m. van roozendael, amfic final meeting, 23 oct 2009, beijing, china1 maxdoas measurements in beijing...
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M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 1
MAXDOAS measurements in Beijing
M. Van Roozendael1, K. Clémer1, C. Fayt1, C. Hermans1, G. Pinardi1, R. Spurr2, P. Wang3
1 Belgian Institute for Space Aeronomy2 RT-Solutions, Inc.
3 IAP/CAS Beijing
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 2
MAXDOAS measurements principle and instrument
The retrieval algorithm
Results
Summary
OUTLOOK
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 3
MAXDOAS measurementMulti-AXis Differential Optical Absorption Spectroscopy
Use high frequency differential absorption structures to identify absorbers and quantify their abundance
DOASMAXmultiple elevation angles
from zenith to horizon
Increased sensitivity towards atmospheric absorbers present close to the surface
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 4
MAXDOAS measurement
Provides information on the vertical distribution of gases and aerosols in the troposphere.
dssSCDL
0
)(
Vertical distribution of the gas
Light path
aerosol
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 5
The instrumentGeneral features:
2-channels grating spectrometer (300 700 nm)
Low noise CCD detectors Highly accurate pointing with
sun tracking capability Thermal stabilisation high
stability High performance system
optimised for minor trace gas detection
Funded by Belspo within bi-lateral agreement with IAP
Operated at IAP from June 2008 until April 2009
Donation procedure ongoing – Feb. 2010 onwards
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 6
UV channel
VIS channel
O3
SO2
HCHO, HONO
BrO
O4, NO2
NO2, glyoxal
O3
O4, NO2
O4
O4 O2
H2O
Molecules and spectral bands
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 7
MAXDOAS measurements
The retrieval algorithm
Aerosol and NO2 results
Summary
OUTLOOK
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 8
Forward model
Calculate radiances and O4 and NO2 DSCD @ different wavelengths and viewing geometries for a given atmosphere.
INPUTS: - P, T - Surface albedo - Trace gases (,) - Aerosol (extinction profile
single scattering albedo phase function)
Linearized radiative transfer code (LIDORT v3.3) (R. Spurr, 2007)
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 9
Optimal Estimation method (Rodgers, 2000)
x = NO2 vertical profile
xa= apriori NO2 vertical profileSa = uncertainty covariance matrix of the apriori profile
F = Forward model (LIDORT)y = measurement (NO2 DSCD)S = uncertainty covariance matrix of the measurement
K = weighting functions = y/x
Advantage of LIDORT : analytical calculation of K
The inversion
aiaiTii
Tiaii xxSxFySKKSKSxx
11111
1 )(.
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 10
The inversion
MAXDOAS spectra300-390 nm and 400-720nm
2°, 4°, 6°, 8°, 10°, 12°, 15°, 30°, and zenith
O4 DSCDstrace gas DSCDs
Radiative Transfer codeLIDORT v3.3
parameters determining the atmosphere
Pressure and temperature profilesSurface albedoTrace gas: cross-sections, VMR profilesAerosol: optical properties (single scattering albedo, phase function, extinction profile)
O4 DSCDstrace gas DSCDs
weighting functions
Optimal Estimation
Aerosol extinction vertical profileTrace gas vertical profile
12
MAXDOAS measurement
DOAS fitting
Profile inversion
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 11
MAXDOAS measurements
The retrieval algorithm
Aerosol and NO2 results
Summary
OUTLOOK
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 12
TimeseriesLocation: Beijing (N 39° 58’; E 11.6° 23’)Period: Jun. 2008 – Apr. 2009
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 13
Profiles10-Nov.-2008
Aerosol
NO2
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 14
Validation: AODCIMEL MAXDOAS
Clemer et al., in preparation for AMT (2009)
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 15
Validation: NO2
ISTP 2009, Delft, 20-Oct-09
1sin ( ) 1tropo off zengeom
tropotropo
DSCD SCD SCDVC
AMF LOS
Internal consistency
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 16
Validation: NO2
ISTP 2009, Delft, 20-Oct-09
In-situ monitoring stations
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 17
Validation: NO2
(1) MAXDOAS versus in-situ
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 18
Validation: NO2
(1) in-situ versus in-situ
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 19
NO2 comparison with CHIMERE(1) Comparing total columns
Bas Mijling, KNMI
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 20
(2) Comparing partial columns
NO2 comparison with CHIMERE Bas Mijling, KNMI
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 21
Bas Mijling, KNMI
NO2 comparison with CHIMERE(3) Comparing profiles
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 22
NO2 reduction during the Olympics
Reduction of 47% during the Olympics. Less than reported by Mijling et al, probably due to non-complete recovery of pre-Olympics pollution levels in 2009.
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 23
GOME-2 and OMI NO2 validation
NO2 VCD
JJA SON
DJF MAM
OMI
Compare closest pixel within 50 km radius around Beijing
Exclude cloudy pixels (flag OK)
Compare MAXDOAS columns to GOME-2 and OMI, both derived from TEMIS approach
Extract MAXDOAS columns at satellite overpass time
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 24
GOME-2 and OMI NO2 validationGOME-2
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 25
GOME-2 and OMI NO2 validationGOME-2OMI
OMI columns 22% smaller than GOME-2 columns, in average during period of MAXDOAS measurements. More work needed to understand this difference.
OMI columns 22% smaller than GOME-2 columns, in average during period of MAXDOAS measurements. More work needed to understand this difference.
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 26
MAXDOAS measurements
The retrieval algorithm
Results
Summary
OUTLOOK
M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China 27
MAXDOAS measurements contain information on aerosol and trace gas vertical profiles
Aerosol: Good correlation with CIMEL AODs NO2: reasonable correlation with in-situ
measurements of the surface layer concentration NO2: VC correlate well with model results
(CHIMERE) Surface layer concentration lower than in-situ
but higher than CHIMERE NO2 column reduction of 47% during olympics
compared to post-olympics levels in 2009. 22% discrepency between GOME-2 and OMI NO2,
when compared to MAXDOAS.
Summary
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