EPA designated the following counties as marginal nonattainment for ozone:
Carbon, Lehigh, Northampton, Lancaster, Bucks, Chester, Delaware, Montgomery, Philadelphia, Allegheny, Armstrong, Beaver, Butler, Fayette, Washington, Westmoreland and Berks.
The counties of Allegheny, Delaware and Lebanon are classified by the EPA as moderate nonattainment for PM2.5. Moreover, Allegheny County is classified moderate maintenance for PM10.
ERCs are available for six different pollutants:
| Pollutant | Major stationary source threshold for a facility where all pollutants are in attainment except for ozone |
Major stationary source threshold for a facility in severe ozone nonattainment |
| Nitrogen oxides (NOx) | >100 tons/year | >25 tons/year |
| Volatile organic compounds (VOC) | >50 tons/year | >25 tons/year |
| Sulfur oxides (SOx) | >100 tons/year | >100 tons/year |
| Carbon monoxide (CO) | >100 tons/year | >100 tons/year |
| PM10 | >100 tons/year | >100 tons/year |
| PM2.5 | >100 tons/year | >100 tons/year |
To satisfy offset requirements, new or modified major facilities in nonattainment areas must obtain ERCs to satisfy the offset ratio requirements for proposed emission increases. The offset ratios for marginal nonattainment area for ozone is 1.1 to 1. That means if 100 tpy of VOCs are emitted from a proposed new or modified major facility in the counties of Carbon, Lehigh, Northampton, Lancaster, Bucks, Chester, Delaware, Montgomery, Philadelphia, Allegheny, Armstrong, Beaver, Butler, Fayette, Washington, Westmoreland and Berks, which were classified as marginal nonattainment for ozone, the facility must obtain 110 tpy of ERCs to offset the increase in VOC emissions.
On the other hand, offset ratio for a moderate nonattainment area for PM2.5 is 1.15. Thus, for 100 tpy of PM2.5 emitted from a proposed new or modified major facility in the counties of Allegheny, Delaware and Lebanon, the facility must obtain 115 tpy of ERCs to offset the increase in PM2.5 emissions.
PA ERCs can be transferred from a dirtier area to a cleaner area only. ERCs created in the five Philadelphia counties (Bucks, Chester, Delaware, Montgomery and Philadelphia), may be transferred to users in the five-county area with some limitations. ERCs are generated anywhere else in the state may be transferred anywhere within Pennsylvania except the five counties in Philadelphia area.
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