Contribution of Chemical Constituents to Visibility...
Transcript of Contribution of Chemical Constituents to Visibility...
Contribution of ChemicalConstituents to Visibility Reduction
During the California RegionalPM10/PM2.5 Air Quality Study
Steven Heisler, ENSR InternationalCamarillo, CA
Presented at
AAAR Annual Meeting, October 22, 2003Anaheim, CA
Approach• Applied light extinction efficiencies to 24-hour
average particulate matter chemical composition datato estimate constituent contributions to the lightextinction coefficient
• Constituents included:Fine Soil = 1.89[Al] + 2.14[Si] +1.4[Ca] + 1.43[Fe]NH4NO3 = 1.29[NO3
-](NH4)2SO4 = 1.375[SO4
=]Organic Compounds (OCM) = 1.4[OC]Elemental Carbon (EC) = measured EC
Light Extinction Efficiencies
• Used 10 m2/g for light absorption by EC• Evaluated light scattering efficiencies developed for
IMS95 and for IMPROVE (Interagency Monitoring ofProtected Visual Environments) with 24-hour averagechemical composition, light scattering coefficient (bs),and relative humidity (RH) data from Fresno FirstStreet (FSF) site
• Chose FSF data because only site with open-air,unheated nephelometer (NGN-2)
IMS95 and IMPROVE LightScattering Efficiencies
Constituent IMS95(m2/g)
IMPROVE(m2/g)
Fine Soil 2 1NH4NO3 2.1/(1-RH)0.7 3f(RH)
(NH4)2SO4 2.1/(1-RH)0.7 3f(RH)OC 2.8/(1-RH)0.2 4
IMPROVE f(RH)
0
5
10
15
20
25
30
0 10 20 30 40 50 60 70 80 90 100
RH (%)
f(RH)
IMS95 and IMPROVE EfficienciesProduced Essentially Identical Results
IMPROVE vs. IMS95
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100
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400
500
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900
1000
0 100 200 300 400 500 600 700 800 900 1000
IMPROVE Calculated bs (Mm-1)
IMS9
5 Ca
lcul
ated
bs (
Mm
-1) Calc. = 1.00 Meas. - 1.33 Mm-1
R2 = 0.9999n = 54
IMPROVE Light Scattering Efficiencies
0
500
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2500
3000
3500
4000
0 500 1000 1500 2000 2500 3000 3500 4000
Measured bs (Mm-1)
Calc
ulat
ed b
s (M
m-1
)
Measured bs is Under-predicted,Especially at High Values
IMPROVE Light Scattering Efficiencies
0
100
200
300
400
500
600
700
800
900
1000
0 100 200 300 400 500 600 700 800 900 1000
Measured bs (Mm-1)
Calc
ulat
ed b
s (M
m-1
)
Calc. = 0.670 Meas. + 27.2 Mm-1
R2 = 0.977n = 48
Correlation is Good at Lower Values, butMeasured bs is Under-Predicted
Calculated Seasonal Adjustments toIMPROVE Efficiencies
• Only adjusted efficiencies for NH4NO3 and (NH4)2SO4
• Seasonal adjustment calculated as average of:(measured bs - soil bs - OCM bs) /(NH4NO3 bs + (NH4)2SO4 bs)
• Also calculated adjustment factor for high lightscattering (measured bs > 1000 Mm-1)
NH4NO3 and (NH4)2SO4 LightScattering Efficiency Adjustment
Factors
Season Adjustment FactorWinter (Dec. – Feb.) 2.17Spring (Mar. – May) 0.74
Summer (Jun. – Aug.) 0.81Fall (Sep. – Nov.) 1.51High Measured bs 5.09
Adjustment Improves AgreementAdjusted IMPROVE Light Scattering Efficiencies
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3500
4000
0 500 1000 1500 2000 2500 3000 3500 4000
Measured bs (Mm-1)
Calc
ulat
ed b
s (M
m-1
)
Calc. = 0.933 Meas. + 23.9 Mm-1
R2 = 0.919n = 54
Agreement Is Best at Lower ValuesAdjusted IMPROVE Light Scattering Efficiencies
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1000
0 100 200 300 400 500 600 700 800 900 1000
Measured bs (Mm-1)
Calc
ulat
ed b
s (M
m-1
)
Calc. = 0.929 Meas. + 9.5 Mm-1
R2 = 0.983n = 48
Application of Light ExtinctionEfficiencies
• Applied to 11 sites with annual relative humidity andPM2.5 chemical composition data
• Data available from 12/99 - 1/01• Calculated f(RH) for every hour and averaged over
24-hour filter sampling periods• “Capped” f(RH) at value for 95% relative humidity to
avoid “instabilities”• Did not apply adjustment for “high” values (i.e., only
used seasonal adjustment)
Merced
Sacramento
Stockton
Modesto
Fresno (3)Selma
Visalia
BakersfieldOildale
Seasonal Average Total Calculated Light Extinction
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100
200
300
400
500
600
700
800
900
Sacram
ento
Stockton
Modesto
Merced
Fresno-A
Fresno-B
Fresno-C
Selma
Visalia
Oildale
Bakersf
ield
Seas
onal
Ave
rage
Cal
cula
ted
Ligh
t Ext
inct
ion
(Mm
-1)
Winter Spring Summer Fall
Seasonal Average Total CalculatedLight Extinction Coefficient
• Winter average values are higher than other seasonsat all sites
• Fall average values are higher than spring or summer• Values are highest at Visalia, Merced and Modesto• Values are lowest at Sacramento and Stockton
Winter Constituent Contributions
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10
20
30
40
50
60
70
80
90
Sacram
ento
Stockton
Modesto
Merced
Fresno-A
Fresno-B
Fresno-C
Selma
Visalia
Oildale
Bakersf
ield
Perc
ent o
f Sea
sona
l Ave
rage
Lig
ht E
xtin
ctio
n
Ammonium Nitrate Organic Compounds Elemental Carbon Ammonium Sulfate Other
Fall Constituent Contributions
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10
20
30
40
50
60
70
80
Sacram
ento
Stockton
Modesto
Merced
Fresno-A
Fresno-B
Fresno-C
Selma
Visalia
Oildale
Bakersf
ield
Perc
ent o
f Sea
sona
l Ave
rage
Lig
ht E
xtin
ctio
n
Ammonium Nitrate Organic Compounds Elemental Carbon Ammonium Sulfate Other
Spring Constituent Contributions
0
5
10
15
20
25
30
35
40
45
Sacram
ento
Stockton
Modesto
Merced
Fresno-A
Fresno-B
Fresno-C
Selma
Visalia
Oildale
Bakersf
ield
Perc
ent o
f Sea
sona
l Ave
rage
Lig
ht E
xtin
ctio
n
Ammonium Nitrate Organic Compounds Elemental Carbon Ammonium Sulfate Other
Summer Constituent Contributions
05
101520253035404550
Sacram
ento
Stockton
Modesto
Merced
Fresno-A
Fresno-B
Fresno-C
Selma
Visalia
Oildale
Bakersf
ield
Perc
ent o
f Sea
sona
l Ave
rage
Lig
ht E
xtin
ctio
n
Ammonium Nitrate Organic Compounds Elemental Carbon Ammonium Sulfate Other
Seasonal Average ConstituentContributions
• NH4NO3 is largest contributor at all sites during winterand fall, accounting for about 60% to about 80%during winter and about 40% to about 70% during fall
• Organic compounds are largest contributor at mostsites during spring, accounting for about 30% toabout 40%, and at all sites during summer,accounting for about 30% to about 45%
• Elemental carbon is a significant contributor at mostsites during spring and summer, accounting for asmuch as 25%
Why is Winter Calculated LightExtinction Higher at Visalia, Mercedand Modesto than at Other Sites?
Winter Average NH4NO3 Concentrationsare Higher at Other Sites
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5
10
15
20
25
Sacram
ento
Stockton
Modesto
Merced
Fresno - A
Fresno - B
Fresno - C
Selma
Visalia
Oildale
Bakersf
ield
Win
ter A
vera
ge N
H4N
O3 (
ug/m
3 )
But Average f(RH) is Lower at Other Sites
Winter Average f(RH)
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Sacramento Stockton Modesto Merced Fresno &Selma
Visalia Bakersfield
Aver
age
f(RH)
Summary• Previously developed light scattering efficiencies
under-predicted measured light scattering, butseasonal adjustment factors improved agreement
• Calculated total light extinction is highest duringwinter and lowest during summer
• NH4NO3 is the largest contributor at all sites duringwinter and fall
• Organic compounds are the highest contributor atmost sites during spring and summer
• Winter average light extinction was higher at Visalia,Merced and Modesto than at other sites because ofhigher reported relative humidity