REGIONAL VISIBILITY IN THE UNITED STATES AND ITS VARIABILITY: NATURAL AND TRANSBOUNDARY POLLUTION 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. Glacier National Park 7.6 µgm µgm µgm µgm -3

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 (b ext, Mm -1 ) - THE AMOUNT OF LIGHT LOST AS IT TRAVELS OVER A MILLION METERS - Most useful for relating visibility directly to aerosol concentrations. - b ext = 3f(RH)[(NH 4 ) 2 SO 4 + NH 4 NO 3 ] + 4[OMC] + 10[EC] + [SOIL] + 0.6[CM] + 10 DECIVIEWS (dv) – THE LOGARITHM OF THE EXTINCTION - dv = 10ln(b ext /10) - A change in one dv is perceived to be the same under different conditions (clear and cloudy days).

U.S. EPA REGIONAL HAZE RULE Because visibility is a logarithmic (sluggish) function of PM concentration, The phase I implementation requires ~50% reduction in emissions, highly sensitive to specification of 2064 endpoint visibility (deciviews) from EPA [2001] Anthropogenic emissions (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 period

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 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.

Glen Canyon, AZ Clear dayApril 16, 2001: Asian dust! Dust storms provide visible evidence of intercontinental transport of aerosols and anthropogenic pollution is transported together with the dust satellite data [Heald et al., 2005] TRANSBOUNDARY TRANSPORT COMPLICATES THE DEFINITION OF “NATURAL VISIBILITY”

GEOS-Chem GLOBAL 3-D MODEL OF ATMOSPHERIC TRANSPORT AND CHEMISTRY Developed by Harvard Atmospheric Chemistry Modeling Group, used by 17 research groups in N. America and Europe; ~100 publications. driven by GEOS assimilated meteorological observations from NASA Global Modeling and Assimilation Office (GMAO); native resolution 1 o x1 o applied to simulations of ozone, aerosols (PM), CO 2, methane, mercury, hydrogen,… Horizontal resolution 1 o x1 o to 4 o x5 o (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 1 o x1 o nested model simulations over North America with boundary condition from 4 o x5 o global model simulation.

2001 GEOS-Chem 1 o x1 o NESTED SIMULATIONS Uses the coupled oxidant-aerosol version of GEOS-CHEM (version 7.02) with 1 o x1 o horizontal resolution over North America ( o W, o N) and 4 o x5 o horizontal resolution for the rest of the world. Includes weekday and weekend NEI99 anthropogenic emissions for NO x, CO, NMHC, and SO 2 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 SO 2 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 HNO 3 and NH 3 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 (1 o x1 o ) vs. IMPROVE (135 sites) Highest concentrations in industrial Midwest (coal-fired power plants)

SULFATE AT IMPROVE, CASTNET, NADP (deposition) SITES: model (1 o x1 o ) vs. observed for different seasons High correlation in sulfate concentrations for different seasons (R 2 = ) Low bias in summer and high bias in other seasons (Slope = )

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.

AMMONIUM AND NITRATE AT CASTNET AND IMPROVE SITES: model (1 o x1 o ) vs. observed for different seasons High correlation for different seasons (R 2 = ) High bias for NH 4 + in fall: error in seasonal variation of livestock emissions High bias for NO 3 -, esp. in summer/fall, results from bias on [SO 4 2- ]-2[NH 4 + ] Ammonium Nitrate Nitrate

SEASONAL VARIATION OF NH 3 EMISSION Standard seasonal dependence of NH 3 emissions used in GEOS-Chem produces a fall high bias in U.S., as shown previously in inverse modeling of NADP NH 4 + precipitation data by Gilliland et al. [JGR 2003] [Park et al., 2004]

ANNUAL MEAN EC AND OC (2001): GEOS-Chem (1 o x1 o ) 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 IMPROVE SITES: model vs. observed for different seasons No significant bias in OC with Park et al. [2003] emission but large scatter mostly from SOA 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. ECOC

VISIBILITY DEGRADATION STATISTICS IN THE U.S. (2001): IMPROVE vs. GEOS-CHEM (1 o x1 o ) Visibility extinction (deciviews: dv = 10ln(b ext /10) ) from sulfate, nitrate, EC, and OMC. MEAN STANDARD DEVIATION R 2 = 0.88 R 2 = 0.63

CUMULATIVE DISTRIBUTION OF VISIBIILTY DEGRADATION IN THE U.S. (2001): IMPROVE vs. GEOS- CHEM 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 monoterpene emission in northwest Ammonium nitrate is too low in Southern California Too much wet scavenging in southeast Mexican sulfur emission in BRAVO inventory is lower by 30% than Mexican NEI or global emission inventory.

CONTIGUOUS U.S. MAP (1 o x1 o )

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

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

[m g m -3 ] GEOS-CHEM (1 o x1 o ) with BC from 4 o x5 o 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 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.

MEAN PROFILES OF SO X, fine NO 3 -, BC GEOS-CHEM chemical tracer model vs. TRACE-P observations No significant model bias in SO x and fine NO 3 - 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 – 45 o N, 120 – 140 o E) [Park et al., 2005]

BC IN THE ATMOSPHERE PRIMARY EMISSION Hydrophobic oxidation coating by sulfate or 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 X = combustion-derived species R X = emission ratio (X/CO) Δ = enhancements relative to background [Koike et al., 2003; Parrish et al, 2004] 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 30 o N for which China provided a common source region.

OBSERVED EXPORT EFFICIENCY BC vs SO X (≡SO 2 (g)+SO 4 2- ) and HNO 3 T (≡HNO 3 (g)+NO 3 - ) 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 IMPROVE SO 4 2- surface concentrations GEOS-CHEM Asian anthropogenic SO 4 2- surface concentrations This was the largest “Asian” event simulated by GEOS-CHEM. Concentrations of sulfate due to Asian sources at sites on the northern west coast exceeded 1 µg/m 3.

ASIAN POLLUTION CONTRIBUTION TO ANNUAL SULFATE CONCENTRATIONS IN SURFACE AIR (IMPROVE SITES) IMPROVE SO 4 2- GEOS-CHEM SO 4 2- ASIAN SO 4 2- (GEOS-CHEM) % ASIAN CONTRIBUTION R 2 : 0.88 Slope: 1.1 ASIAN SO 4 2- CONTIRUBTIONS ARE COMPARABLE TO EPA NATURAL VALUES.

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 ( ) 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? It’s anybody’s guess Past trends and future projections of Chinese SO 2 emissions [Streets et al., 2002]