Transcript Regional Haze Rule Guidance: Tracking Progress & Natural

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
Rate To Achieve Natural Conditions in 60 Years
Example
Baseline
29
(Visibility impairment
on 20% worst days,
in deciviews)
Estimated
Natural
11
2000-4
x
Required Analysis for
1st Implementation
Period = 4.2 deciviews
x
Ultimate CAA goal
2018
2064
Year
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
bext  (3) f ( RH )[SULFATE ]  (3) f ( RH )[ NITRATE ]
 (4)[OMC]  (10)[ LAC]  (1)[SOIL]  (0.6)[CM ]  10
-- Algorithm to calculate deciview
dv  10 ln(bext / 10)
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
Long-term NWS
Avg. Relative Humidity
Estimates for Each
Class I Area
NAPAP Estimates
of Annual Average
PM Mass by
Component
IMPROVE
Methodology
- Ext. Efficiencies
- Rel. Humidity
Factor
Statistical Technique for Developing Worst
and Best Day Estimates from Annual Avg. Values
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.