Transcript Slide 1
Dalhousie University Department of Physics and Atmospheric Science
Research in Theoretical, Experimental, and Applied Physics
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Materials Science
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Biophysics
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Condensed Matter Physics
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Atmospheric Science
http://www.physics.dal.ca/files/Physics_and_Atmospheric_Science_Faculty.ppt
Ozone and Aerosols in the Lower Atmosphere Randall Martin Aaron Van Donkelaar Kelly Chance Chris Sioris Arlene Fiore
GLOBAL RADIATIVE FORCING OF CLIMATE, 1750-present IPCC [2001]
ORIGIN OF ATMOSPHERIC AEROSOLS Aerosol: dispersed condensed matter suspended in a gas Size range: 0.001
m
m (molecular cluster) to 100
m
m (small raindrop) Soil dust Sea salt Environmental importance: health (respiration), visibility, radiative balance, cloud formation, heterogeneous reactions, delivery of nutrients…
COMPOSITION OF PM2.5 (NARSTO PM ASSESSMENT)
Esther (1995-99) 4.6 ug m -3 Egbert (1994-99) 8.9 ug m -3 Abbotsford (1994-95) 7.8 ug m -3 Toronto (1997-99) 12.3 ug m -3 Sulfate Nitrate Ammonium Black carbon Organic carbon Soil Other St. A ndrews (1994-97) 5.3 ug m -3 Fresno (1988-89) 39.2 ug m -3 Quaker City OH (1999) 12.4 ug m -3 Kern Wildlife Refuge (1988-89) 23.3 ug m -3 Arendstville PA (1999) 10.4 ug m -3 Los Angeles (1995-96) 30.3 ug m -3 Mexico City - Netzahualcoyotl (1997) 55.4 ug m -3 Washington DC (1996-99) 14.5 ug m -3 Colorado Plateau (1996-99) 3.0 ug m -3 Mexico City - Pedregal (1997) 24.6 ug m -3 Yorkville (1999) 14.7 ug m -3 Atlanta (1999) 19.2 ug m -3
Scattering of Radiation
Size Parameter:
x
= 2p
r
/l
Mie Theory
Extinction = Scattering + Absorption Extinction Efficiency (Q ext ) = ratio of the extinction cross section to the geometric cross-section ( πr 2 )
MODerate-resolution Imaging Spectroradiometer (MODIS)
Seven
MODIS
properties bands are available for aerosol 0.47, 0.55, 0.65, 0.86, 1.24, 1.64, and 2.13 µm
OCEAN
reflectance contrast between cloud-free atmosphere and dark ocean aerosol optical thickness for all 7 bands
LAND
reflectance of dark vegetation and semi-arid regions deduced using 2.13 µm where aerosols are nearly transparent reflectance contrast between atmosphere and dense dark vegetation surface aerosol optical thickness (0.47 and 0.66 µm)
Optical Thickness = 0 0
Q ext
p
r
2
n
dr dz
I=I o e
What do we actually see?
Apollo 17 1972
Aerosols Visible over Dark Surface Mar 3, 2003
Example Cloud and Aerosol Optical Thickness
Aerosol Optical Thickness (550 nm) Cloud Optical Thickness
TROPOSPHERIC OZONE IS A KEY SPECIES IN CLIMATE AND AIR QUALITY Stratopause Mesosphere
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Major greenhouse gas
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Primary constituent of smog
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Largely controls atmospheric oxidation Stratosphere Ozone layer Tropopause Troposphere
THE ATMOSPHERE IS AN OXIDIZING MEDIUM Reduced gas EARTH SURFACE Emission Oxidation Oxidized gas/ aerosol Uptake Reduction
Simplified Tropospheric Ozone (O 3 ) Chemistry O 3
hv, H 2 O
NO 2
hv
NO x NO OH HO x
CO, VOCs
HO 2
OH
HNO H 2 O 2 3
CO, VOCs, NO x
Role of Formaldehyde (HCHO) VOCs + OH
HCHO HCHO + h
2HO 2 + CO HCHO + OH
HO 2 + CO + H 2 O
THE NITROGEN CYCLE: MAJOR PROCESSES ATMOSPHERE N 2 combustion lightning NO oxidation biofixation orgN BIOSPHERE decay assimilation NH 3 /NH 4 + denitri fication nitrification HNO 3 deposition NO 3 weathering burial LITHOSPHERE
SOILS 5 NO x EMISSIONS (Tg N yr -1 ) TO TROPOSPHERE LIGHTNING 6 STRATOSPHERE 0.2
FOSSIL FUEL 20 BIOMASS BURNING 5 BIOFUEL 2 AIRCRAFT 0.5
EULERIAN
RESEARCH MODELS SOLVE MASS BALANCE (alias CONTINUITY) EQUATION IN 3-D ASSEMBLAGE OF GRIDBOXES
n
t
=
Solve continuity equation for individual gridboxes
n
u x x
u y
y
u
z z
P
L
E
D
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Models can presently afford ~ 10 6 gridboxes
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In global models, this implies a horizontal resolution of 100-500 km in horizontal and ~ 1 km in vertical
BOTTOM-UP EMISSION INVENTORIES ARE NOTORIOUSLY DIFFICULT TO DETERMINE
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Fuel use estimates Measurements of emission ratios Process studies Estimate biological density Temperature, water, … dependence of biological activity Extreme events
Absorbing properties of molecules
Atmospheric trace gas absorptions detected in satellite spectra: 1E+16 1E+14 1E+12 1E+10 1E+08 200
O 3 UV HCHO
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SO 2 OClO O 4 H O 2 2 O BrO
400 Satellite group: http://giger.iup.uni-heidelberg.de/ 500 Wavelength [nm] 600 700 800
NO 2 O 3 vis
Retrieval of Trace Gas Column Solar I o Backscattered intensity I B
I B
Nonlinear least-squares fitting
( l ) =
A
( l )
I
0 ( l )
e
s
Ring
Scattering by Earth surface and by atmosphere A EARTH SURFACE
Total NO 2 Slant Columns Observed from the SCIAMACHY Satellite Instrument May-August 2004
Perform a Radiative Transfer Calculation to Account for Viewing Geometry and Scattering Cloud Screening: Remove Scenes with I B,c > I B,o I B,o I B,c
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LIDORT Radiative Transfer Model [Spurr et al., 2002]
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FRESCO Clouds Fields [Koelemeijer et al., 2002]
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GOME Surface Reflectivity [Koelemeijer et al., 2003] d
R s R o R c I o
q
P c
Tropospheric NO 2 Columns Observed from the SCIAMACHY Satellite Instrument May-August 2004 detection limit
Major Urban Centers Are Concentrated NOx Sources May-August 2004 detection limit
Ozone Control Strategies Require Independent Information on Effectiveness of Reducing NOx or VOCs Shown that the HCHO/NO 2 Ratio Is as Indicator That Can be Observed from Space (ppbv) NO x -Saturated NO x -Limited Sillman and He, 2002
GOME Observations Show NO x -Sensitive Conditions Over Most Polluted Regions During August Major Industrial Areas are Clear Exceptions White areas indicate clouds or data below the GOME detection limit August
Biomass Burning Emissions are Clearly NO x -Sensitive, In Contrast with NO x -Saturated Conditions Over the Industrial Highveld Also observe plume evolution August
Seasonal Evolution from NOx-Sensitive to NOx-Saturated Conditions in Fall