Contribution of ChemicalConstituents to Visibility Reduction

During the California RegionalPM10/PM2.5 Air Quality Study

Steven Heisler, ENSR InternationalCamarillo, CA

Presented at

CRPAQS Data Analysis Workshop, March 10, 2004Sacramento, 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, particle light scatteringcoefficient (bsp), and relative humidity (RH) data fromFresno First Street (FSF) site

• Chose FSF data because only site with open-air,unheated nephelometer (NGN-2)

IMS95 and IMPROVE ConstituentLight Scattering EfficienciesConstituent 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)

Treatment of Hourly RH and bsp

• Calculated 24-hour average f(RH) and bsp

• Excluded hours with RH above 95% to avoid fog• Excluded days with less than 18 hours in average

Results with IMS95 and IMPROVEEfficiencies are Well Correlated, but

IMS95 is LowerIMS95 vs. IMPROVE

0

100

200

300

400

500

600

0 100 200 300 400 500 600

IMPROVE Calculated bsp (Mm-1)

IMS9

5 Ca

lcul

ated

bsp

(Mm

-1) IMS95 = 0.732 IMPROVE + 3.59 Mm-1

R2 = 0.992n = 49

Measured bsp is Under-Predicted

IMPROVE Light Scattering Efficiencies

0

200

400

600

800

1000

1200

0 200 400 600 800 1000 1200

Measured bsp (Mm-1)

Calc

ulat

ed b

sp (M

m-1

)

Calc. = 0.510 Meas. + 27.0 Mm-1

R2 = 0.983n = 48

Calculated Adjustment to 24-HourAverage IMPROVE f(RH)

• Calculated “apparent” f(RH) as:(measured bsp - soil bsp - OCM bsp) /(“dry” NH4NO3 bsp + “dry” (NH4)2SO4 bsp)

• Used results from linear regression of “apparent” 24-hour average f(RH) vs. 24-hour average IMPROVEf(RH)

"Apparent" f(RH) vs. IMPROVE f(RH)

-2.00

0.00

2.00

4.00

6.00

8.00

10.00

12.00

1.00 1.50 2.00 2.50 3.00 3.50

IMPROVE f(RH)

"App

aren

t" f(

RH)

App. = 2.94 IMP. - 2.57R2 = 0.740n = 48

Adjustment Improves AgreementAdjusted IMPROVE f(RH)

0

200

400

600

800

1000

1200

0 200 400 600 800 1000 1200

Measured bsp (Mm-1)

Calc

ulat

ed b

sp (M

m-1

)

Calc. = 0.804 Meas. + 23.5 Mm-1

R2 = 0.977n = 48

Comparison of Calculated bsp withRadiance Research (RR) Neph.

MeasurementsCalculated bsp vs. RR bsp

Valley Annual Sites

0

100200

300

400

500600

700

800900

1000

0 200 400 600 800 1000

Measured bsp (Mm-1)

Calc

ulat

ed b

sp (M

m-1

)

Agreement is Poor at Mojave Desert Sites

Calculated vs. Measured RR Nephelometer - China Lake

0

10

20

30

40

50

60

0 10 20 30 40 50 60

Measured bsp (Mm-1)

Calc

ulat

ed b

sp (M

m-1

)

Agreement is Poor at Mojave Desert Sites

Calculated vs. M easured RR Nephe lometer - Edwards AFB

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80

Measured bsp (Mm-1)

Cal

cula

ted

bsp

(Mm

-1)

Agreement is Poor at Mojave Desert Sites

Calculated vs. Measured RR Nephelometer - Olancha

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140 160 180

Measured bsp (Mm-1)

Cal

cula

ted

bsp

(Mm

-1)

Measured bsp is Moderately Correlatedwith PM2.5 Mass at Desert Sites

RR bsp vs. PM2.5 MassChina Lake, Edwards and Olancha

0102030405060708090

100

0 2 4 6 8 10 12 14 16 18 20

PM2.5 Mass Conc. (ug/m3)

b sp

(Mm

-1)

Reconstructed Mass is Higher thanMeasured Mass at Desert Sites

Reconstructed vs. Measured PM2.5 MassChina Lake, Edwards and Olancha

0

5

10

15

20

25

0 5 10 15 20 25

Measured PM2.5 Mass (ug/m3)

Reco

nstru

cted

PM

2.5

Mas

s (u

g/m

3 )

Calculated Organic Compound Mass(OCM) is Frequently Higher than

Measured PM2.5 Mass at Desert SitesOCM vs. Measured PM2.5 Mass

China Lake, Edwards and Olancha

0

5

10

15

20

25

0 5 10 15 20 25

Measured PM2.5 Mass (ug/m3)

OCM

(ug/

m3 )

Application of Light ExtinctionEfficiencies to SJV Sites

• 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• Excluded hours with RH above 95% to avoid fog

Merced

Sacramento

Stockton

Modesto

Fresno (3)Selma

Visalia

Bakersfield (2)Oildale

Seasonal Average Calculated Light Extinction

0

100

200

300

400

500

600

Sacram

ento

Stockton

Modesto

Merced

Fresno Firs

tFresn

o MV

Fresno R

esSelm

aVisa

liaOild

aleBak

ersfiel

d Ca

Bakersf

ield R

esCa

lcul

ated

bex

t (M

m-1

)

Winter Spring Summer Fall

Winter Constituent Contributions to Light Extinction

0102030405060708090

Sacram

ento

Stockton

Modesto

Merced

Fresno Firs

tFresn

o MV

Fresno R

esSelm

aVisa

liaOild

aleBak

ersfiel

d Ca

Bakersf

ield R

esPe

rcen

t of S

easo

nal A

vera

ge

Ammonium Nitrate Organic Compounds Elemental Carbon Ammonium Sulfate Other

Fall Constituent Contributions to Light Extinction

0

10

20

30

40

50

60

70

80

Sacram

ento

Stockton

Modesto

Merced

Fresno Firs

tFresn

o MV

Fresno R

esSelm

aVisa

liaOild

aleBak

ersfiel

d Ca

Bakersf

ield R

esPe

rcen

t of S

easo

nal A

vera

ge

Ammonium Nitrate Organic Compounds Elemental Carbon Ammonium Sulfate Other

Spring Constituent Contributions to Light Extinction

0

10

20

30

40

50

60

Sacram

ento

Stockton

Modesto

Merced

Fresno Firs

tFresn

o MV

Fresno R

esSelm

aVisa

liaOild

aleBak

ersfiel

d Ca

Bakersf

ield R

esPe

rcen

t of S

easo

nal A

vera

ge

Ammonium Nitrate Organic Compounds Elemental Carbon Ammonium Sulfate Other

Summer Constituent Contributions to Light Extinction

05

101520253035404550

Sacram

ento

Stockton

Modesto

Merced

Fresno Firs

tFresn

o MV

Fresno R

esSelm

aVisa

liaOild

aleBak

ersfiel

d Ca

Bakersf

ield R

esPe

rcen

t of S

easo

nal A

vera

ge

Ammonium Nitrate Organic Compounds Elemental Carbon Ammonium Sulfate Other

Water Contribution to Light Extinction

050

100150200250300350400450

Sacram

ento

Stockton

Modesto

Merced

Fresno Firs

tFresn

o MV

Fresno R

esSelm

aVisa

liaOild

aleBak

ersfiel

d Ca

Bakersf

ield R

esCa

lcul

ated

bex

t - D

ry b

ext (

Mm

-1)

Winter Spring Summer Fall

Water Contribution to Light Extinction

0102030405060708090

Sacram

ento

Stockton

Modesto

Merced

Fresno Firs

tFresn

o MV

Fresno R

esSelm

aVisa

liaOild

aleBak

ersfiel

d Ca

Bakersf

ield R

esPe

rcen

t of S

easo

nal A

vera

ge b

ext

Winter Spring Summer Fall

Summary• Previously developed light scattering efficiencies

under-predicted measured light scattering, butadjustment to f(RH) improved agreement

• Calculated light scattering agrees reasonably wellwith RR measurements at SJV sites

• Agreement is poor at Mojave Desert sites• Calculated total light extinction is highest during

winter and lowest during summer• NH4NO3 is the largest contributor at all sites during

winter and fall and at several sites during spring• Organic compounds are the highest contributor at

most sites during summer

Summary(continued)

• Water associated with ammonium nitrate andammonium sulfate accounts for about 60% to 80% ofcalculated light extinction during winter and about50% to 75% during fall