximum capacity of a stationary source to emit a pollutant under its physical and operational design. PTE is calculated based on:

• Maximum rated capacity of the source
• Maximum operating hours (typically 8,760 hours/year for continuous sources)
• Maximum emission rate without considering control devices
• Any federally enforceable limits on operations or emissions

PSD Applicability Thresholds

The EPA establishes two types of thresholds for PSD applicability:

1. Major Source Threshold: 250 tons per year (tpy) for any regulated pollutant, or 100 tpy for any of 28 listed source categories
2. Significant Emission Rates: Vary by pollutant (e.g., 40 tpy for PM2.5, 100 tpy for SO₂)

PSD Significant Emission Rates for Common Pollutants

Pollutant	Significant Emission Rate (tpy)	Major Source Category (tpy)
PM2.5	10	100
PM10	15	100
SO₂	40	250
NO₂	40	250
VOC	40	250
CO	100	250

Step-by-Step PSD Calculation Process

Calculating PSD applicability involves several key steps:

1. Determine Baseline Emissions:

   Calculate current actual emissions from all emissions units at the facility. This includes:

   • Actual measured emissions
   • Allowable emissions under current permits
   • Any emissions increases from recent modifications
2. Calculate Project Emissions:

   Estimate the emissions increase from the proposed project using:

   • Maximum rated capacity
   • Maximum operating hours
   • Emission factors from AP-42 or stack tests
   • Control device efficiencies
3. Determine Net Emissions Increase:

   Subtract any creditable emissions decreases from the project emissions increase. Creditable decreases must be:

   • Enforceable
   • Surplus to requirements
   • Permanent
   • Quantifiable
4. Compare to Significant Levels:

   Check if the net emissions increase exceeds:

   • Significant emission rates for the pollutant
   • Major source thresholds (100/250 tpy)

Common Calculation Methods

Facilities typically use one of these approaches to calculate PTE:

Comparison of PTE Calculation Methods

Method	Description	Advantages	Limitations
Actual Emissions	Based on measured emissions data	Most accurate for existing sources	May not reflect maximum potential
Permit Limits	Uses allowable emissions from permits	Legally defensible	May be artificially low
Emission Factors	Uses published factors (e.g., AP-42)	Good for new sources	May not reflect actual operations
Engineering Calculations	Based on process parameters	Tailored to specific operations	Requires expert knowledge

Key Regulatory Considerations

Several important regulatory factors affect PSD calculations:

• Netting: The process of combining emissions increases and decreases across a facility to determine the net change. The EPA’s netting rules allow facilities to offset increases with decreases from other units.
• Baseline Actual Emissions: The average rate of emissions over a 24-month period preceding the permit application, which serves as the reference point for determining increases.
• Federally Enforceable Limits: Restrictions on emissions or operations that are legally binding and can be used to limit PTE calculations.
• Plantwide Applicability Limits (PALs): Site-specific emissions caps that can provide operational flexibility while ensuring compliance.

Best Practices for Accurate Calculations

To ensure accurate and defensible PSD calculations:

1. Use the most recent and representative emissions data available
2. Document all assumptions and calculation methodologies
3. Consult the latest version of EPA’s AP-42 emission factors
4. Consider all potential operating scenarios (startup, shutdown, malfunction)
5. Engage qualified environmental professionals for complex facilities
6. Maintain detailed records to support all calculations
7. Regularly review and update calculations as operations change

Common Mistakes to Avoid

Facilities often make these errors in PSD calculations:

• Using outdated emission factors or incorrect AP-42 sections
• Failing to account for all emissions units at the facility
• Incorrectly applying control device efficiencies
• Overlooking startup, shutdown, and malfunction emissions
• Misapplying netting provisions or creditable decreases
• Not properly documenting calculation methodologies
• Ignoring state-specific requirements that may be more stringent

Resources for Further Information

For authoritative information on PSD calculations:

• EPA New Source Review (NSR) Program – Official EPA page with comprehensive NSR/PSD information
• EPA AP-42 Emission Factors – Database of emission factors for various industries
• CFR Title 40 Part 52 – The actual regulatory text for PSD requirements