presents:/slides/greg/psat_11-17-03.ppt effects of sectional pm distribution on pm modeling in the...

Presents:/slides/greg/PSAT_11-17-03.ppt

Effects of Sectional PM Distribution on PM Modeling in the Western US

Ralph Morris and Bonyoung Koo

ENVIRON International Corporation

Novato, CA([email protected])

National RPO Modeling Meeting

Denver, Colorado

May 24-25, 2004


Outline

• Introduction• Previous Results in SoCal• WRAP 1996 Western US Modeling• Conclusions


CAMx4+ PM Treatment• PM Size Distribution

> Mechanism 4 (M4) 2-section (fine/coarse)> Sectional (N-Section, N=10, 4,…)

• Allows side-by-side comparisons of Sectional versus fine/coarse PM size distribution treatment in same platform

• Aqueous-Phase Chemistry> RADM Bulk Module> Variable Size Resolution Module (VSRM)

• Allows analysis of the effects of treating PM size distribution in aqueous-phase chemistry (buffering issues)

• Aerosol Thermodynamics> ISORROPIA

• PM Size Distribution> Equilibrium, Dynamic, Hybrid

• Secondary Organic Aerosol> SOAP


Sectional vs. Fine/Coarse Comparisons in Southern California (presented previously)

• South Coast Air Basin (SoCAB) of Southern California• October 17-19, 1995 PTEP episode

> High NO3 Episode• Analyze Effect of PM Size Resolution in VSRM

Aqueous-phase Chemistry> CMU 1-section Bulk Module> CMU Variable Size Resolution Model (VSRM)

• Analyze Effects of 10-Section Versus 2-Section (Fine/Coarse) Representation on PM Size Resolution> M4 = Mechanism 4 Fine/Coarse> EQUI = 10-Section PM Representation


VSRM (Multi-Section) vs. Bulk Aqueous ChemistryPercent Increase in Sulfate (%)

By second day, VRSM estimates ~15-30% more sulfate across the SoCAB with > 50% increase offshore and around Long Beach


VSRM (Multi-Section) vs. Bulk Aqueous Chemistry

PM10 Sulfate - Long Beach - Oct. 18, 1995

0

5

10

15

20

25

30

1 6 11 16 21

Time (hr)

Sulfa

te (

m g/m

3) VSRM

Bulk

No Aqueous-PhaseChem.

> 6 mg/m3 difference

> 16% difference in daily avg

PM10 Sulfate - (18,15) - Oct. 18, 1995

0

5

10

15

20

1 6 11 16 21

Time (hr)Su

lfate

(m g

/m3

) > 10 mg/m3 difference

> 31% difference in daily avg

VRSM can form significantly more sulfate than the bulk 1-section aqueous-phase chemistry module


24-Hour Nitrate (g/m3)

October 18, 1995

• M4 peak NO3 83 g/m3

• EQUI peak NO3 54 g/m3

• Observed NO3 peak at Riverside ~40 g/m3

• Differences due to assuming all nitrate is fine vs. PM nitrate represented by 10 size sections (EQUI)

M4

EQUI


Differences in 24-Hour Nitrate (g/m3)

October 18, 1995

• M4 peak NO3 83 g/m3

• EQUI peak NO3 54 g/m3

• EQUI 10-Section grows PM NO3 into coarser sections where it dry deposits faster than M4 NO3 that is assumed to be fine

• Result is less NO3 in downwind Riverside area that agrees better with observations

M4

M4 - EQUI

0

10

20

30

40

50

60

70

80

90

0.01 0.1 1 10

M4

EQUI

MADM

RADM/EQ

Diameter [mm]

dM

/dL

og

(D)

[mg

/m3]


WRAP/CRC Modeling Analysis

• 1996 36 km Western US> (Section 309 Database)

• Evaluate Four Models:> CMAQ V4.3> REMSAD V7> CAMx_M4 – Mechanism 4 Fine/Coarse> CAMx_4sec – 4-Sections, Section 4 is Coarse

• Use same emissions, IC/BC, vertical layers, etc.• No Sea Salt or Explicit Calcium Emissions in WRAP

1996 Database• How much SO4 and NO3 in Coarse Model?


Example SO4 Model Performance

-60

-40

-20

0

20

40

60

CMAQ REMSAD M4 4sec

0102030405060708090

CMAQ REMSAD M4 4sec

Yellow = 1996 Annual

Blue = January 1996

Red = July 1996

Fractional Bias Fractional Gross Error

Winter overestimation compensates for summer underestimation results in annual bias < 10%


Average 1996 PM Concentrations Across IMPROVE Monitors (Section 4 = Coarse)

0

0.5

1

1.5

2

1 2 3 4

Sulfate

Nitrate

Ammonium

Organics

Others

PM

co

mp

on

en

t (m g

/m3 )

Size section


Conclusions Western US Sectional vs. Fine Coarse PM Distribution Representation

• Sectional 1996 Annual Modeling (4-Sections) Estimates that 10% of the Sulfate and 5% of the Nitrate is in the Coarse Mode (PM2.5-10)

• SoCal Analysis Suggests:> Sectional Approach Affects Aqueous-Phase Chemistry> Biggest Effect is on Dry Deposition Rates

• Several Caveats Should be Mentioned:> Sea Salt was not included in the WRAP 1996 database

which is known to form coarse Sodium Nitrate• Important at Coastal Sites and Desert Areas

> Other Soil buffering compounds (e.g., Calcium) were not explicitly treated

presents:/slides/greg/psat_11-17-03.ppt effects of sectional pm distribution on pm modeling in the...

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