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New 2-channels MAXDOAS system with direct-sun pointing capability developed at BIRA Instrument funded by Belspo as part of bilateral research agreement for DRAGON-AMFIC Aim: provide complementary measurements of AQ-related gases and contribute to satellite validation (Target data products: O 3, NO 2, BrO, HCHO, glyoxal, SO 2, aerosol, etc) Operation: in Beijing at IAP/CAS from June 2008 to April Longer term: permanent installation in background site North of Beijing (Xinglong) MAXDOAS instrument
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MAXDOAS observations in Beijing
G. Pinardi, K. Clémer, C. Hermans, C. Fayt, M. Van Roozendael
BIRA-IASBPucai Wang & Jianhui Bai
IAP/CAS
24 June 2009, AMFIC meeting, Barcelona
Overview
MAXDOAS instrument MAXDOAS retrieval strategies Comparisons with satellite and CHIMERE
model (NO2, HCHO,…) Conclusions and perspectives
• New 2-channels MAXDOAS system with direct-sun pointing capability developed at BIRA
• Instrument funded by Belspo as part of bilateral research agreement for DRAGON-AMFIC
• Aim: provide complementary measurements of AQ-related gases and contribute to satellite validation (Target data products: O3, NO2, BrO, HCHO, glyoxal, SO2, aerosol, etc)
• Operation: in Beijing at IAP/CAS from June 2008 to April 2009. Longer term: permanent installation in background site North of Beijing (Xinglong)
MAXDOAS instrument
UV channel
VIS channel
O3
SO2
HCHO, HONO
BrO
O4, NO2
NO2, glyoxal
O3
O4, NO2
O4O4 O2
H2O
MAXDOAS analysisDOAS analysis:
O3 (Huggins)SO2 HCHO HONO
BrO NO2 Glyoxal O3 (Chappuis)
O4 (360 nm) O4 (470 nm) O4 (570 nm) O4 (630 nm)
Multi axis pointing• constant light path through the stratosphere • long light path through the lower troposphere, especially for the low elevation angles
Multi-Axis geometry: by collecting light at different elevations, from the horizon to the zenith, stratospheric and tropospheric contributions can be separated :
Stratosphere
Low Troposphere 1sin ( ) 1
off axis zenithtrop
SC SCVC
LOS
Assuming that the NO2 layer is below the scattering altitude, a geometrical approximation can be used to obtain tropospheric vertical columns:
Line of Sight
MAXDOAS retrieval strategies
1rst approach: QA/QC: columns derived from 2 different elevations angles (15° and 30°) are eliminated if they differ by more than 30 %.
Tropospheric columns have been derived for NO2, HCHO, CHOCHO and SO2
Trop SC = SCoff - SCzenith
Multi axis pointing• constant light path through the stratosphere • long light path through the lower troposphere, especially for the low elevation angles
Multi-Axis geometry: by collecting light at different elevations, from the horizon to the zenith, stratospheric and tropospheric contributions can be separated :
Stratosphere
Low Troposphere 1sin ( ) 1
off axis zenithtrop
SC SCVC
LOS
Assuming that the NO2 layer is below the scattering altitude, a geometrical approximation can be used to obtain tropospheric vertical columns:
Line of Sight
MAXDOAS retrieval strategies
1rst approach: QA/QC: columns derived from 2 different elevations angles (15° and 30°) are eliminated if they differ by more than 30 %.
Tropospheric columns have been derived for NO2, HCHO, CHOCHO and SO2
Using radiative transfer modeling and optimal estimation method (involving aerosols profile retrieval from O4 DSCD) to invert tropospheric NO2 profiles
MAXDOAS retrieval strategies2nd approach: MAXDOAS retrieval algorithm
AOD retrieved from 4 bands of O4 (treated independently)Correction by a factor 1/0.8 to correct the O4 xs, so the
measured O4 DSCD measured O4 DSCD*0.8MAXDOAS AOD compared with available CIMEL
measurements (only two wavelengths)
MAXDOAS retrieval strategies2nd approach: MAXDOAS retrieval algorithmFirst step: derivation of aerosol AODs from O4 and comparison with CIMEL
Second step: derivation of NO2 profiles and comparison of the tropospheric columns with the geometrical approximation
MAXDOAS retrieval strategies2nd approach: MAXDOAS retrieval algorithm
Comparisons with satellitesNO2: OMI and GOME-2 (TEMIS algorithm)
CHIMERE model: Resolution 0.25°x0.25° Emissions: adapted for China Levels (8, until 500 hPa (5.5 km)) ECMWF data set (0.5°)
Type of output: One file per day NO2, HCHO, Glyoxal, SO2 profiles (8 levels), for each cell, 1 output per hour
Comparison with CHIMERE
Work under-progress: comparison with MAXDOAS at Beijing «simulation» of the NO2 field seen by OMI
Use CHIMERE as transfer standard to link satellite and ground-based column measurements
Bas Mijling presentation
Comparison with CHIMERE CHIMERE cell: 0.25°x0.25° (which at the Beijing latitude is ~28x21km²)
CHIMERE cells
50 and 100 Km
Beijing
GOME-2 pixel: 40x80km² OMI pixel: 13x24km²
Spatial and temporal variations (1)
GOME-2 pixel: 40x80km² OMI pixel: 13x24km²
Spatial and temporal variations (2)
Depending on the relative position of the satellite closest pixel, a weighted average of several CHIMERE grid cells is performed in order to reproduce the spatial averaging performed by the satellite.
Under-development!!
HCHO: (Glyoxal, SO2)
MAXDOAS vs CHIMERE ☺
SCIAMACHY and GOME-2 will be presented by I. De Smedt
Other trace gases…
day 20080802day 20081130
Summary and Perspectives
MAXDOAS has measured in Beijing from June 2008 to April 2009 future re-installation outside Beijing
2 retrieval strategies show good agreement One wrt the other for tropospheric NO2 With CIMEL for the aerosols (AOD)
Tropospheric NO2 and HCHO time series are compared to satellites (CHOCHO, SO2 also possible)
Comparisons with the CHIMERE model is under development
Idea: study the temporal and spatial variability and the effects of horizontal smoothing