REGIONAL VISREGIONAL VISIBILITY IN THE UNITED STATES IBILITY IN THE UNITED STATES AND ITS VARIABILITY: AND ITS VARIABILITY: NATURAL AND NATURAL AND

TRANSBOUNDARYTRANSBOUNDARY POLLUTION POLLUTION INFLUENCES INFLUENCES

Rokjin Park

with support from EPRI, NASA, EPA (ICAP)

Rutgers University, November 04, 2005

NATIONAL PARKS AND OTHER NATURAL AREAS IN THE U.S.SUFFER SIGNIFICANT VISIBILITY DEGRADATION FROM

ANTHROPOGENIC AEROSOLS.

GlacierNationalPark

7.6 µgm-3 12.0 µgm-3

21.7 µgm-3 65.3 µgm-3

VISIBILITY METRICVISIBILITY METRIC

• VISUAL RANGE (km) - THE GREATEST DISTANCE AT WHICH AN OBSERVER CAN SEE A BLACK OBJECT VIEWED AGAINST BACKGROUND HORIZON - A quantitative measurement is subject to other conditions (Sun angle, light condition) than aerosol concentrations.

• EXTINCTION (bext, Mm-1) - THE AMOUNT OF LIGHT LOST AS IT TRAVELS OVER A MILLION METERS - Most useful for relating visibility directly to aerosol concentrations. - bext = 3f(RH)[(NH4)2SO4 + NH4NO3] + 4[OMC] + 10[EC] + [SOIL] + 0.6[CM] + 10 • DECIVIEWS (dv) – THE LOGARITHM OF THE EXTINCTION - dv = 10ln(bext/10) - A change in one dv is perceived to be the same under different conditions (clear and cloudy days).

U.S. EPA REGIONAL HAZE RULEU.S. EPA REGIONAL HAZE RULE

Because visibility is a logarithmic (sluggish) function of PM concentration,The 2004-2018 phase I implementation requires ~50% reduction in emissions, highly sensitive to specification of 2064 endpoint

visibility(deciviews)from

EPA [2001]

Anthropogenicemissions(illustrative)

• Federal class I areas (including national parks, other wilderness areas) to return to “natural visibility” conditions by 2064

• State Implementation Plans to be submitted by 2007 for linear improvement in visibility over the 2004-2018 period

EPA HAS PROPOSEDEPA HAS PROPOSED“DEFAULT ESTIMATED NATURAL PM CONCENTRATIONS” “DEFAULT ESTIMATED NATURAL PM CONCENTRATIONS”

FOR APPLICATION OF THE REGIONAL HAZE RULEFOR APPLICATION OF THE REGIONAL HAZE RULE

PM mass concentration (g m-3) Extinction coefficient (Mm-1)

These defaults are obtained by a simple extrapolation with measurements at clean remote sites [NAPAP report, 1990] and have a huge uncertainty. A better quantification of natural aerosol concentrations is crucial.

GlenCanyon, AZ

Clear day April 16, 2001: Asian dust!

Dust storms provide visible evidence of intercontinental transport of aerosols Dust storms provide visible evidence of intercontinental transport of aerosols and anthropogenic pollution is transported together with the dust

satellite data satellite data

[Heald et al., 2005]

TRANSBOUNDARY TRANSPORT COMPLICATES THE TRANSBOUNDARY TRANSPORT COMPLICATES THE DEFINITION OF “NATURAL VISIBILITY”DEFINITION OF “NATURAL VISIBILITY”

GEOS-ChemGEOS-Chem GLOBAL 3-D MODEL GLOBAL 3-D MODELOF ATMOSPHERIC TRANSPORT AND CHEMISTRYOF ATMOSPHERIC TRANSPORT AND CHEMISTRY

• Developed by Harvard Atmospheric Chemistry Modeling Group, used by 17 research groups in N. America and Europe; ~100 publications.

http://www-as.harvard.edu/chemistry/trop/geos

• driven by GEOS assimilated meteorological observations from NASA Global Modeling and Assimilation Office (GMAO); native resolution 1ox1o

• applied to simulations of ozone, aerosols (PM), CO2, methane, mercury, hydrogen,…

• Horizontal resolution 1ox1o to 4ox5o (user-selected), 48 levels in vertical

• Previous global evaluation of aerosol simulations in the United States, Europe, and East Asia by Park et al. [2003, 2004a, 2004b]; global evaluation by Martin et al. [2004].

• Conduct 1ox1o nested model simulations over North America with boundary condition from 4ox5o global model simulation.

2001 GEOS-Chem 12001 GEOS-Chem 1oox1x1oo NESTED SIMULATIONS NESTED SIMULATIONS

• Uses the coupled oxidant-aerosol version of GEOS-CHEM (version 7.02) with 1ox1o horizontal resolution over North America (140-40oW, 10-60oN) and 4ox5o horizontal resolution for the rest of the world.

• Includes weekday and weekend NEI99 anthropogenic emissions for NOx, CO, NMHC, and SO2 in the United States, EC and OC primary emissions from Bond et al. [2004] and Park et al. [JGR 2003], respectively.

• Include sulfur emissions in Canada and Mexico from EMEP and BRAVO emission estimates, respectively.

• Include a global ship SO2 emission [Corbett et al., 1999; Alexander et al., 2005].

• Includes a climatological biomass burning emission inventory with emission factors from Andreae and Merlet [2001].

• Includes a mechanistic simulation of secondary organic aerosols [Chung and Seinfeld, JGR 2002] coupled to oxidant chemistry

• Applies HNO3 and NH3 dry deposition to the mixed layer column.

Four simulations are conducted for 16 months starting from September 1, 2000:• baseline (emissions as described above)• natural (zero anthropogenic emissions worldwide)• background (zero anthropogenic emissions in the U.S.)• transpacific (zero anthropogenic emissions in North America)

ANNUAL MEAN SULFATE (2001): ANNUAL MEAN SULFATE (2001): GEOS-ChemGEOS-Chem (1 (1oox1x1oo)) vs. IMPROVE (135 sites) vs. IMPROVE (135 sites)

Highest concentrations in industrial Midwest (coal-fired power plants)

SULFATE AT SULFATE AT IMPROVE, CASTNET, IMPROVE, CASTNET,

NADP (deposition) NADP (deposition) SITES:SITES:

model (1model (1oox1x1oo) vs. ) vs. observed for different observed for different

seasonsseasons

High correlation in sulfate concentrations for different seasons (R2 = 0.83 - 0.92)

Low bias in summer and high bias in other seasons (Slope = 0.84 - 1.32)

ANNUAL MEAN AMMONIUM AND NITRATE (2001): ANNUAL MEAN AMMONIUM AND NITRATE (2001):

GEOS-Chem vs. CASTNET (79 sites)GEOS-Chem vs. CASTNET (79 sites)(no ammonium data at

IMPROVE sites)Highest concentrations in upper Midwest

The spatial distribution of ammonium and nitrate reflect the dominant ammonium nitrate formation in North America.

AMMONIUM AND AMMONIUM AND NITRATE AT NITRATE AT

CASTNET AND CASTNET AND IMPROVE SITES:IMPROVE SITES: model (1 model (1oox1x1oo) vs. ) vs.

observed for different observed for different seasonsseasons

High correlation for different seasons (R2 = 0.82-0.85)High bias for NH4

+ in fall:error in seasonal variation of livestock emissions

High bias for NO3-, esp. in

summer/fall, results from bias on [SO4

2-]-2[NH4+]

Ammonium Nitrate Nitrate

SEASONAL VARIATION OF NHSEASONAL VARIATION OF NH33 EMISSION EMISSION

Standard seasonal dependence of NH3 emissions used in GEOS-Chem produces a fall high bias in U.S., as shown previously in inverse modeling of NADP NH4

+ precipitation data by Gilliland et al. [JGR 2003]

[Park et al., 2004]

ANNUAL MEAN EC AND OC (2001):ANNUAL MEAN EC AND OC (2001):GEOS-Chem GEOS-Chem (1(1oox1x1oo)) vs. IMPROVE (135 sites) vs. IMPROVE (135 sites)

• High OC in southeast U.S.: vegetation• High EC/OC in west: fires

GEOS-Chem

IMPROVE

[µg m-3]

EC OC

EC AND OC AT EC AND OC AT IMPROVE SITES:IMPROVE SITES:

model vs. observed model vs. observed for different seasonsfor different seasons

No significant bias in OC with Park et al. [2003] emission butlarge scatter mostly fromSOA simulation dependent on preexisting primary organic aerosols [Chung and Seinfeld, 2002]

Low bias for EC indicates that Bond et al. [2004] EC emission is low in the U.S.

EC OC

VISIBILITY DEGRADATION STATISTICS IN THE U.S. (2001): VISIBILITY DEGRADATION STATISTICS IN THE U.S. (2001): IMPROVE vs. GEOS-CHEM (1IMPROVE vs. GEOS-CHEM (1oox1x1oo))

Visibility extinction (deciviews: dv = 10ln(bext/10) ) from sulfate, nitrate, EC, and OMC.

MEAN

STANDARDDEVIATION

R2 = 0.88

R2 = 0.63

CUMULATIVE CUMULATIVE DISTRIBUTION OF DISTRIBUTION OF

VISIBIILTY VISIBIILTY DEGRADATION IN DEGRADATION IN THE U.S. (2001): THE U.S. (2001):

IMPROVE vs. GEOS-IMPROVE vs. GEOS-CHEMCHEM

Model reproduces daily visibility degradation successfully at 53 out of 87 sites in the west and 24 out of 44 sites in the east.

Too much monoterpeneemission in northwest

Ammonium nitrate is too low in Southern California

Too much wet scavengingin southeast

Mexican sulfur emission in BRAVO inventory is lowerby 30% than Mexican NEI orglobal emission inventory.

CONTIGUOUS U.S. MAP CONTIGUOUS U.S. MAP (1(1oox1x1oo))

SIMULATED NATURAL AND BACKGROUND ANNUAL MEAN SIMULATED NATURAL AND BACKGROUND ANNUAL MEAN AEROSOL CONCENTRATIONS IN THE UNITED STATESAEROSOL CONCENTRATIONS IN THE UNITED STATES

SIMULATED NATURAL AND BACKGROUND ANNUAL MEAN SIMULATED NATURAL AND BACKGROUND ANNUAL MEAN AEROSOL CONCENTRATIONS (CONT.)AEROSOL CONCENTRATIONS (CONT.)

[mg m-3]

GEOS-CHEM (1ox1o)

with BC from 4ox5o

Ammonium

Sulfate

West East

Ammonium

Nitrate

West East

Elemental

Carbon

West East

Organic

Carbon Mass

West East

Background

Natural

Transboundary

pollution

Canada & Mexico

Rest of world

EPA natural defaults

0.50 0.86

0.17 0.17

0.33 0.71

0.22 0.54

0.11 0.15

0.12 0.23

0.06 0.12

0.01 0.01

0.05 0.11

0.04 0.09

0.01 0.02

0.10 0.10

0.04 0.03

0.03 0.01

0.01 0.03

0.01 0.02

0.01 0.01

0.02 0.02

0.68 0.77

0.58 0.65

0.10 0.12

0.08 0.10

0.02 0.02

0.47 1.40

Annual regional means averaged at IMPROVE sites from GEOS-Chem standard and sensitivity simulations

AEROSOL AEROSOL CONCENTRATIONS CONCENTRATIONS IN THE U.S.:IN THE U.S.:contributions from natural sources and transboundary pollutioncontributions from natural sources and transboundary pollution

• Transboundary pollution influences from Canada & Mexico are higher than those in Park et al. [2003, 2004], resulting in factor of 4 higher background concentration of ammonium sulfate than EPA default value.

MEAN PROFILES OF SOX, fine NO3-, BC

GEOS-CHEM chemical tracer model vs. TRACE-P observations

No significant model bias in SOx and fine NO3

- indicates a successful simulation of scavenging in Asian outflow.

Model underestimates BC observations by factor of 2; insufficient emissions [Bond et al., 2004] or excessive scavenging?

P3B DATA over NW Pacific (30 – 45oN, 120 – 140oE)

[Park et al., 2005]

BC IN THE ATMOSPHERE

PRIMARY EMISSION

Hydrophobic

oxidation

coating by sulfateor organics

CHEMICAL AGING

Hydrophilic

WET DEPOSITION

Most global models assume = 1 day for chemical conversion of hydrophobic to hydrophilic BC.

BC is operationally defined as the light-absorbing fraction of carbonaceous aerosols.

How much? How long ()?

EXPORT EFFICIENCY

)(][

][1)( z

CO

X

Rzf

XX

X = combustion-derived speciesRX = emission ratio (X/CO) Δ = enhancements relative to background

[Koike et al., 2003; Parrish et al, 2004]

)0(

)()(

X

XnormX f

zfzf

NORMALIZED EXPORT EFFICIENCY

INDEPENDENT OF EMISSION RATIO, R

BC emissions over East Asia are highly uncertain [Carmichael et al, 2003].

We use the TRACE-P P-3B data north of 30oN for which China provided a common source region.

OBSERVED EXPORT EFFICIENCYBC vs SOX (≡SO2(g)+SO4

2-) and HNO3T (≡HNO3(g)+NO3

-)

BC AEROSOLS ARE SIGNIFICANTLY SOLUBLE BUT NOT AS MUCH AS SULFATE OR NITRATE.

Export efficiency Normalized export efficiency

[Park et al., 2005]

BC NORMALIZED EXPORT EFFICIENCY IN ASIAN OUTFLOW (GEOS-CHEM vs TRACE-P )

Simulation with = 1±1 days for BC scavenging provides the best fit to the TRACE-P observations.

[Park et al., 2005]

AN EXAMPLE OF TRANSPACIFIC TRANSPORT OF ASIAN AEROSOL POLLUTION AS SEEN BY MODIS

April 25, 2001

April 26, 2001

April 27, 2001

[Heald et al., 2005]

ASIAN TRANSPORT EVENT: MAY 19, 2001 ASIAN TRANSPORT EVENT: MAY 19, 2001

IMPROVE SO42- surface concentrations

GEOS-CHEM Asian anthropogenic SO4

2- surface concentrations

This was the largest “Asian” event simulated by GEOS-CHEM. Concentrations ofsulfate due to Asian sources at sites on the northern west coast exceeded 1 µg/m3.

ASIAN POLLUTION CONTRIBUTION TO ANNUALASIAN POLLUTION CONTRIBUTION TO ANNUAL SULFATE SULFATE CONCENTRATIONSCONCENTRATIONS IN SURFACE AIR IN SURFACE AIR (IMPROVE(IMPROVE SITES SITES))

IMPROVE SO42- GEOS-CHEM SO4

2-

ASIAN SO42- (GEOS-CHEM) % ASIAN CONTRIBUTION

R2: 0.88Slope: 1.1

ASIAN SO42- CONTIRUBTIONS ARE COMPARABLE TO EPA NATURAL VALUES.

END POINT VISIBILITY DEGRADATION FOR WORST END POINT VISIBILITY DEGRADATION FOR WORST 20% DAYS IN THE UNITED STATES20% DAYS IN THE UNITED STATES

• The EPA default endpoint visibility shows a simple separation between the western and the eastern United States for which we find little basis. • Our natural visibility endpoint has a considerable spatial variation and in general lower than the EPA default in the east. • Background endpoint visibility is higher than natural visibility and is more spatially variable due to transboundary pollution influences.

IMPLICATIONS FOR EMISSION REDUCTIONS IN PHASE 1 (2004-2018)IMPLICATIONS FOR EMISSION REDUCTIONS IN PHASE 1 (2004-2018) IMPLEMENTATION OF REGIONAL HAZE RULE IMPLEMENTATION OF REGIONAL HAZE RULE

Illustrative calculation for NW IMPROVE sites based on 20% worst visibility days statistics, assuming linear relationship between emissions and PM concentrations, and assuming constant anthropogenic sources from foreign countries between now and 2064

Desired trend in visibility

Required % decrease of U.S. anthropogenic emissions

Phase 1

53%

28%

DECIVIEW

BASELINE (2001) 14

BACKGROUND 10.6

NATURAL

THIS WORK 8.5

EPA DEFAULT 7.3

VISIBILITY DEGRADATION

ON 20% WORST VISIBILITY

DAYS AT NORTHWESTERN

IMPROVE SITES.

WHERE ARE ASIAN EMISSIONS HEADED?WHERE ARE ASIAN EMISSIONS HEADED?It’s anybody’s guessIt’s anybody’s guess

Past trends and future projections of Chinese SO2 emissions [Streets et al., 2002]