IMPROVE Algorithm for
Estimating Light Extinction
Draft Recommendations to the
IMPROVE Steering Committee
Current IMPROVE Algorithm
bext  3  f ( RH )  Sulfate
 3  f ( RH )  Nitrate
 4  Organic Carbon
 10  Elemental Carbon
 1 Fine Soil 
 0.6  Coarse Mass 
 10
Assumptions include that
• Six particle component terms plus a constant Rayleigh scattering term are
sufficient for a good estimate of light extinction;
• Constant dry extinction efficiency terms for each of the six particle
components works adequately for all locations and times; and
• Light extinction by the individual particle components can be adequately
estimated as separate terms (like externally mixed components).
Reasons for Revision
• Regional Haze Rule utilizes the IMPROVE
algorithm for calculating the RHR index
– Haze index is in deciview (a logarithmic
transformation of light extinction)
– Calls for improvement in 20% worst haze to natural
levels by 2064
– Rate of progress for each 10-year SIP period is linear
between current and natural haze levels
– So haze estimates need to be good at the upper and
lower extremes, should have no fixable biases and
should include all important contributions even if
exclusively from natural sources
350
300
IMPROVE Bsp
250
200
150
100
50
0
0
50
100
150
200
Measured Bsp
250
300
350
Recommended Revised IMPROVE Algorithm
(Changed terms are in Bold Font)
bext  2.2  fS(RH)  Small Sulfate  4.8  fL(RH)  Large Sulfate
 2.4  fS(RH)  Small Nitrate  5.1 fL(RH)  Large Nitrate
 2.8  Small Organic Carbon  6.1 Large Organic Carbon
 10  Elemental Carbon
 1 Fine Soil 
 1.7  fSS(RH)  Sea Salt
 0.6  Coarse Mass 
 RayleighScattering( S ite Specific)
 0.33 NO2(ppb)
where L arge Sulfate 

Total Sulfate  Total Sulfate, for Total Sulfate  20
20
Large Sultate  Total Sulfate, for Total Sulfate  20
Small Sulfate  Total Sulfate  Large Sulfate
and nitrate and organic are split using the same process
Split Component Extinction Efficiency Model
for Sulfate, Nitrate, and Organic components
Split of Small & Large Sulfate Concentrations
versus
Total Sulfate Concentration
Overall Extinction Efficiency vs. Total Mass
30
5
4.5
4
Dry Extinction Efficiency
Component Sulfate Concentration
25
20
15
3.5
3
2.5
2
1.5
10
1
0.5
5
0
0
0
5
10
15
20
25
30
Sulfate concentration (ug/m 3)
0
5
10
15
20
25
30
Sulfate concentration (ug/m3)
• Small size dominates at low concentrations,
while large size dominates at high
concentrations
• Small size is likely young aerosol produce by
homogenous gas to particle processes.
• Large size is likely aged aerosol involving
cloud processing.
• Composite dry extinction efficiency
varies linearly from 2.2 to 4.8m2/g
• Small: Dg = 0.2μm & g = 2.2
• Large: Dg = 0.5μm & g = 1.5
• Different size distributions dictate
different water grow function, f(RH)
Water Growth Curves
10
9
8
7
f(RH)
6
fS(RH)
fL(RH)
Original
fSS(RH)
5
4
3
2
1
0
0
10
20
30
40
50
60
Relative Humidity (% )
70
80
90
100
Other New or Revised Terms
• Organic Compound Mass to Organic Carbon
Mass Ratio changed from 1.4 to 1.8
• Sea Salt = 1.8 x [Chlorine] and has its own
water growth term fSS(RH). Important at coastal
locations
• Rayleigh Scattering is calculated for the
monitoring site elevation and annual mean
temperature and integer rounded. Ranges from
8Mm-1 at 10,000’ to 12Mm-1at sea level
• NO2 light absorption in the visible is included
for sites that have such data (not routinely
available at IMPROVE sites)
350
Split Component Method Bsp
300
250
200
150
100
50
0
0
50
100
150
200
Measured Bsp
250
300
350
Normalized Bias for all data
1
0.8
0.6
Current
0.4
New
0.2
0
Overall
Top 20%
Mid 60%
Bottom 20%
-0.2
Bias = (estimated – measured)/measured
Normalized Bias for MANE-VU Sites
Normalized Bias for CENRAP Sites
1
0.8
0.7
0.8
0.6
0.5
0.6
0.4
Current
0.3
New
New
0.2
0.2
0.1
0
-0.1
Current
0.4
0
Overall
Top 20%
Mid 60%
Bottom 20%
Overall
Top 20%
Mid 60%
Bottom 20%
-0.2
-0.2
Normalized Bias for VISTAS Sites
Normalized Bias for WRAP Sites
0.7
1.2
0.6
1
0.5
0.8
0.4
0.3
Current
0.6
Current
0.2
New
0.4
New
0.1
0.2
0
-0.1
-0.2
Overall
Top 20%
Mid 60%
Bottom 20%
0
-0.2
Overall
Top 20%
Mid 60%
Bottom 20%
Implementation Steps for
Regional Haze Rule Application
• IMPROVE Steering Committee approval – 11/05
• Calculation of water growth functions for monthly
& annual averaged conditions for each
monitoring site – SAIC task-1 to 2 months
• Recalculation of current (5-year baseline) and
natural haze levels – VIEWS-1 month
• EPA modifies the regional haze guidance, so
states can choose – 6 to 12 months
• VIEWS will support both versions of the
algorithm for the foreseeable future