us aerosols: observation from space, interactions with climate daniel j. jacob and funding from...
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US aerosols: US aerosols: observation from space, interactions with climate observation from space, interactions with climate
Daniel J. Jacob
and funding from NASA, EPRI, EPA
with Easan E. Drury, Loretta J. Mickley, Eric M. Leibensperger, Amos Tai
IMPORTANCE OF ATMOSPHERIC AEROSOLSIMPORTANCE OF ATMOSPHERIC AEROSOLS
Public health
Visibility
Ocean fertilization
Chemistry
Climate forcing
Cloud formation
number
area
volume
AEROSOL CHARACTERISTICS
Typical size distribution(Seinfeld and Pandis, 1998)
Chemical composition of PM2.5
(NARSTO, 2004)
sulfate (coal combustion)
nitrate (fossil fuel combustion)
ammonium (agriculture)
black carbon (combustion)
organic carbon (combustion,vegetation)
soil
other
PM2.5 (EPA std.)
SATELLITE OBSERVATIONS OF TROPOSPHERIC COMPOSITION:SATELLITE OBSERVATIONS OF TROPOSPHERIC COMPOSITION:
The NASA “A-Train”
Satellites
Surface sites
Models
aircraft, ships, sondes, lidars
a revolution over the past decade
Integrated observing system
Principal tropospheric species measured from space:• Ozone , NO2, formaldehyde, BrO, glyoxal• CO, CO2, methane• Aerosols, SO2
HOW TO OBSERVE AEROSOLS FROM SPACE?HOW TO OBSERVE AEROSOLS FROM SPACE?
EARTH
Solar occultation (SAGE, POAM…)
Pros: high S/N, vertical profilingCons: sparse sampling, cloud interference, low horizontal resolution
Active system(CALIPSO…)
Pro: vertical profilingCon: sparse sampling,low S/N
Pro: horiz. resolutionCon: daytime only, no vertical resolution
Solar back-scatter(MODIS, MISR…)
laserpulse
Surface Surface
Aerosol observation from space by solar backscatterAerosol observation from space by solar backscatter
Pollution off U.S. east coast Dust off West AfricaCalifornia fire plumes
Relatively easy to do qualitatively for thick plumes over ocean…
I
II ()exp[-AOD]
…but difficult quantitatively! Fundamental quantity is aerosol optical depth (AOD)
aerosol scattering, absorption
Measured top-of-atmosphere reflectance = f (AOD, aerosol properties, surface reflectance, air scattering, gas absorption, Sun-satellite geometry)
Aerosol optical depths (AODs) measured from spaceAerosol optical depths (AODs) measured from space
Jan 2001 – Oct 2002 operational data
MODIS (c004)return time 2x/day;nadir viewknown positive biasover land
MISR9-day return time;multi-angle viewbetter but much sparser
van Donkelaar et al. [2006]
550 nmAODs
MODIS AEROSOL RETRIEVAL OVER LANDMODIS AEROSOL RETRIEVAL OVER LAND
SURFACE
0.47 m0.65 m2.13 m
Operational retrieval: Use top-of-atmosphere (TOA) reflectance at 2.13 m (transparent atmosphere) to derive surface reflectance Assume fixed 0.47/2.13 and 0.65/2.13 surface reflectance ratios to derive atmospheric reflectances at 0.47 and 0.65 m by subtraction Assume generic aerosol optical properties to convert atmospheric reflectance to AOD
Our improved retrieval: Derive local values of 0.47/2.13 and 0.65/2.13 surface reflectance ratios from statistics of low-aerosol scenes Use local aerosol column information from the GEOS-Chem chemical transport model to convert atmospheric reflectance to AOD
TOAreflectance
Drury et al. (JGR in press)
GEOS-Chem CHEMICAL TRANSPORT MODEL (geos-chem.org)GEOS-Chem CHEMICAL TRANSPORT MODEL (geos-chem.org)
• Global model of atmospheric composition driven by NASA/GEOS assimilated meteorological data with 0.5ox0.625o (~50 km) resolution
• Simulates coupled oxidant-aerosol chemistry for
• sulfate-nitrate ammonium• organic aerosol• black carbon aerosol• dust (4 size classes)• sea salt (2 size classes)
on 2o x2.5o grid
• Size distributions and optical properties for different aerosol types are specified
TESTING THE MODIS AEROSOL RETRIEVALTESTING THE MODIS AEROSOL RETRIEVALUSING ICARTT AIRCRAFT DATA OVER US (Jul-Aug 2004)USING ICARTT AIRCRAFT DATA OVER US (Jul-Aug 2004)
EASTERN U.S.
EPA AQS/IMPROVE surface networks: mass concentrationsNASA AERONET surface network: AODs
NASA, NOAA, DOE aircraft: speciated mass concentrations,microphysical & optical properties
MODIS satellite instrument:TOA reflectance
GEOS-Chem model
evaluate
MODIS local surfacereflectanceand ratio
synthetic TOAreflectance = f(AOD,…)
fit AODs
Drury et al. [JGR in press]
NASADC-8
ORGANIC AEROSOL IN ICARTTORGANIC AEROSOL IN ICARTT
• Standard reversible SOA (Pankow/Seinfeld):( , )oxidationVOC secondary organic gas (SOG) SOA
K T aerosol • Dicarbonyl SOA (Liggio/Fu):
oxidation cloud uptakemulti-step oxidation, oligomerization
VOC glyoxal, methylglyoxal SOA
Water-soluble organic carbon (WSOC) measured on NOAA P-3 IMPROVE measurements of organic carbon
Fu et al.(AE, 2009)
Two mechanisms for formation of secondary organic aerosol (SOA):
AEROSOL OPTICAL PROPERTIES IN ICARTTAEROSOL OPTICAL PROPERTIES IN ICARTT
Single-scattering albedo = fraction ofaerosol extinction due to scattering
AERONET
standard modelassumption (GADs)
improved fit(this work)
Drury et al., JGR in press
AEOSOL OPTICAL DEPTHS (0.47 AEOSOL OPTICAL DEPTHS (0.47 m), JUL-AUG 2004 m), JUL-AUG 2004
Drury et al., JGR in press
c005 is current MODIS operational data; statistics are relative to AERONET data in circles
Beyond improving on the operational products, our MODIS retrieval enables quantitative comparison to model results (consistent aerosol optical properties); indicates model underestimate in Southeast US, likely due to organic aerosol
bias=+2%r = 0.84
bias=-21%r = 0.82
bias=-15%r = 0.87
Can we use AODs measured from space as proxy for PMCan we use AODs measured from space as proxy for PM2.52.5??
2.52.5
GEOS-Chem
PMPM = AOD*
AOD
MODIS PM2.5 (this work)EPA AQS surface network data
Infer PM2.5 from AOD by
MODIS captures general observed patterns in PM2.5
but is 50% higher than observed. Could reflect• Clear-sky bias• Time-of-day bias• Model error in vertical aerosol distribution
Drury et al., JGR in press
RADIATIVE FORCING OF CLIMATE BY AEROSOLS
But this aerosol radiative forcing is very inhomogeneous: what are the regional climate consequences?
Anthropogenic aerosols may have offset more than half of global greenhouse warming from 1750 to present
IPCC (2007)
Leibensperger et al., in prep.
Aerosol direct radiative forcing
CLIMATE IMPLICATIONS OF US AIR QUALITY POLICY
today
US sulfur emissions are decreasing rapidly: what are the regional climate impacts?
Radiative forcing of US anthropogenic aerosols is small globally but important regionally
Leibensperger et al., in prep.
CALCULATING THE CLIMATE RESPONSE CALCULATING THE CLIMATE RESPONSE FROM SHUTTING DOWN U.S. AEROSOL FROM SHUTTING DOWN U.S. AEROSOL
Mickley et al. (AE, submitted)
Consider two scenarios: Control: aerosol optical depths fixed at 1990s levels. Sensitivity: U.S. aerosol optical depths set to zero (radiative forcing of about +2 W m-2 over US)
Conduct ensemble of 3 simulations for each scenario.
GISS GCM
Use NASA/GISS general circulation model (GCM)
Removing aerosols over US Removing aerosols over US causes 0.5-1causes 0.5-1o o C annual mean warming in the East.C annual mean warming in the East.2010-2050 warming due to
greenhouse gasesAdditional warming due to
zeroing of aerosols over the US.
Tem
pera
ture
(o C
) No-US-aerosols case
Control, with US aerosols
Mickley et al. [AE, submitted]
Additional effects include increased summer heatwaves (1-2 o C warming) and increased precipitation in the East
EFFECT OF CLIMATE CHANGE ON SURFACE AIR QUALITYEFFECT OF CLIMATE CHANGE ON SURFACE AIR QUALITY
Ozone PM (aerosol)
Stagnation
Temperature
Mixing depth
Precipitation
Cloud cover
Relative humidity
Expected effect of 21st century climate change
=
=?
?=?
?
Jacob and Winner, AE 2009
?
EFFECT OF FUTURE CLIMATE CHANGE ON US AIR QUALITYEFFECT OF FUTURE CLIMATE CHANGE ON US AIR QUALITY
MDA8
-9-8-7-6-5-4-3-2-1012345
NE MW CA TX SE
Harvard.A1B CMU.A2 PGR.B1 NERL.A1B WSU.A2 PGR.A1Fi
Northeast Midwest California Texas Southeast
2000-2050 change of 8-h daily max ozone in summer, keeping anthropogenic emissions constantppb
Models show consistent increase of ozone, mainly driven by temperature
Results from six coupled GCM-CTM simulations
Weaver et al.[BAMS, 2010]
…but model results for aerosols show no such consistency, including in sign.How can we progress?
OBSERVED AEROSOL CORRELATION OBSERVED AEROSOL CORRELATION WITH METEOROLOGICAL VARIABLESWITH METEOROLOGICAL VARIABLES
Multilinear regression model fit to 1998-2008 deseasonalized EPA/AQS data for PM2.5 (total and speciated)
9
1,,,0 n termsinteractio
kikikii xy
R2 fit
mostly precipitationmostly temperature and stagnation
Tai et al.[AE, submitted]
PMPM2.52.5 CORRELATION WITH METEOROLOGICAL VARIABLES CORRELATION WITH METEOROLOGICAL VARIABLES
Tai et al. [AE , submitted]
TEMPERATURE COEFFICIENTS FOR SPECIATED PMTEMPERATURE COEFFICIENTS FOR SPECIATED PM2.52.5
Tai et al. [AE , submitted]
IMPORTANCE OF MID-LATITUDES CYCLONES IMPORTANCE OF MID-LATITUDES CYCLONES IN AIR POLLUTION METEOROLOGYIN AIR POLLUTION METEOROLOGY
Clean air sweepsbehind cold front
Cold fronts from mid-latitude cyclones are the principal ventilation processfor U.S. Midwest/Northeast, western Europe, China
GCMs show decrease + N shift of cyclones from 21st-century climate change;already seen in 1950-2000 climatological data
CORRELATIONS AND TRENDSCORRELATIONS AND TRENDSOF POLLUTION EPISODES AND CYCLONES IN NORTHEAST U.S.OF POLLUTION EPISODES AND CYCLONES IN NORTHEAST U.S.
# pollution episode days (O3>80 ppb) and # cyclones tracking across SE Canadain summer 1980-2006 observations
Cyclone track
• Strong correlation; cyclone frequency is predictor of pollution episode frequency
• 1980-2006 decrease in cyclone frequency would imply a corresponding degradation of air quality if emissions had remained constant
• Expected # of > 80 ppb days in Northeast dropped from 30 in 1980 to 10 in 2006, but would have dropped to zero by 2001 in absence of cyclone trend!
Leibensperger et al. [ACP2008]
# cyclones# episodes
EFFECT OF INCREASED STAGNATION ON PMEFFECT OF INCREASED STAGNATION ON PM2.52.5
Difference in PM2.5 between stagnant days (wind < 8 m s-1, 500 hPa wind <13 m s-1, no precipitation) and non-stagnant days, 1998-2008 data
PM2.5 is expected to be highly sensitive to Increasing stagnation in future climate
Tai et al. [AE , submitted]
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