NATURAL AND TRANSBOUNDARYNATURAL AND TRANSBOUNDARY POLLUTION POLLUTION INFLUENCES ON INFLUENCES ON AEROSOL CONCENTRATIONS AND AEROSOL CONCENTRATIONS AND VISIBILITY DEGRADATION IN THE UNITED STATESVISIBILITY DEGRADATION IN THE UNITED STATES

Rokjin J. Park, Daniel J. Jacob, Colette L. Heald, T. Duncan

Fairlie, Robert M. Yantosca

AWMA, October 29, 2004

with support from EPRI, NASA, EPA (ICAP)

OBJECTIVES and APPROACHOBJECTIVES and APPROACH• Determine present-day natural PM concentrations in the U.S., compared to

EPA “default” values.• Determine the contributions from foreign anthropogenic emissions (Canada,

Mexico, Asia) to visibility degradation in the U.S.• Determine the pervasiveness of natural fires and dust events, particularly

from outside the U.S, in decreasing natural visibility in the U.S.

Start from best a priori estimates of natural

and anthropogenic PM sources

Conduct global oxidant-PM simulation with

GEOS-CHEM chemical tracer model

Evaluate model with aerosol data from IMPROVE, CASTNET, other networks

Conduct sensitivity simulationsAssessment of transboundary

pollution influences

Assessment of EPA “default estimated

natural PM concentrations”

Improved emission estimates

g m-3] Ammonium

Sulfate

West East

Ammonium

Nitrate

West East

Elemental

Carbon

West East

Organic

Carbon Mass

West East

Baseline (2001)

Background

Natural

Transboundary

pollution

Canada & Mexico

Asia

EPA natural defaults

1.52 4.11

0.43 0.38

0.11 0.11

0.28 0.26

0.15 0.14

0.13 0.12

0.12 0.23

1.53 3.26

0.27 0.37

0.03 0.03

0.18 0.23

0.20 0.25

-0.02 -0.02

0.10 0.10

0.27 0.66

0.08 0.06

0.06 0.04

0.02 0.02

0.02 0.02

<0.01 <0.01

0.02 0.02

1.77 3.07

1.30 1.22

1.25 1.17

0.05 0.05

0.04 0.04

0.01 <0.01

0.47 1.40

Annual regional means 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

• We find that EPA default natural concentrations are too low by factors of 2-3 except for OC in eastern U.S. – quantifying fire influences is critical• Transboundary pollution influence from Asia is comparable in magnitude to that from Canada + Mexico [Park et al., 2003, 2004]

IMPLICATIONS FOR 2004-2018 IMPLEMENTATION IMPLICATIONS FOR 2004-2018 IMPLEMENTATION OF REGIONAL HAZE RULEOF REGIONAL HAZE RULE

Illustrative calculation for mean western U.S. conditions, assuming linear relationship between emissions and PM concentrations, and assuming zero trend in anthropogenic sources from foreign countries between now and 2064

Desired trend in visibility

Required % decrease of U.S. anthropogenic emissions

Phase 1

29%

44%

Park et al. [2004]

VISIBILITY DEGRADATION STATISTICS IN THE VISIBILITY DEGRADATION STATISTICS IN THE UNITED STATES (2001): IMPROVE vs. GEOS-CHEMUNITED STATES (2001): IMPROVE vs. GEOS-CHEM

Visibility decrease (deciviews: dv = 10ln(bext/10) )from sulfate, nitrate, and carbonaceous aerosols

R.J. Park (Harvard)

FREQUENCY DISTRIBUTION OF DAILY VISIBILITY DEGRADATION (2001): FREQUENCY DISTRIBUTION OF DAILY VISIBILITY DEGRADATION (2001): IMPROVE SITE OBSERVATIONS vs. MODELIMPROVE SITE OBSERVATIONS vs. MODEL

IMPROVE (EAST)

MEAN > 18 STD > 5

MEAN > 18 STD < 5

IMPROVE vs. MODELREGION 1

REGION 2

MEAN < 9 STD < 3.5

REGION 4IMPROVE (WEST)

Successful simulation of low end of pdf increases confidence in ability of modelto describe natural (and transboundary?) signatures

R.J. Park (Harvard)

DUST STORMS PROVIDE VISIBLE EVIDENCEDUST STORMS PROVIDE VISIBLE EVIDENCEOF INTERCONTINENTAL TRANSPORT OF AEROSOLS OF INTERCONTINENTAL TRANSPORT OF AEROSOLS

GlenCanyon, AZ

Clear day April 16, 2001: Asian dust!

…and anthropogenic pollution is transported together with the dust

Colette Heald et al. (Harvard)

satellite data satellite data

ASIAN PM POLLUTION INFLUENCE OVER WESTERN U.S. ASIAN PM POLLUTION INFLUENCE OVER WESTERN U.S.

-*- AERONET__GEOS-CHEM __ Asian SO4+NH4+Nit __ Asian Dust

Spring 2001

What about in surface air? Observations at clean western U.S. sites indicate Asian sulfate influence up to 2.2 g m-3 (24-h average) [Jaffe et al., 2003]

AERONET aerosol optical depth (AOD) measurements at Missoula, MT

Colette Heald et al. (Harvard)

AO

D

GEOS-CHEM SIMULATION OF TRACE-P OBSERVATIONSGEOS-CHEM SIMULATION OF TRACE-P OBSERVATIONS

BC underestimated by factor of 2 because emissions [Bond et al.] are too low

Park et al. [2004b]

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

Scavenging from Asian outflow is 80-90% efficient for sulfate and BC, ~100% for nitrate

Black carbon(BC)

ASIAN POLLUTION INFLUENCES ON SOASIAN POLLUTION INFLUENCES ON SO442-2-/NO/NO33

--/NH/NH44++ PM PM

Annual means as determined from a GEOS-CHEM 2001 sensitivity simulation with Asian anthropogenic sources shut off

SO42-

NO3-

NH4+

g m-3

Mean Asian pollution enhancements for U.S. surface aerosols are greatest for sulfate (0.1 μg m-3) and less for other aerosols (scavenging during outflow)

SEASONAL VARIATION OF ASIAN POLLUTION INFLUENCES SEASONAL VARIATION OF ASIAN POLLUTION INFLUENCES ON ON SOSO44

2-2-/NO/NO33--/NH/NH44

++ PM PM IN THE UNITED STATES IN THE UNITED STATES

The transpacific transport of Asian pollution is largest during spring andminimum in summer.

Monthly mean SO42--NO3

--NH4+ enhancements due to Asian pollution

RELATIVE HUMIDITY WEIGHTING FACTORS, RELATIVE HUMIDITY WEIGHTING FACTORS, ff(RH): (RH): IMPROVE vs. GEOS-CHEM (2001)IMPROVE vs. GEOS-CHEM (2001)

Use ISORROPIA + MIE computation with 3-h SO42--NO3

--NH4+ , RH

Aerosol acidity results in higher f(RH) than recommended values especiallyat RH greater than 60%.

[NH4+] /

([SO42-]+[NO3

-])

WEST EAST

SEASONAL AND SPATIAL DISTRIBUTION OF BACKGROUD SEASONAL AND SPATIAL DISTRIBUTION OF BACKGROUD AEROSOL ACIDITY IN THE UNITED STATES AEROSOL ACIDITY IN THE UNITED STATES

Seasonal means as determined from a GEOS-CHEM 2001 sensitivity simulation with US anthropogenic sources shut off

DJF MAM

JJA SON

[NH4+] /

(2[SO42-]+[NO3

-])

Background aerosols are not fully neutralized in the west except in summer implying higher background visibility endpoint?

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]