The Western Regional Air Partnership (WRAP) contracted with Air Resource Specialists, Inc. (ARS) to draft a short document summarizing the current status of Natural Conditions, as used in the context of the Regional Haze Rule (RHR). This document provides a summary of the progression and current status of these estimates, including the original EPA default estimates and the revised Natural Conditions II estimates. Also summarized here are considerations and recommendations for future Natural Condition refinements, and some recommended adjustments to regional haze management strategies.

Natural Conditions Status Summary and Recommendations Report (pdf) (0.5 MB)

Much of the documentation referenced in this report regarding methodologies, critical reviews, and current science related to Natural Conditions has also been assembled and archived in a separate online repository maintained by the WRAP.