Comparative Analysis of 2005-09 '1st Progress Period' and 2000-04 'Baseline' Regional Haze Rule Metrics

摘要

The U.S. Environmental Protection Agency (EPA) established the Regional Haze Rule to achieve the national visibility goal established by the Clean Air Act that called for the virtual elimination of anthropogenic visibility impairment in 156 class Ⅰ areas (CIA). The RHR requires periodic state implementation plans (SIPs) from each state to demonstrate "reasonable progress" toward achieving RHR-defined natural visibility conditions by a target date of 2064. RHR implementation guidance requires states to determine the uniform rate of haze reduction that would result in reaching the estimated natural haze level from current conditions on the annual 20% most impaired visibility days for each protected area. States must also show that the five-year mean of the annual 20% least impaired visibility conditions at each protected area do not degrade. Progress towards the RHR goal of eliminating manmade impairment in class Ⅰ areas is to be tracked by comparing discreet five year means of these haze metrics with the baseline period being from 2000-2004 and the first tracking progress period ("period 1") being 2005-2009. In this paper, period 1 regional haze metrics are compared to the baseline and estimated natural conditions. A case study is presented to illustrate some of the issues that arise when calculating and interpreting the RHR metrics. More detailed information for each of the 110 IMPROVE Regional Haze Tracking Sites (RHTS) which represent 155 CIAs can be found in Chapter 9 of the 2011 IMPROVE Report Ⅴ.