1. Global Climatology of Fine Particulate Matter Concentrations Estimated from Remote-Sensed Aerosol Optical Depth
Aaron van Donkelaar1, Randall Martin1,2, Ralph Kahn3 and Robert Levy3
AGU Fall Meeting
December 13-18, 2009
1Dalhousie University 2Harvard-Smithsonian 3NASA Goddard

2. Approach Estimated PM2.5 = η· τ η
We relate satellite-based measurements of aerosol optical depth to PM2.5 using a global chemical transport model
Following Liu et al., 2004:
Estimated PM2.5 = η· τ
Combined MODIS/MISR
Aerosol Optical Depth
vertical structure
aerosol type
meteorological effects
meteorology
diurnal effects η
GEOS-Chem

3. MODIS and MISR τ τ [unitless] MODIS τ MISR τ MODIS MISR
Mean τ at 0.1º x 0.1º
MODIS τ
1-2 days for global coverage
Requires assumptions about surface reflectivity
MODIS
r = 0.40
vs. in-situ PM2.5
MISR τ
6-9 days for global coverage
Simultaneous surface reflectance and aerosol retrieval
MISR
r = 0.54
vs. in-situ PM2.5
τ [unitless]

4. Agreement varies with surface type
July
MODIS
MISR
9 surface types, defined by monthly mean surface albedo ratios,
evaluation against AERONET AOD

5. Combining MODIS and MISR improves agreement
0.3
0.25
0.2
0.15
0.1
0.05
Combined
MODIS/MISR
r = 0.63 (vs. in-situ PM2.5)
τ [unitless]
MODIS
r = 0.40
(vs. in-situ PM2.5)
MISR
r = 0.54
(vs. in-situ PM2.5)

6. Global CTMs can directly relate PM2.5 to τη
[ug/m]
Detailed aerosol-oxidant model
2º x 2.5º
54 tracers, 100’s reactions
Assimilated meteorology
Year-specific emissions
Dust, sea salt, sulfate-ammonium-nitrate system, organic carbon, black carbon, SOA
GEOS-Chem

7. Significant agreement with coincident ground measurements over NA
MODIS τ
0.40
MISR τ
0.54
Combined τ
0.63
Combined PM2.5
0.78
Annual Mean PM2.5 [μg/m3] ( )
Satellite
Derived
Satellite-Derived [μg/m3]
In-situ
In-situ PM2.5 [μg/m3]

8. Method is globally applicable
Annual mean measurements
Outside Canada/US
244 sites (84 non-EU)
r = 0.83 (0.91)
slope = 0.86 (0.84)
bias = 1.15 (-2.52) μg/m3

9. High global PM2.5 exposure
WHO Guideline
AQG IT-3 IT-2 IT-1
100 90 80 70 60 50 40 30 20 10
Satellite-PM2.5 + population map → exposure
80% of world population exceeds WHO guideline of 10 μg/m3
49% of eastern Asia exceeds 35 μg/m3
Population [%]
PM2.5 Exposure [μg/m3]