1. MODELING TRANSPORT OF OZONE AND FINE PARTICLES TO AND FROM NORTH AMERICA
Daniel J. Jacob
Harvard University
with Arlene M. Fiore, Rokjin Park, Colette L. Heald
and support from EPA (ICAP), EPRI, NOAA

2. TWO MODES OF INTERCONTINENTAL INFLUENCE
Direct intercontinental transport: fast (~1 week) transport from source to receptor continent; either by boundary layer advection or by lifting to lower free
troposphere followed by subsidence
Hemispheric pollution: pollution mixes in free troposphere, affecting free tropospheric background, in turn affecting surface concentrations by subsidence
Tropopause
HEMISPHERIC POLLUTION BACKGROUND
Mixing
Free troposphere
2 km
“Direct”
intercontinental
transport
Boundary layer
boundary layer advection
lifting
subsidence
Asia
N. America
Europe

3. MECHANISM FOR TRANSPACIFIC TRANSPORT OF ANTHROPOGENIC OZONE AND FINE PARTICLES
HEMISPHERIC POLLUTION
PAN (~10%)
VOCs
(long-lived)
warm conveyor belts,
convection
subsidence O3 OC
aerosol
PAN
Free
troposphere
SOx (~10%)
sulfate
NOx O3
2 km
Boundary layer
entrainment,
dilution
NOx, SO2, VOC
aerosols,
HNO3
ozone, sulfate, OC
ASIA PACIFIC NORTH AMERICA

4. USING GLOBAL CHEMICAL TRANSPORT MODELS TO QUANTIFY INTERCONTINENTAL INFLUENCE
Standard simulation; compare w/ observations
(2) Set N. American anthropogenic emissions to zero a estimate background
(3) Set global anthropogenic emissions to zero a estimate natural background
Difference between (1) and (2) a regional pollution
Difference between (2) and (3) a intercontinental pollution
GEOS-Chem model :
driven by NASA/GEOS assimilated meteorological data
horizontal resolution 2ox2.5o, 48 vertical levels
coupled ozone-PM simulation
used by 20 research groups in Europe and N. America (~100 publications)
extensive evaluation with U.S. observations for ozone [Fiore et al., 2002, 2003ab] and PM [Park et al., 2003, 2004]

5. Surface ozone at Voyageurs National Park, Minnesota (May-June 2001)*
CASTNet observations
Model
Background
Natural
Stratospheric }
Regional
pollution
D =
Surface ozone at Voyageurs National Park, Minnesota (May-June 2001) }
D =
Intercontinental
pollution + X
Background: ppbv
Natural : 9-23 ppbv
Stratosphere: < 7 ppbv
Fiore et al. [2003]

6. *
CASTNet observations
Model
Background
Natural O3 level
Stratospheric }
Regional
pollution
D =
Surface ozone at Yellowstone National Park, Wyoming, 2.5 km altitude (March-May 2001) }
D =
Intercontinental
pollution + X
Background: ppbv
Natural : ppbv
Fiore et al. [2003]

7. Probability. ppbv-1 Ozone, ppbv
Probability distribution of afternoon (1-5 p.m. mean) surface ozone at U.S. CASTNet sites in March-October 2001
Natural 18±5 ppbv
GEOS-Chem
background 26±7 ppbv
GEOS-Chem
background 29±9 ppbv
MOZART-2
Probability. ppbv-1
CASTNet observations
GEOS-Chem at CASTNet
Ozone, ppbv
Intercontinental pollution enhances background by 8 ± 4 ppbv relative to natural
Fiore et al. [2003]

8. DEPLETION OF OZONE BACKGROUND DURING REGIONAL POLLUTION EPISODES
Low-elevation CASTNet sites, Jun-Aug
CASTNet observations
GEOS-Chem model
Model background *
Regional
Pollution
Ozone (ppbv)
Cumulative Probability
Background (and intercontinental pollution influence) are highest when ozone concentrations are in mid-range (40-70 ppbv), reflecting subsidence conditions
Fiore et al. [2003]

9. GLOBAL OZONE BACKGROUND: METHANE AND NOx ARE THE LIMITING PRECURSORS
Sensitivity of global tropospheric ozone inventory (Tg) to 50% global reductions
In anthropogenic precursor emissions
GEOS-Chem [Fiore et al., 2002a]
Anthropogenic methane enhances surface ozone by 4-6 ppbv worldwide

10. INCREASE IN FREE TROPOSPHERIC BACKGROUND OZONE OVER EUROPE IN THE PAST CENTURY
Simulated historical ozone levels are higher than observed: is this due to
model overestimates in natural sources (lightning) or calibration errors?
Observations at mountain sites [Marenco et al., 1994]
Preindustrial
model ranges

11. OBSERVED TREND IN OZONE BACKGROUND OVER CALIFORNIA IN SPRING SUGGESTS ppbv INCREASE OVER PAST 20 YEARS
Trend: ppbv yr-1
Jaffe et al. [2003]
…but this is inconsistent with models; e.g., GEOS-Chem model indicates only a 2 ppbv increase over (Fiore et al., 2002b)

12. AN EXAMPLE OF TRANSPACIFIC TRANSPORT OF ASIAN AEROSOL POLLUTION AS SEEN BY MODIS
X1018 [molecules cm-2]
Detectable sulfate pollution signal correlated with MOPITT CO

13. WET SCAVENGING OF ASIAN AEROSOLS DURING LIFTING TO THE FREE TROPOSPHERE
TRACE-P observations over NW Pacific (Feb-Mar 2001)
and GEOS-Chem simulations
P3B DATA over NW Pacific (30 – 45oN, 120 – 140oE)
Sulfate is most important exported anthropogenic aerosol in model
Park et al. [2005]

14. …BUT ELEVATED OC AEROSOL IS OBSERVED IN FREE TROPOSPHERIC ASIAN OUTFLOW – CONTRIBUTION TO INTERCONTINENTAL POLLUTION?
ACE-Asia aircraft observations over Japan (spring 2001)
Observed
(Russell)
Observed (Huebert)
GEOS-Chem
correlated with CO – but also a 1-3 mg sm-3 background;
implies large secondary production of OC in free troposphere missing from present models;
OC dominates aerosol loading in free troposphere
OC/sulfate ratio
Colette .L. Heald, Harvard

15. INTERCONTINENTAL TRANSPORT OF ASIAN AND NORTH AMERICAN ANTHROPOGENIC SULFATE
Annual mean values as determined from GEOS-Chem 2001 sensitivity simulations with these sources shut off
Intercontinental enhancements of anthropogenic sulfate over U.S. are of same order as interstate enhancement threshold used for regulation (0.2 mg m-3) and EPA estimates of natural values ( mg m-3) for Regional Haze Rule
Park et al. [2004]

16. VERTICAL STRUCTURE OF TRANSPACIFIC TRANSPORT
GEOS-Chem model results for spring 2001 (15-45oN)
Asian CO Asian sulfate
Differential transport of CO and aerosols
Aerosols not diluted across Pacific and at good alt to impact surface
Asia
N. America
Asia
N. America
Asian aerosols are transported in lower free troposphere and subside over
the NE Pacific; topography in western U.S. promotes contact with surface
C.L. Heald, Harvard

17. EVIDENCE OF ASIAN SULFATE IN IMPROVE NETWORK OF AEROSOL MEASUREMENTS AT U.S. SITES
GEOS-Chem Asian influence
spring 2001 mean h seasonal max
NW US:
0.60 μgm-3
NW US:
0.18 μgm-3
1.4
mg m-3
IMPROVE
GEOS-CHEM
Asian anthr
(GEOS-Chem)
Time series over
NW U.S. (spring 01)
Most of max concentrations happen on May 19 (40%), with some on May 8 (20%) and April 16 (10%), April 25 (7%)  all events on previous plot
Sites with > 1 ug/m3 (Crater Lake, OR (May 6); Lassen, CA (April 29); Snoqualeame Pass, WA (May 7); White Pass, WA (May 6, 19))
Conclusions of study: MODIS useful for tracking transpacific transport and the transport of sulfate observed supports the model simulation
March April May June 1
IMPROVE data:
spring 2001 mean days of GEOS-Chem 24-h seasonal max
NW US:
1.04 μgm-3
NW US:
0.72 μgm-3
C.L. Heald,
Harvard