1. A comparison study of stratospheric NO2 profiles among ground-based zenith sky DOAS, SCIAMACHY limb measurements and SAOZ balloon-measurements over Kiruna, Sweden
Myojeong Gu1, Carl-Fredrick Enell2, Florence Goutail3, François Hendrick4,
Ulrich Platt5, Jean-Pierre Pommereau3, Janis Pukite1, Uwe Raffalski6,
Michel Van Roozendael4, Thomas Wagner1
(1) Max-Planck Institute for Chemistry, Mainz, Germany
(2) EISCAT Scientific Association, Kiruna, Sweden
(3) LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales
(4) Institut d'Aéronomie Spatiale de Belgique (IASB-BIRA), Brussels, Belgium
(5) Institute for Environmental Physics, University of Heidelberg, Heidelberg, Germany
(6) Swedish Institute of Space Physics, Kiruna, Sweden
Stratospheric NO2
Measurements
Retrieval methods
Results
In this talk, I am going to talk about the comparison study of NO2 profiles among ground-based zenith sky DOAS, SCIMACHY limb measurement and SAOZ balloon measurement over Kiruna. 1

2. Introduction: Stratospheric NO2
Influence the ozone chemistry : depending on the altitude.
Middle and upper stratosphere (25 – 40 km): NOx destruction of ozone
NO +O3 → NO2 +O2
NO2 + O → NO +O2
NO2 +hv → NO + O [Crutzen, 1970]
Below 25km: acting as a buffer against halogen-catalyzed O3 loss through the formation of reservoir species (ClONO2, BrONO2).
ClO + NO2 → ClONO2
BrO + NO2 → BrONO2
Stratospheric NO2 plays an important role in the ozone chemistry and its effect depends on the altitude.
In the middle and upper stratosphere, NOx is a main source of destruction of ozone.
The reaction of NO2 with O3 occurs to form the nitrate radical, and it photolysis.
And below 25km, lower stratosphere, NO2 interferes with ClOx and BrO cycles..
These ClONO2, BrONO2 are reservoir species and take clo and bro out of their o3 destruction cycles.

3. Introduction : Ground-based zenith sky DOAS
observation of scattered sun light at zenith angles
Zenith sky DOAS :
Records spectra of scattered sunlight in zenith direction.
Observation of stratospheric trace gases: during each twilight : Increasing sensitivity of measurement as a result of a long light path in stratosphere.
Measurement site : Kiruna, Sweden: 68.84°N, 20.41°E
Good place to study the polar stratospheric chemistry.
Located in the arctic circle and is often situated under the polar vortex. Mountain wave induced Polar Stratospheric Clouds (PSCs) develop.
To investigate the NO2 vertical distribution, in this study we used ground-based zenith sky DOAS measurement.
This instrument records scattered sunlight in zenith direction.
The advantage of this measurement is that we can observe the stratospheric trace gases during each twilight.
Because during twilight time, the sensitivity of measurement increases as a results of a long light path in stratosphere.
This instrument has been installed at Kiruna since 1996 December, Sweden. This measurement site belongs to arctic circle. It is good place to study of the polar stratospheric chemistry.
It is often situated under the polar vortex and PSC.
Installation of Zenith Sky DOAS
Measurement starts: December of 1996 and since then performed automatic measurements up to now.
Wavelength range: 300nm to 400nm

4. NDACC Climatology AMFs LUT
Data Scheme
Zenith sky DOAS meas.
SCIAMACHY limb meas.
SAOZ balloon
NDACC Climatology AMFs LUT
developed by CNES
Langley plot
method
dSCDs
dSCDs
2-D Retrieval
[A] Profile
IASB-BIRA algorithm
NO2 profile
Ground-based profile
profile
Smoothed profile
AvK, a prior
In this work, we compared the profile and the partial column using three data set.
At first, we produce VCDs by applying the Langley plot method with the value of climatology AMFs to the DSCD from zenith sky DOAS.
Using the profiling algorithm based on OEM method, we retrieval a zenith sky DOAS profile.
Moreover, by integrating these profile, we obtain the partial column.
Other NO2 vertical profiles are retrieved from SCIAMACHY measurement in limb geometry using 2-D retrieval approach.
SCIAMACHY profiles are convoluted using AvK and aprior information from the zenith sky DOAS. Due to the difference in vertical resolution, the SCIAMACHY profiles should be degraded on the resolution of the zenith sky profiles. Also by integrating these profile from 12-42km, we obtain the partial column.
Last one is SAOZ balloon measurements developed by CNES, it provides NO2 vertical profiles.
[B] Partial column
VCDs
Integrating profile
Integrating
12 – 42 km

5. Data Scheme DOAS settings: Wavelength range: 356-392 nm
Cross sections:
NO2 (Vandaele et al.1998, 220K)
O3 (Bogumil et al.2003, 223K, 243K), O4(Greenblatt et al. 1990), Ring
Daily based reference spectrum (for each twilight, the spectrum closest to SZA 80°)
Zenith sky DOAS meas.
IASB-BIRA NO2 profiling algorithm
[Hendrick et al., 2004]
Mean scattering height depends on SZA
Based on the Optimal Estimation Method
Forward model (RTM + Photochemical model)
SCIAMACHY NO2 profiles are retrieved from limb geometry measurement.
Altitude range : 12 – 42 km
Using 2-D retrieval approach [Pukite et al., 2010]
Coincidence criteria for comparison :
SCIAMACHY observations on same day. Closest coincidence event within 1000km is chosen.
SCIAMACHY limb meas.
SYSTEME D'ANALYSE PAR OBSERVATION ZENITHALE (SAOZ)
SAOZ balloon gondola using UV-Visible spectrometer [SAOZ team]
NO2 spectral window: 450 – 526nm
This study, all balloon measurements were launched at Kiruna.
Coincidence criteria for comparison: SAOZ balloon measurement on same day. Using the evening ascent measurement.
SAOZ balloon

6. NDACC Climatology AMFs LUT
Langley plot methods
2013, Day Number: 145
Zenith sky DOAS meas.
dSCDs
VCDs
Langley plot
method
NDACC Climatology AMFs LUT
For the retrieval of VCDs in this study we used Langley plot methods.
To get a VCDs, plotting the DSCD as a function of AMF. Here, AMF we used NDACC climatology AMFs. Then, the slope and ordinate of this curve refer to VCDs for NO2 and SCD ref, respcectivel. Here, we attempt to use daily reference spectra, I got several SCD ref.
Rearanging this plot, finally we get the VCDs.
Because, for high SZA, the NO2 conc. are higher than those for the lower SZA. -> it means that the slope of this langley plot overestimated due to the photochemistry.
Remark!!
Langley plot will be affect by Photochemistry.
Tends to overestimate true SCD.
Plotting the DSCD(θ) as a function of AMF(θ) :
The slope and ordinate of the curve refer to VCDs for NO2 and SCDref, respectively.
SCDref : Actual amount of NO2 in the reference spectrum
!! Langley plot will be affect by Photochemistry. Tends to overestimate true VCD.

7. Results (1): Profiles
Now, let’s move on to results, first I will show the profile comparisons.

8. Measurement response 2005/Apr/21 @AM 2005/Apr/25 @PM SCIAMACHY
Zenith sky DOAS
Before showing our main results, I first show you the measurement response graphs.
These lines indicate sum of the rows of the averaging kernels. Red and blue lines indicate DOAS and SCIAMACHY, respectively.
Sensitivity from km differ AM and PM.
These red and blue line indicates sum of the rows of the averaging kernels.
Meas. responses in AM and PM: similar to each other
High sensitivity: 13 km to 38 km (SCIAMACHY), 18 km to 45 km (Zenith sky DOAS)

9. Seasonal mean profile (2002 – 2006)
Spring AM (#112)
Spring PM (#88)
Summer AM (#80)
Summer PM (#87)
NO2 conc. [molec/cm2]
Spring : March-May
Summer: Mid Jun - Aug
Retrieved from zenith sky DOAS (blue)
Unsmoothed SCIA profile (black)
Smoothed SCIA profile (red)
a prior (grey)
Error bar: standard deviation
Smoothed profile
Xsmoothed_scia=Xa+A(Xscia– Xa)
Relative difference=
𝑆𝑚𝑜𝑜𝑡ℎ𝑒𝑑 𝑆𝐶𝐼𝐴−𝑧𝑒𝑛𝑖𝑡ℎ 𝑠𝑘𝑦 𝑧𝑒𝑛𝑖𝑡ℎ 𝑠𝑘𝑦 ×100
Let‘s move on the seasonal mean profile comparison.
These graphs show the mean profile in spring and summer from 2002 to 2006.
Each graph includes 4 profiles: Retrieved DOAS, unsmoothed and smoothed SICA profile, and aprior.
Here, we convolued SCIA profilie using zenith sky DOAS information.
Rel. Diff: Summer data show similar for AM and PM. It is related with polar day. There are no different between Meas.AM and PM.

10. Comparison of zenith sky DOAS profile and SCIAMACHY limb
profile : Monthly mean profile (2002 –
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
(#40)
(#40)
(#40)
(#40)
(#40)
(#49)
(#49)
(#49)
(#49)
(#49)
(#31)
(#31)
(#31)
(#31)
Error bars:
standard deviation
(#32)
(#32)
(#37)
(#37)
(#37)
(#19)
(#19)
- Good agreement
Small rel. diff
20 – 30 km: seasonal variation
Let’s look at, in detail, the monthly results.
These nine graphs represent the means and the relative differences from February to October. (here NDJ-> polar night, no data or statistically poor.
Each graph includes same as previous figure, for the individual month.
X and y axis mean no2 columns and altitude, respectively, and those indicate coincident events.
You can see a good agreement between DOAS and SCAI profiles. The smallest relative difference between them is below 10 percent.
As shown in results at from 20km to 30km, the seasonal variation is clearly observed.
You can also find that unsmoothed profiles below this altitude are much smaller than those in high altitude.
August(how can I explain?): we have also recognize that At the moment, we have no clear expiation. This is ongoing research.
(#18)
(#14)
(#24)
𝑆𝑚𝑜𝑜𝑡ℎ𝑒𝑑 𝑆𝐶𝐼𝐴−𝑧𝑒𝑛𝑖𝑡ℎ 𝑠𝑘𝑦 𝑧𝑒𝑛𝑖𝑡ℎ 𝑠𝑘𝑦 ×100

11. Comparison of zenith sky DOAS profile and SCIAMACHY limb
profile : Monthly mean profile (2002 –
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
(#42)
(#43)
(#19)
Error bars:
standard deviation
(#26)
(#30)
(#15)
- Good agreement
- Similar to
- Rel. diff: larger deviation
Now, go on to the monthly mean profiles measured at PM.
These graphs seem to be very similar to the graphs at AM in the previous slide, such that peak points in 20-30km show seasonal variation.
Rel.diff between DOAS and SCIA profile products show larger deviation.
We recognize quite large difference, still in the it seems be systematic. At the moment, we have no clear explanation.
Will be interesting for us further investigation.
Small deviation.. In the 20-25km
(#11)
(#6)
(#22)
𝑆𝑚𝑜𝑜𝑡ℎ𝑒𝑑 𝑆𝐶𝐼𝐴−𝑧𝑒𝑛𝑖𝑡ℎ 𝑠𝑘𝑦 𝑧𝑒𝑛𝑖𝑡ℎ 𝑠𝑘𝑦 ×100

12. Comparison of zenith sky DOAS and SAOZ balloon measurement
Zenith sky DOAS (blue)
SAOZ balloon (red)
Smoothed SAOZ balloon (magenta)
Now, we go on to the SAOZ balloon measurement and DOAS profile.
In this work, we show3 coincident events for 2spring coditions and 1 summer event.
The comparison between DOAS profiles and SAOZ measurements show a good agreement regarding the magnitude and the peak altitude.
It should, however, be noted that no perfect agreement can be expected because of the non-coincidence of both measurements and might be influenced by meteorological effect (e.g. polar vortex season during spring period)
Overall similar pattern regarding the magnitude and peak altitude.
However, no perfect agreement can be expected.→ non-coincidence of both measurement and influenced by metrological effect.

13. Potential vorticity on the isentropic surface of 475K
Sun position
Balloon trajectory
75°N
72°N
69°N
66°N
63°N
60°N
5°E
10°E
15°E
20°E
25°E
30°E h
Zenith sky DOAS
SAOZ balloon
Smoothed SAOZ balloon
If you look at the potential vorticity on the isentropic surface of 475K map.
Actually, 1997 March 20 was inside of polar vortex over Kiruna.
This box indicate Kiruna site and green one shows balloon trajectory and magenta show SAA.
Here is edge of polar vortex and did not probe same air mass.
Including line of sight.
End of March.. That is true,, this is already end of March..
PSC disperse already March..
SAA≈80°
SZA≈88°
16:00 UTC
[ECMWF]

14. Results (2): Partial columns
Next we move on the partial columns comparison.

15. Comparison of NO2 partial columns @ AM
2005
2006
NO2 column [molec/cm2]
Relative diff. [%]
Here, we show time series of NO2 columns and relative differences.
Due to the instrument’s technical problem, there are small number of events
So, here we focused on 2005 and 2006.
Each graph contains four data of NO2 columns measured at AM. The green one is obtained by integrating the unsmoothed SCIAMACHY profiles, the blue one is the integral of the smoothed SCIA. Integral values of DOAS profiles are represented by red circles, and VCDs by the Langley plot method are shown by sky-blue circles.
X and y axes indicate the monthly based time and NO2 partial columns, respectively.
Good agreement, Especially, results by the profile inversion shows good agreement with each other.
Large variations of spring data in both graphs are also observed.
At the beginning of the year, VCDs are small. Because of that rel.diff quite large at the beginning of the year.
But the later in the year, the agreement is much better because of the higher values.
smoothed SCIA – DOAS/DOAS [%]
Langley plot method-DOAS/DOAS[%]
- Good temporal agreement
- Spring period: large variations
- At the beginning of the year, VCDs (Langley methods) are small.← Rel. diff. large

16. Comparison of NO2 partial columns @ PM
2005
2006
NO2 column [molec/cm2]
Relative diff. [%]
Now, go on to NO2 partial columns measured at PM.
It is quite similar results show systematic difference.
As quite similar results as previious slide. Especially, Langley plot results shown by sky-blue circles are larger than other profile inversion groups.
I already mentioned before, Langley plot methods VCD tends to be overestimated
For higher SZA, the NO2 concentrations are higher than those for the lower SZA because of the photochemistry, which means that the slope of the Langley plot would be overestimated due to the photochemistry.
smoothed SCIA – DOAS/DOAS [%]
Langley plot method-DOAS/DOAS[%]
- Langley plot results: larger than other profile inversion groups.
→ Langley plot methods would be overestimated due to the photochemistry.

17. Summary
In this study, we retrieve stratospheric NO2 profile measured from ground- based zenith sky DOAS using IASB-BIRA profiling algorithm and compare it with SCIAMACHY limb measurements and Balloon measurements.
Results from the retrieval NO2 profile and partial columns agree generally well SCIAMACHY and SAOZ balloon measurements.
Outlook:
Need for a new criterion to find coincident events.
In this work, we used the location of the Kiruna instrument to calculate the distance to the SCIAMACHY measurement.
In the near future, we will use the air volume for reaching a measurement most sensitive (several hundreds kilometer towards the sun to calculate the distance to the other measurements → 2-D box AMFs)
To sum up,
Using ground-based zenith sky DOAS measurements at Kiruna, we retrieved NO2 profile apply the BIRA algorithm.
Here, we showed NO2 profile and parcial columns have been compared with SCIA and SAOZ.

18. Thank you for your attention!

19. NDACC Climatology AMF LUTs
latitude
(85°S ~ 85°N) step 10°
period
Jan. to Dec. step 1 month
Sunrise (sr) and Sunset (ss)
Altitude range
20 ~ 60 km
Wavelength
350 to 550 nm step 40nm
Surface albedo
0 and 1
Altitude of the station
0 and 4 km
SZA
10, 30, 50, 70, 80, 82.5, 85, 86, 87, 88, 89, 90, 91, and 92°

20. 1997. 03. 20. 18h PV 475K Tropopause 75°N 72°N 69°N 66°N 63°N 60°N