1. BACKGROUND AEROSOL CONCENTRATIONS AND VISIBILITY DEGRADATION IN THE UNITED STATES Rokjin Park Motivated by EPA Regional Haze Rule Quantifying uncontrollable transboundary pollution transport is crucial [Park et al., 2003; 2004] 2 nd GEOS-CHEM User’s meeting, April 4, 2005

2. SIMULATED BASELINE AND BACKGROUND ANNUAL MEAN SULFATE AND NITRATE CONCENTRATIONS (2001) BACKGROUND CONC.BASELINE CONC. SO 4 2- NO 3 - µg m -3

3. SIMULATED ANNUAL MEAN AEROSOL CONCENTRATIONS (2001): OMC, EC, SOIL DUST, SEA SALT OMC EC SEA SALT SOIL DUST µg m -3

4. VISIBILITY DEGRADATION STATISTICS IN THE U.S. (2001): IMPROVE vs. GEOS-CHEM (1 o x1 o ) Visibility degradation (deciviews): dv = 10ln(b ext /10) Aerosol extinction (b ext ) from sulfate, nitrate, and carbonaceous aerosols: b ext = 3f(rh)[sulfate+nitrate] + 4[OMC] + 10[EC] + [soil] + 0.6[CM] + 10.

5. VISIBILITY DEGRADATION BY SULFATE IN THE SOUTH ATLANTIC AND ITS VARIABILITY: IMPROVE vs. GEOS-CHEM

6. GEOS-3 1 o x1 o PRECIPITATION IN JJA (2001) TOTAL PRECIPITATION CONVECTIVE PRECIPITATION AEROSOL WET SCAVENGING IS TOO MUCH IN SUMMER? PRECIPITATION OVER THE GULF OF MEXICO AND THE SOUTH EASTERN UNITED STATES IS MOSTLY CONVECTIVE PRECIPITATION DURING SUMMER. mm d -1

7. PRECIPITATION IN SUMMER (2001): GMAO VS. NCEP / GPCP

8. VISIBILITY DEGRADATION BY SULFATE IN THE S. WESTERN U.S. AND ITS VARIABILITY: IMPROVE vs. GEOS-CHEM

9. Gg S yr -1 GEOS-CHEM: 1.9 Tg S yr -1 BRAVO: 1.3 Tg S yr -1 Courtesy of Dr. Soontae Kim at U. Houston MEXICAN SULFUR EMISSIONS (1 o x1 o ): GEOS-CHEM (2001) VS. BRAVO (1999)

10. VISIBILITY DEGRADATION STATISTICS IN THE U.S. EAST(2001): IMPROVE vs. GEOS-CHEM (1 o x1 o ) at selected IMPROVE sites in the east (>95 o W) FREQUENCY DISTRIBUTION OF DAILY VISIBILITY IMPROVE MODEL IMPROVE MODEL Visibility extinction (deciviews: dv = 10ln(b ext /10) ) from sulfate, nitrate, and carbonaceous aerosols + observed contribution from soil dust and coarse mass (2001)

11. SIMULATED NATURAL AND BACKGROUND VISIBILITY DEGRADATION STATISTICS IN THE U.S. EAST DEFINE NATURAL AND BACKGROUND CONCENTRATIONS FROM SENSITIVITY MODEL SIMULATIONS WITH NO GLOBAL AND U.S. ANTHROPOGENIC EMISSIONS, RESPECTIVELY. FREQUENCY DISTRIBUTION OF DAILY VISIBILITY BACKGROUND NATURAL Uncontrollable anthropogenic contribution from outside U.S. NO U.S. NO GLOBE NO NA

12. at selected IMPROVE sites in the west (<95 o W) FREQUENCY DISTRIBUTION OF DAILY VISIBILITY IMPROVE MODEL VISIBILITY DEGRADATION STATISTICS IN THE U.S. NORTHWEST(2001): IMPROVE vs. GEOS-CHEM (1 o x1 o ) Successful simulation of low end of pdf increases confidence in ability of model to describe natural (and transboundary?) signatures IMPROVE MODEL

13. SIMULATED NATURAL AND BACKGROUND VISIBILITY DEGRADATION STATISTICS IN THE U.S. WEST FREQUENCY DISTRIBUTION OF DAILY VISIBILITY BACKGROUND NATURAL NO U.S. NO GLOBE NO NA