MAXDOAS measurements from the DANDELIONS campaigns

1
MAXDOAS measurements from the DANDELIONS campaigns
DPG 2007 UP 8.6
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 4RIVM, National Institute for Public
Health and the Environment, Bilthoven, The
Netherlands 2BIRA, Belgian Institute for Space
Aeronomy, Brusseles, Belgium 5KNMI, Royal
Netherlands Meteorological Institute, De Bilt,
The Netherlands 3Institute of Environmental
Physics, University of Heidelberg, Germany 6Max
Planck Institute for Chemistry, Mainz,
Germany Email anja.schoenhardt_at_iup.physik.uni
-bremen.de
Introduction
DANDELIONS Dutch Aerosol and Nitrogen Dioxide
Experiments for Validation of OMI and
SCIAMACHY Campaign Information Validation
Campaign in Mai-July 2005 (I) and September 2006
(II) at CESAR (Cabauw Experimental Site for
Atmospheric Research) in Cabauw, the Netherlands
(52N,5E). Main Objectives 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. Participants in NO2
measurements Total and tropospheric NO2
(SCIAMACHY, OMI), campaign organisation (KNMI),
NO2 LIDAR profiles, insitu NO2 monitor (RIVM),
MAXDOAS measurements (BIRA, IUP Bremen, IUP
Heidelberg)
Figure Cabauw Experimental Site
MAXDOAS measurements (UV-vis)
MAXDOAS intercomparisons and satellite validation

• DOAS Differential Optical Absorption
  Spectroscopy
• 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
• I intensity affected by atmospheric
  interactions
• I0 intensity not/less affected by atmosphere
• s absorption cross section (differential part)
• SCi slant column (the concentration of the
  respective absorber integrated along the light
  path)
• polynomial of degree D
• 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.

• Comparison between MAXDOAS results from Bremen
  (Vis 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.

Figures Results from 2006. top timeseries of
Bremen and BIRA data, bottom correlation plot
for same results.
Figures Correlation plots for 2005, left
BIRA-Bremen, right BIRA-Heidelberg
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

• 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.
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 gt50km show larger
variations.
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.
HCHO at Cabauw
NO2 profiles
From MAXDOAS measurements, NO2 profile
information is retrieved with BREAM (Bremian
Advanced MAXDOAS Retrieval Algorithm)
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).

• 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 (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 (right) typical fit result for HCHO on
Sep 13 in Cabauw.
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.
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.
Figure (above) Daily variation of the NO2
profile on Sep 13. The ground layer with the
highest NO2 values increases towards midday.
Acknowledgements
Conclusions

• 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,
  11511180, 2004.
• A. Rozanov, V. V. Rozanov, and J. P. Burrows A
  numerical radiative transfermodel for a spherical
  planetary atmosphere combined differential-integr
  al 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