DPG 2007
UP 8.6
MAXDOAS measurements from the DANDELIONS campaigns
A. Schönhardt1*, F. Wittrock1, A. Richter1, H.Oetjen1, J. P. Burrows1, G. Pinardi2, M. v. Roozendael2, T. Wagner3,6,
O. Ibrahim3, H. Bergwerff4, S. Berkhout4, R. v.d. Hoff4, H. Volten4, D. Swart4 and E. Brinksma5
1Institute
of Environmental Physics, University of Bremen, Germany
2BIRA, Belgian Institute for Space Aeronomy, Brusseles, Belgium
3Institute of Environmental Physics, University of Heidelberg, Germany
*Email: [email protected]
Introduction
4RIVM,
National Institute for Public Health and the Environment, Bilthoven, The Netherlands
5KNMI, Royal Netherlands Meteorological Institute, De Bilt, The Netherlands
6Max Planck Institute for Chemistry, Mainz, Germany
DANDELIONS: Dutch Aerosol and Nitrogen Dioxide Experiments for Validation of OMI and SCIAMACHY
Campaign Information:
Main Objectives:
Participants in NO2 measurements:
Validation Campaign in Mai-July 2005 (I) and September 2006 (II) at CESAR
(Cabauw Experimental Site for Atmospheric Research) in Cabauw, the Netherlands (52°N,5°E).
Measurements of NO2, O3 and Aerosols from various platforms by means of different measurement methods.
Results are subject to intercomparison studies between instruments and validation of OMI and SCIAMACHY satellite data.
Total and tropospheric NO2 (SCIAMACHY, OMI), campaign organisation (KNMI), NO2 LIDAR profiles,
insitu NO2 monitor (RIVM), MAXDOAS measurements (BIRA, IUP Bremen, IUP Heidelberg)
MAXDOAS measurements (UV-vis)
Figure: Cabauw
Experimental Site
MAXDOAS intercomparisons and satellite validation
DOAS: Differential Optical Absorption Spectroscopy
Comparison between MAXDOAS results from Bremen (Vis
• Detection of trace gases via their characteristic spectral absorption features
• Description of broad-band structures (scattering, instrumental effects) by a polynomial
• Derivation from Lambert-Beer Absorption Law:
D
I
intensity affected by atmospheric interactions
Io
p
ln  s i ' SCi  a p 
I0
intensity not/less affected by atmosphere
I
i
p 0
s’
absorption cross section (differential part)
SCi
slant column (the concentration of the respective absorber integrated along the light path)
D
p polynomial of degree D
a

 p
instrument), BIRA and Heidelberg shows good consistency
between the different instruments.
• Correlation = 0.85 (2006, Bremen-BIRA)
• Correlation = 0.92 (2005, Bremen-BIRA)
• Correlation = 0.91 (2005, Heidelberg-BIRA)
Remaining deviations due to differences in: time of measurement,
viewing directions, reference absorption cross sections, AMF
assumptions.


p 0
Multi-Axis:
Scattered sun light from various viewing angles (zenith-sky and elevation angles from 0°-30°) is
measured
Lower viewing angles: light path through the troposphere increases  measurements get more
sensitive to tropospheric trace gases like NO2.
Calculation of NO2 vertical columns (VC) via geometrical air mass factor (AMF).
Comparison of the different viewing angles: profile information can be retrieved.
For DANDELIONS-II, two Bremen MAXDOAS instruments were taking measurements in the visible
and the UV wavelength ranges. NO2 is retrieved in the fitting windows:
UV: 345 – 370 nm
Vis: 450 – 497 nm
Figures: Correlation plots for 2005, left: BIRA-Bremen, right: BIRA-Heidelberg
Figures: Results from 2006. top: timeseries of
Bremen and BIRA data, bottom: correlation plot
for same results.
Validation of satellite results:
NO2 retrieved from SCIAMACHY (Bremen data product) is compared
to ground-based DOAS results from the Bremen Vis instrument.
• MAXDOAS data: taken at Cabauw in SW viewing direction
• SCIAMACHY data: from within 50 km (or 200 km) around Cabauw
Correlation: R = 0.72
Including data from distances up to 200 km decreases R to 0.55.
Limitations:
• SCIA pixel 30x60 km²
Ground-based: point-measurement
• different time of measurement (interpolation)
• different viewing geometry  different aerosol influence
Figure (left): time series for the comparison of tropospheric NO2 from the UV and vis instruments for Sep
2006. (right): correlation plot for the same data set.
The results from the two instruments agree quite well with a correlation of 0.89, the UV instrument
showing slightly higher NO2 values than the Vis instrument. The differences show the influence of the
retrieval settings and assumptions. In the following, results from the Vis instrument are used.
NO2 profiles
•
•
•
•
•
From MAXDOAS measurements, NO2 profile information is retrieved with
BREAM (Bremian Advanced MAXDOAS Retrieval Algorithm):
for a chosen time period, the NO2 profile at the measurement site is calculated
measured slant columns from the different MAXDOAS viewing angles are used
includes radiative transfer calculations from the SCIATRAN code
for calculations of the aerosol amount, the retrieved O4 amount is used
comparison of retrieved surface concentrations with in situ NO2 monitor is possible
Figure (top): time series of MAXDOAS and SCIAMACHY tropospheric vertical
columns of NO2 for DANDELIONS-II.
(bottom): scatterplot for both campaigns in 2005 and 2006. The correlation of 0.72
shows good agreement, differences can be understood from above reasoning. The
SCIAMACHY data points from distances >50km show larger variations.
HCHO at Cabauw
Figure (below): time series of NO2 and
HCHO for the DANDELIONS-II campaign.
Figure
(below):
Surface
concentration and mixing
ratio of NO2 from MAXDOAS
and in situ measurements
Figure (above): Daily variation of
the NO2 profile on Sep 13. The
ground layer with the highest NO2
values increases towards midday.
Figure (above): NO2 profiles on Sep
13 for different times. The highest
values are found close to the ground
rapidly decreasing with height as
expected from the strong split-up in
NO2 slant columns with viewing angle.
Figure (right):
typical fit
result for
HCHO on
Sep 13 in
Cabauw.
From the MAXDOAS measurements, also tropospheric
formaldehyde (HCHO) columns are retrieved. Comparison of
HCHO and NO2 can be used as a measure for air pollution
sources. For anthropogenic sources, tropospheric NO2 prevails. In
Cabauw, varying situations occur. On some days, HCHO values
exceed NO2, on others the situation is vice versa. This clearly
indicates different sources for the two gases. In the mean, for
September 2006, tropospheric amounts of both trace gases are
similar (with vertical columns of 1.3.1016 molec/cm2).
Figures (above): Comparison of HCHO (left) and NO2 (right) slant columns at
Cabauw on Sep 13 from MAXDOAS measurements. Both trace gases show
clear splitting-up of the slant column values for the different viewing angles (30°
and 0° to 16° scans), typical for tropospheric trace gases. The splitting is less for
HCHO, so the profile is less pronounced towards the surface.
Conclusions
Acknowledgements
• Measurements of tropospheric NO2 from different MAXDOAS instruments at the DANDELIONS
campaigns show good intercomparison results and were used for validation of SCIAMACHY data.
• NO2 profiles show highest values close to the ground and allow comparison with measurements
from a ground-based in situ NO2 monitor.
• Formaldehyde column amounts lie in the same range as the NO2 values in September 2006. On
some days NO2 prevails, on others HCHO, clearly showing different sources.
• Further comparisons of MAXDOAS results with NO2 LIDAR profiles and in situ measurements at
200 m altitude will follow shortly.
• Collaboration with all DANDELIONS participants is gratefully acknowledged.
• Parts of the project have been funded by the University of Bremen and the ACCENT network.
Selected References
• F. Wittrock, H. Oetjen, A. Richter, S. Fietkau, T. Medeke, A. Rozanov, and J. P. Burrows: MAX-DOAS measurements of
atmospheric trace gases in Ny-Ålesund - Radiative transfer studies and their application, Atmos. Chem. Phys. 4, 955-966, 2004.
• A. Heckel, A. Richter, T. Tarsu, F. Wittrock, C. Hak, I. Pundt, W. Junkermann, and J. P. Burrows: MAX-DOAS measurements of
formaldehyde in the Po-Valley, Atmos. Chem. Phys. Discuss. 4, 1151–1180, 2004.
• A. Rozanov, V. V. Rozanov, and J. P. Burrows: A numerical radiative transfermodel for a spherical planetary atmosphere:
combined differential-integral approach involving the Picard iterative approximation, J. Quant. Spectrosc. Radiat. Transfer 69, 491,
2001.
• E. Brinksma et al.: NO2 and aerosol validation during the 2005 and 2006 DANDELIONS campaigns, JGR, to be published.
• Campaign website: http://www.knmi.nl/omi/research/validation/dandelions