Satellite Observations of Tropospheric Aerosols: More than Pretty Pictures
Symposium in Honour of Jennifer Logan, Harvard UniversityMay 10, 2013
Colette L. HealdMaria Val Martin, Bonne Ford, David Ridley
Let’s not forget: an institution that trained
Jennifer Logan!
Challenge: Heterogeneity of Atmospheric Aerosols
GEOS-5 10 km aerosol model
http://www.nasa.gov/multimedia/imagegallery/image_feature_2393.html
Many first order problems in aerosols (how much? what sources?) challenging to address because of the short lifetimes and varying properties of particles in the atmosphere.
Solution: Satellites!
1. Identify air masses 2. Context (spatial and temporal)3. Track (investigate processing)4. Identify sources5. Constrain Budgets
Transpacific Transport of Asian Aerosol Pollution as Seen by MODIS
April 25, 2001
April 26, 2001
April 27, 2001
Most basic use of satellite observations (Identify events)
MODIS AODGEOS-Chem
dust AODGEOS-Chem Asian
sulfate AOD
[Heald et al., 2006]
Satellite Measurements Show How High Aerosol Loading (AOD) is Associated with Both Local and Transported Smoke
June 2002
[val Martin et al., submitted]
MODIS Terra AOD anomaliesAugust 2012
Hayman Fire
High Park andWaldo Fires
AZ Wallow Fire(2011)
MT, WY, ID, WA FiresAZ, CA
FiresCA Station Fire
(2009)
Continuous satellite observations can integrate across events and regions (Context)
Dust From North Africa: Using Satellite Observations to Test Sources, Properties and Transport
Air Quality (local & Americas)
Ocean Fertilization (C cycle)
Nutrient Supply(terrestrial productivity)
[Highwood et al., 2003]
Observed Saharan dust size distribution
Simulated decrease in AOD
Shifted mass to larger sub-micron sizes (less optically efficient). Reduces AOD in better agreement with satellite & AERONET observations
Dust Removal Across the Atlantic
Model removal too strong, especially in winter-spring (transport towards Amazon).Likely excessive removal along the ITCZ.
We estimate dust lifetimes in model (~3 days) in spring about 50% of satellite-based estimate (> 6 days).
(Aerosol processing)
Assuming first order loss can estimate lifetime from slope of log-plots…
[Ridley et al., 2012]
Atmospheric Ammonia: A Source of Particulate Matter and Emissions on the Rise…
AnimalsAgriculture
NH3 emissions major source of fixed N
atmospheric acids (H2SO4, HNO3)
Haber-Bosch Process (industrial production of NH3 fertilizer) has
dramatically increased global food production.
…degrading air quality?now and in the future?
Atmospheric NH3 is sticky and semi-volatile with large dynamic range of
concentrations: Difficult to measure.
[Erisman et al., 2008]
+ =
Satellite Observations Providing Critical New Insights!
New satellite measurements from IASI
offer unprecedented monitoring of NH3.
Comparison with GEOS-Chem reveals springtime
underestimate of emissions in the
Midwest and year-round underestimate in the
Central Valley of California.
(Identify sources)
[Heald et al., 2012]
The Importance and Challenge(s) of Organic Aerosol
Globally OA makes up 25-75% of total fine aerosol at the surface. Could become more even more important in the future with sulfate clean-up?
Models drastically underestimate. Source(s) unclear.
[Heald et al., 2011]
VOCs
Range = 0.45-4.5
Primary
Secondary
oVOCs
?
Average aerosol composition for 37 campaigns in the NH
[Zhang et al., 2007]
Model-measurement comparison for 17 aircraft campaigns
Using Satellite Observations to Constrain the Global Budget of Organic Aerosol
[Heald et al., 2010b]
Summer
MISR AOD
Simulated AOD from
OTHER aerosol
Residual =
Organic Aerosol
Satellite measurements indicate that total OA source is capped at 150 TgC/yr. This is still 3 times what is currently included in models.
(Constrain budgets)
TgC/yr
Is Organic Aerosol Contributing to Climate Trends in the SE US? Portmann et al. [2009] suggest cooling over the E. US (1950 to present) associated with biogenic
aerosol. Goldstein et al. [2009] show large AOD enhancement over SE in summer.
Strong seasonality seen in satellite AOD, but not surface PM2.5. Explanation: aerosol aloft confirmed by CALIOP – inorganic or organic? SENEX 2013!
(Reveal interesting disconnects, probe 3D distribution)[Ford and Heald, submitted]
DJF JJA
CALIOPGEOS-Chem
Conclusions
Funding Acknowledgements:
Satellite measurements fill much needed observational gap for aerosols
But quantitative comparisons (moving beyond pretty pictures) can be challenging.
1. Interpretation of an integrated measurement (AOD), with complex retrieval algorithms. True uncertainties and biases not easily explored.
2. Retrieval algorithms not easily mimic’ed for models
3. Limited suite or sensitivity of aerosol precursor measurement from space (SO2, NH3, VOCs).
4. Daily snapshots (polar orbit) limit process quantification
First ever Official Atmospheric Chemistry Modeling Group Photo (2003)
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