Increment Tracking

PSD stands for Prevention of Significant Deterioration, a federal permitting program for large facilities such as mines, power plants, and chemical plants. PSD permits are issued in one of three ways:

• By a state or local air agency through its approved State Implementation Plan (SIP)
• By a state or local agency using federal PSD rules in Title 40 CFR Part 52.21
• Directly by the U.S. EPA using those same federal rules

Nevada uses the delegated federal PSD program.

A major part of PSD is evaluating increment consumption. Increment is the maximum increase allowed for certain air pollutants above a “baseline” concentration. These increments exist for:

• PM10 (24 hour and annual)
• NOx (annual only)
• SO₂ (3 hour, 24 hour, and annual)

To understand how much increment is used, the first step is knowing the baseline concentration, which is the air quality level before the first PSD permit application is submitted in an area. Any increase above that baseline is considered “increment consumed.”

Increment tracking begins when a baseline date is triggered. There are two types:

1. Major source baseline date — set automatically by federal rules
2. Minor source baseline date — triggered when a PSD application is submitted and found complete

The minor source baseline date has the biggest effect on future growth. Once this date is set, all changes at all sources — including smaller industrial facilities, area sources, and mobile sources — must be counted in increment consumption for the affected pollutants.

The baseline area includes:

• The planning area where the new major source or major modification is located
• Any neighboring planning area where that project causes a significant air quality impact

Nevada’s planning areas are defined by the State Engineer’s hydrographic areas — more than 250 areas statewide. One PSD application can trigger baseline dates in several planning areas.

• Download Nevada’s Hydrographic Areas
• Download Nevada’s PSD Triggered Planning Areas

• Download Increment Tables

Federal rules (40 CFR 52.21(c)) define the maximum allowed increase above baseline concentrations. These standards differ by area type:

• Class I – strictest protection (Jarbidge Wilderness Area in Nevada)
• Class II – most of Nevada
• Class III – areas set aside for industrial growth (none designated in Nevada or nationwide)

EPA’s Method

Increment can’t be measured directly with air monitors. Instead, it is evaluated using air quality models. Two emissions inventories are compared:

• Baseline inventory – actual emissions on the minor source baseline date
• Current inventory – emissions from all sources after the baseline date

The change in emissions is modeled, and the results are compared to increment standards.

Nevada’s Method

Nevada uses a concentration difference approach:

1. Model baseline concentrations at each receptor point
2. Model current concentrations
3. Subtract baseline from current values

This difference shows whether increment was consumed or expanded.