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

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(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