Regional Haze Rule Guidance Tracking Progress Natural Levels

Regional Haze Rule Guidance: Tracking Progress & Natural Levels Overview of the concepts currently envisioned by EPA working groups by Marc Pitchford; August 2001

Tracking Progress: Regional Haze Rule Constraints • Haze metric – Haziness in deciview units – Determined from aerosol species concentrations – Mean of the 20% best & the 20% worst days each year averaged for 5 years • Progress determination – 5 -year mean best days should not degrade – 5 -year mean worst days should improve at the SIPidentified rate – Baseline period 2000 -2004 is compared with each separate 5 -year period thereafter

Tracking Progress: Guidance Document Topics • Calculation of haze metric – Data requirements • Parameters - IMPROVE species data to determine 6 major aerosol components • Completeness - all 6 components are needed • Substitution for missing components – mean value substitution if demonstrated that the haze values are not affected much – Approach to handle humidity effects on haze • Site-specific monthly adjustment values from historic RH data • Humidity adjustments applied to sulfate & nitrate species only

Tracking Progress: Guidance Document Topics • Calculation of haze metric (continued) – Algorithm to calculate daily extinction -- Algorithm to calculate deciview

Tracking Progress: Guidance Document Topics • Determination of mean of best & worst 20% – Completeness requirements for each year & for five year means – Approaches to deal with completeness deficiencies • Development of the progress goals • Utility of tracking trends in aerosol species trends

Natural Haze Levels Guidance: Regional Haze Rule Constraints • Clean Air Act national goal is to prevent future & remedy existing man-made visibility impairment • Natural haze is what is left when man-made impacts have been eliminated (the goal) – natural levels reflect contemporary conditions & land use patterns, not historic conditions • Reasonable rate of progress must be determined by considering the constant rate needed to bring worst day current conditions to estimated natural levels in 60 years

Natural Haze Levels Guidance: Estimation Approaches • Default approach – Based on natural levels of the six aerosol components estimates for the East & the West, taken from the NAPAP State of Science Report (1990) – Uses same algorithms & humidity adjustments as in the Tracking Progress Guidance – Statistical adjustment of the annual average dv values to the best & worst day values assumes normal distributions of natural conditions with known standard deviation – Default approach has already been applied to every class I area & will be provided in the guidance

Default Approach for Estimating Natural Haze Conditions

Natural Haze Levels Guidance: Estimation Approaches • Refined default approach (must be based on credible technical information) --- Options are: – Improved annual average natural concentration estimates for any of the 6 major aerosol species – Use of temporally varying natural concentrations estimates (e. g. seasonally, by sample period, or for extreme natural events) for any of the 6 aerosol species – All approaches must use the same algorithms for estimating natural levels as used for tracking progress

Natural Haze Levels Guidance • Advantages of the default approach – No states assessment required to adopt – Default values are good enough where current levels are much higher than estimated natural conditions • Advantages of the refined default approach – Permits better accounting of regionally-specific natural sources (e. g. ocean aerosol at coastal sites) – Can account for variations in natural emissions – Incorporates more recent technical information • States can improve their natural haze estimates, as needed, with any of their SIP submittals

Regional Haze Rule Guidance: Tracking Progress & Natural Levels • Public review drafts for both guidance documents are anticipated by early October 2001.