Transcript NO 2

MAXDOAS observations in
Beijing
G. Pinardi, K. Clémer, C. Hermans, C. Fayt,
M. Van Roozendael
BIRA-IASB
Pucai 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
MAXDOAS instrument
• 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 analysis
DOAS analysis:
SO2
O3 (Huggins)
HCHO
HONO
UV channel
O4, NO2
SO2
HCHO, HONO
O3
BrO
BrO
NO2
Glyoxal
O3 (Chappuis)
VIS channel
O4 (360 nm)
O
O4 (4703nm)
NO2, glyoxal O , NO
4
2
O4 (570 nm) H O
2
O4
O4
O4 (630 nm)
O2
MAXDOAS retrieval strategies
Multi-Axis geometry: by collecting light at different elevations, from the
horizon to the zenith, stratospheric and tropospheric contributions can be
separated :
Multi axis pointing
Stratosphere
• constant light path through the stratosphere
• long light path through the lower troposphere,
especially for the low elevation angles
Trop SC = SCoff - SCzenith
Low
Troposphere
Line of Sight
1rst approach:
Assuming that the NO2 layer is below
the scattering altitude, a geometrical
approximation can be used to obtain
tropospheric vertical columns:
VCtrop 
SCoff axis  SCzenith
sin 1 ( LOS )  1
 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
MAXDOAS retrieval strategies
Multi-Axis geometry: by collecting light at different elevations, from the
horizon to the zenith, stratospheric and tropospheric contributions can be
separated :
Multi axis pointing
Stratosphere
Low
Troposphere
• constant light path through the stratosphere
• long light path through the lower troposphere,
especially for the low elevation angles
Line of Sight
1rst approach:
Assuming that the NO2 layer is below
the scattering altitude, a geometrical
approximation can be used to obtain
tropospheric vertical columns:
VCtrop 
SCoff axis  SCzenith
sin 1 ( LOS )  1
 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
MAXDOAS retrieval strategies
2nd approach: MAXDOAS retrieval algorithm
Using radiative transfer modeling and optimal estimation method (involving
aerosols profile retrieval from O4 DSCD) to invert tropospheric NO2 profiles
MAXDOAS retrieval strategies
2nd approach: MAXDOAS retrieval algorithm
First step: derivation of aerosol AODs from O4 and comparison with CIMEL
 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*0.8
 MAXDOAS AOD compared with available CIMEL
measurements (only two wavelengths)
MAXDOAS retrieval strategies
2nd approach: MAXDOAS retrieval algorithm
Second step: derivation of NO2 profiles and comparison of the tropospheric
columns with the geometrical approximation
Comparisons with satellites
NO2: OMI and GOME-2 (TEMIS algorithm)
Comparison with CHIMERE
CHIMERE model:
 Resolution 0.25°x0.25°
 Emissions: adapted for China
 Levels (8, until 500 hPa (5.5 km))
 ECMWF data set (0.5°)
Bas Mijling presentation
Type of output:
 One file per day
 NO2, HCHO, Glyoxal,
SO2 profiles (8 levels),
for each cell, 1 output
per hour
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
Comparison with CHIMERE
 CHIMERE cell: 0.25°x0.25°
(which at the Beijing latitude
is ~28x21km²)
50 and 100 Km
Beijing
CHIMERE cells
Spatial and temporal variations (1)
GOME-2 pixel: 40x80km²
OMI pixel: 13x24km²
Spatial and temporal variations (2)
GOME-2 pixel: 40x80km²
OMI pixel: 13x24km²
Under-development!!
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.
Other trace gases…
HCHO: (Glyoxal, SO2)
 MAXDOAS vs CHIMERE ☺
 SCIAMACHY and GOME-2
 will be presented by I. De
Smedt
day 20081130
day 20080802
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