1 The Asian Aerosol Contribution to North American PM Pollution: Recognizing Asian Transport Composition and Concentration Modeling Regional Aerosol Burdens Richard “Tony” VanCuren California Air Resources Board ICAP October 22, 2004

2 MOPITT CO March-Dec. 2000

3 The April 1998 Asian Dust Storms: a Natural Experiment Image after Husar, 2000 VanCuren & Cahill, 2002

4 Asian Dust Frequency (% of days by month ) Northeast Pacific Basin VanCuren & Cahill, 2002

5 Comparative Frequency and Concentration Asian vs. African Dust in Eastern North America FREQUENCY CONCENTRATION | VanCuren & Cahill, 2002

6 Composition of the Whole Asian Plume: “Minimum Concentration” Hypothesis: Lemma: Asian pollutants in West are broadly distributed, and ~ equal; local pollutants are variable. Implications: Mean concentration = mean Asian + mean local concentrations. Lowest means imply least local pollutants - CRLA & LAVO. Staged Analysis (Crater Lake & Lassen): Selected Asian Days: First Approximation - composition when Asian dust dominates and no local fires (low OC/S). All Asian Days: Aerosol composition for all days with Asian Dust - recognize local fire contribution. All Days: Aerosol composition for all days in transport season (March - October) - recognize local sources.

7 Generalizing - known events to all days

8 Regression-Derived Source & Composition Breakdown for Crater Lake / Mt. Lassen Aerosol

9 What is the temporal structure of Asian transport? “SPRING” research model: –Based on data from Mauna Loa –Subsequent field studies have focused on spring sampling “EPISODIC” research model: –A priori assumption based on experience with Asian “Yellow Sand” dust storms –Bolstered by “mass = event” logic in studying Asian outflow gas and aerosol chemistry and transport meteorology –Reinforced by conservative receptor analyses (e.g. cluster analysis of 1998 dust storm) An unbiased measurement: –Continuous sampling during ITCT-2K2

10 ITCT-2K2 Aerosol Measurement Sites

11 Trinidad Head Aerosol Time Series - ITCT-2K2 4/21 - 4/24 VanCuren et al., 2004

12 Trinity Alps Aerosol Time Series - ITCT-2K2 4/21 - 4/24 VanCuren et al., 2004

13 Mt. Lassen Aerosol Time Series - ITCT-2K2 4/21 - 4/24 VanCuren et al., 2004

14 Concordant Montane Aerosol: Concordant Montane Aerosol: Single dominant aerosol Asian origin confirmed by soil element profiles Concentration varies but continuously present VanCuren et al., 2004

15 Asian aerosol persists even after rain VanCuren et al., 2004 Trinity Max Lassen Max

16 Observational Findings Asian Continental Aerosol Plume is persistent over western North America; detectable Alaska to Virgin Islands Average concentration is about 5  g/m 3 PM10 Mass median diameter is 2-3  m Average PM2.5 concentration is about 3  g/m 3 1/2 of coarse, 3/4 of fines at CRLA & LAVO Approximately ¼ of the new annual California AAQS for PM10 and PM2.5 Approximately 1/10 of the new Federal annual PM10 NAAQS; 1/5 of the annual PM2.5 NAAQS Asian aerosols are the regional “clean” background in much of North America

17 Modeling Western U.S. PM Air Quality Failure Modes: Estimation Error and Process Error YOSE SO 4 PINN SO 4 Expected uncertainty in regional models. Systematic divergence between model and reality.

18 Process error may be widespread: Colorado Plateau fine soil GRBABRCAMOZI BRCAGRCACANY WEMIMEVEGRSA

19 Regional Aerosol Events are not Resolved by CMAQ: Feb 24, 1996 (Day 55)

20 Regional Aerosol Chemistry: Feb 21 & 24, /24/96 2/21/96

21 Uncertainties in Modeling Asian Impact on U.S. PM Asian Emissions - timing and location –Desert dust (Takla Makan & Gobi) –Anthropogenic dust (Loess Plateau) –Urban / Industrial / Transportation Sources Global Transport - meteorology and process –Spatial resolution –Aerosol processing N.A. Regional Transport - emissions and meteorology –Source location and activity –Wind fields –Rough terrain

22 Conclusions Asian aerosol is a dominant component of the “regional background” for rural PM in the Western U.S. The Asian “background” concentration is highly variable. Parsing the Asian aerosol flux into an “Airshed” model requires more than setting “boundary conditions.” Past contributions of Asian PM are a source of significant error in retrospective modeling. Projections of future “background” PM must include scenarios for Asian economic growth and evolving emission control programs.