NATURAL AND TRANSBOUNDARY POLLUTION INFLUENCES ON REGIONAL VISIBILITY STATISTICS IN THE UNITED STAT

ES

with support from EPRI, NASA

Dalhousie University, May 19, 2006

Rokjin Park

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

ATMOSPHERIC PARTICULATE MATTER (AEROSOLS)

Soil dustSea salt

Aerosol: dispersed condensed matter suspended in a gasSize range: 0.001 m (molecular cluster) to 100 m (small raindrop)

SO2, NOx,NH3, VOCs

Most important components of the atmospheric aerosol:-Sulfate- nitrate-ammonium-Organic carbon (OC), elemental carbon (EC)-Soil dust-Sea salt

Lifetime ≈ 4 – 6 days

VISIBILITY 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).

[Pitchford and Malm, 1994]

U.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

U.S. EPA HAS PROPOSED“DEFAULT ESTIMATED NATURAL PM CONCENTRATIONS”

FOR APPLICATION OF THE REGIONAL HAZE RULE

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

These defaults are based on measurements at clean remote sites [NAPAP report, 1990]. A better quantification of natural aerosol concentrations is crucial.

OBJECTIVE #1

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 DEFINITION OF “NATURAL VISIBILITY”

OBJECTIVE #2

GEOS-Chem GLOBAL 3-D MODELOF 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.

SULFATE-NITRATE-AMMONIUM AEROSOL

SO2

DMS

NH3

Ocean

OH, NO3

Volcanoes Fossil fuel Domesticated Fertilizers Fossil Fuel Biomass Animals burning

NOx

LightningHNO3

OHOH

H2SO4

H2O2 (aq), O3 (aq)

SO42-

NH4NO3(NH4)2SO4

NH4+

SO42-

NO3-

H2OAqueous phasef(T, RH, C)

Aerosol thermodynamic calculations using RPMARES or ISORROPIA

Solid

(N2O5)

pH = 4.5

ORGANIC CARBON AEROSOL

Oxidation by OH, O3, NO3

Direct Emission

Fossil Fuel Biomass Vegetationcombustion burning

Biogenic VOCs (Monoterpenes)

SECONDARY ORGANIC AEROSOL (SOA) SIMULATION [Chung and Seinfeld, 2002]

VOCi + OXIDANTj i,jP1i,j + i,jP2i,j

Parameters (’s K’s) from smog chamber studies

Ai,j

GGi,ji,j

Pi,jEquilibrium (Komi,j) also f(POA)

ReactiveOrganicGases

Condense on pre-existing aerosol

AromaticsIsoprene as a SOA source? [Claeys et al., 2004; Matsunaga et al., 2005; Lim et al., 2005; Kroll et al., 2005; Henze and Seinfeld., 2006; van Donkelaar et al., in review]

BLACK CARBON 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 ()?

2001 GEOS-Chem 1ox1o 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 fr

om Andreae and Merlet [2001]. • Includes a mechanistic simulation of secondary organic aerosols [Chung and Seinfel

d, 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): GEOS-Chem (1ox1o) vs. IMPROVE (135 sites)

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

SULFATE AT IMPROVE, CASTNET,

NADP (deposition) SITES:

model (1ox1o) vs. observed for different

seasons

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): 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.

NH4+ NO3

-

AMMONIUM AND NITRATE AT

CASTNET AND IMPROVE SITES: model (1ox1o) vs.

observed for different seasons

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

ANNUAL MEAN EC AND OC (2001):GEOS-Chem (1ox1o) vs. IMPROVE (135 sites)

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

GEOS-Chem

IMPROVE

[µg m-3]

EC AND OC AT IMPROVE SITES:

model vs. observed for 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 could be low in the U.S.

EC OC

VISIBILITY DEGRADATION STATISTICS IN THE U.S. (2001): IMPROVE vs. GEOS-CHEM (1ox1o)

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

R2 = 0.88

R2 = 0.63

CUMULATIVE DISTRIBUTION OF

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

IMPROVE (black) vs. GEOS-CHEM (red)

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.

Dec

ivie

ws

110 E 120 E 130 E 140 E 150 E 160 E

Longitude

0 N

10 N

20 N

30 N

40 N

50 N

Lat

itu

de

DC-8 FlightsP-3B Flights

GEOS-CHEM SIMULATION OF TRACE-P OBSERVATIONSScavenging from Asian outflow is 80-90% efficient for sulfate and BC, ~100% for nitrate

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

Black carbon(BC)

TRACE-P (Mar-Apr, 2001) flight tracks for DC-8, P3-B aircraft

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

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]

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

[Park et al., 2005]

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

IMPLICATION FOR CLIMATEBC BURDEN & ARCTIC DEPOSITION FLUX

BC lifetime is 5.8 ± 1.8 days, 50% longer than that of sulfate, global burden is 0.11 ± 0.03 Tg using Bond et al. [2004] inventory, and resulting decrease in Arctic snow albedo = 3.2 ± 2.5% with = 1 ± 1 days from the TRACE-P constraints [Park et al., 2005]

CONTIGUOUS U.S. MAP (1ox1o):background simulations with shutting off U.S anthropogenic emissions

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

SIMULATED NATURAL AND BACKGROUND ANNUAL MEAN 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 0.53

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 CONCENTRATIONS IN THE U.S.:contributions 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.

END POINT VISIBILITY DEGRADATION FOR WORST 20% 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) 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.

PROJECTED SOx EMISSIONS IN ASIA

Increasing SOx emissions from Asia will degrade North American air quality and present a further barrier to attainment of domestic air quality regulations

in the United States (eg. EPA Haze Rule)

courtesy: David Streets

One projection suggests that

emissions of SOx will more than

double in China between

1995-2020

[Streets & Waldhoff, 2000]