Site Specific Uncertainty in Regional Haze RuleHaze Indexes

In 1999, the US Environmental Protection Agency (EPA) published the regional haze rule (RHR). The RHR default implementation plan calls for each class I area 20% worst baseline (2000-2004) visibility to improve linearly in time to natural conditions in 2064 and in calendar year 2018, each class I area 20% worst visibility is to comply with the 2018 visibility that falls on the linear improvement glide path from baseline (2000-2004) to natural (2064) conditions. This study shows that accurately assessing compliance depends on assessing the uncertainty in baseline, natural and 2018 visibility estimates. This study identifies ±3 dV and ±4 dV of uncertainty in 20% worst natural and baseline visibility estimates. The percent uncertainty in calculated 2018 glide path visibility values ranges from 10% - 45%.