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

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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]