M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China1 MAXDOAS measurements in Beijing M. Van Roozendael 1, K. Clémer 1, C. Fayt 1, C. Hermans 1, G. Pinardi 1, R. Spurr 2, P. Wang 3 1 Belgian Institute for Space Aeronomy 2 RT-Solutions, Inc. 3 IAP/CAS Beijing

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China2  MAXDOAS measurements  principle and instrument  The retrieval algorithm  Results  Summary OUTLOOK

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China3 MAXDOAS measurement Multi-AXis Differential Optical Absorption Spectroscopy  Use high frequency differential absorption structures to identify absorbers and quantify their abundance DOASMAX multiple 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, China4 MAXDOAS measurement  Provides information on the vertical distribution of gases and aerosols in the troposphere. Vertical distribution of the gas  Light path aerosol

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China5 The instrument General 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 onwards

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China6 UV channel VIS channel O3O3 SO 2 HCHO, HONO BrO O 4, NO 2 NO 2, glyoxal O3O3 O 4, NO 2 O4O4 O4O4 O2O2 H2OH2O Molecules and spectral bands

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China7  MAXDOAS measurements  The retrieval algorithm  Aerosol and NO 2 results  Summary OUTLOOK

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China8 Forward model  Calculate radiances and O 4 and NO 2 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, China9  Optimal Estimation method (Rodgers, 2000) x = NO 2 vertical profile x a = apriori NO 2 vertical profile S a = uncertainty covariance matrix of the apriori profile F = Forward model (LIDORT) y = measurement (NO 2 DSCD) S  = uncertainty covariance matrix of the measurement K = weighting functions =  y/  x Advantage of LIDORT : analytical calculation of K The inversion

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China10 The inversion MAXDOAS spectra nm and nm 2°, 4°, 6°, 8°, 10°, 12°, 15°, 30°, and zenith O 4 DSCDs trace gas DSCDs Radiative Transfer code LIDORT v3.3 parameters determining the atmosphere Pressure and temperature profiles Surface albedo Trace gas: cross-sections, VMR profiles Aerosol: optical properties (single scattering albedo, phase function, extinction profile) O 4 DSCDs trace gas DSCDs weighting functions Optimal Estimation Aerosol extinction vertical profile Trace gas vertical profile 1 2 MAXDOAS measurement DOAS fitting Profile inversion

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China11  MAXDOAS measurements  The retrieval algorithm  Aerosol and NO 2 results  Summary OUTLOOK

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China12 Timeseries Location: Beijing (N 39° 58’; E 11.6° 23’) Period: Jun – Apr. 2009

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China13 Profiles 10-Nov Aerosol NO 2

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China14 Validation: AOD CIMELMAXDOAS Clemer et al., in preparation for AMT (2009)

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China15 Validation: NO 2 ISTP 2009, Delft, 20-Oct-09 Internal consistency

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China16 Validation: NO 2 ISTP 2009, Delft, 20-Oct-09 In-situ monitoring stations

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China17 Validation: NO 2 (1) MAXDOAS versus in-situ

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China18 Validation: NO 2 (1) in-situ versus in-situ

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China19 NO 2 comparison with CHIMERE (1) Comparing total columns Bas Mijling, KNMI

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China20 (2) Comparing partial columns NO 2 comparison with CHIMERE Bas Mijling, KNMI

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China21 Bas Mijling, KNMI NO 2 comparison with CHIMERE (3) Comparing profiles

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China22 NO 2 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, China23 GOME-2 and OMI NO 2 validation NO 2 VCD JJASON DJFMAM 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, China24 GOME-2 and OMI NO 2 validation GOME-2

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China25 GOME-2 and OMI NO 2 validation GOME-2 OMI 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, China26  MAXDOAS measurements  The retrieval algorithm  Results  Summary OUTLOOK

M. Van Roozendael, AMFIC Final Meeting, 23 Oct 2009, Beijing, China27  MAXDOAS measurements contain information on aerosol and trace gas vertical profiles  Aerosol: Good correlation with CIMEL AODs  NO 2 : reasonable correlation with in-situ measurements of the surface layer concentration  NO 2 : VC correlate well with model results (CHIMERE)  Surface layer concentration lower than in-situ but higher than CHIMERE  NO 2 column reduction of 47% during olympics compared to post-olympics levels in  22% discrepency between GOME-2 and OMI NO 2, when compared to MAXDOAS. Summary