University of Bremen IUP DOAS





IUP Bremen DOAS Blog

Sitting in front of building NW1

Janos Ritter, 20.12.2022

I was probably not the first student who took measurements in front of the University building NW1 for his bachelor thesis, but I believe it was still a funny image seeing me sitting in front of the building in a camping chair with an Avantes DOAS device. For my bachelor thesis I was performing and comparing DOAS measurements of NO2 at different altitudes. The idea was to have two identical devices, one placed on top of the building where most permanently installed devices of the DOAS group are located, and another one which is repeatedly carried up to the roof and down to the ground. Since the results of DOAS measurements are based on the light path through the atmosphere, the measurement from the ground should show larger NO2 columns than those from the roof. The comparison of both devices should allow me to calculate the amount of NO2 in the surface layer. It is important to note that the devices are not directly compared to each other. Rather the device on the roof is used as a baseline to correct for possible time dependent offsets, and the other device is then compared to itself. This approach corrects for small differences between the devices and also makes the results independent from the chosen background intensity. Since one single data set is not really statistically meaningful, I had to take the device up and down several times a day on a total of 14 days. On some hot summer days this was really exhausting, especially because the IUP building has one of the worst elevators in Bremen which broke down 6 times during the 4 months I was writing my thesis, so I had to walk up 148 steps of stairs.


a) Measurement setup on the roof of the NW1 building. b) Measurement setup on the ground in formt of the NW1 building.

Taking the device up and down was basically all I had to do. After applying a few settings in the morning, the Avantes devices perform the measurements completely automatically. In the end I was just sitting next to the measuring device protecting it from theft and anything else that might happen, and I was prepared to answer the question what I was doing there in my chair several times a day for a bunch of different people, including several professors, fellow students and some people who I think just randomly walked by and thought I could use some company.

I am happy, that I had the change to work on a bachelor thesis where I could perform my own measurements. It was an interesting experience to for the first time build my own measuring setup and specially to improve different flaws I only realized after taking my first few sets of measurements. Of course the flaws I noticed during my measurements led to the fact, that I had to discard several data sets, but in the end this process allowed me to better understand my experiment, the devices and my results. My final results are shown in the following figure and are also compared to modelling values of the CAMS reginal model ensemble. The results show positive values with a magnitude of 1x1015 molec cm-2 which is in line with the expectations. One thing that stands out immediately are the large uncertainties. These are caused by several steps of error propagation and the high fluctuation of the relatively simple Avantes devices I used.


Slant column differences between ground and roof top as a function of local time.

The Avantes devices are highly sensitive towards changes in temperature and therefore are not perfectly suited for these kinds of measurements. The sensitivity and the capabilities of the Avantes devices is one of the mayor conclusions from my bachelor thesis. If I would ever repeat my measurements, the used Avantes devices would give me some room for improvements. They were chosen for their simplicity and low weight which made it easy to carry them up and down the stairs, but since one of the device was constantly placed on top of the building this device could easily be replaced by a more complex, temperature controlled and more precise device of the DOAS group which would create a much more solid baseline for the evaluation. In addition a temperature controlled Avantes device would improve the accuracy even further.

An ERASMUS+ summer in Bremen

Chivintar Amenty, 27.10.2022

Spending a summer in Bremen while learning about satellites can take as many dimensions as a NetCDF file; unlimited. Especially when the place you land is the IUP DOAS _group_. My lucky Erasmus+ internship had me observing the 2021 wildfires in the Mediterranean with TROPOMI, with an ambition to estimate the NOx emissions that emanated from them. Of course to do that one must use the shell prompt to connect with the remote server, to find, download, view and manipulate the data, think the physics and finally do the math. We can think the verbs in the above sentence as completely different groups in that NetCDF file, each with its own multiple variables, that had to be thoroughly studied. For the _shell_connect_ group for example, we can imagine a couple, such as _re-learn_terminal_commands_ or, _what_is_secure_transfer_protocol_. In the _view_data_ group we would see _be_sure_to_create_stable_environments_ attributes and so on. Of course, learning the structures of such file formats was just the start.

Another group in our file was the _laboratory_. It contained the awesome equipment and materials that I got to see. For example, the spectrometers (where I naturally could not help but try the sunglasses to see live the cutoff of the sun’s UV) and the HgCd lamp that we used to calibrate them (while it took me a few seconds to realize why the photochromic glasses don’t turn brown, but the lamp emits in the UV...!). I must also mention the big cool iDOAS instrument, which a few weeks later was on its mission, flying and measuring trace gases, on a measuring campaign in Northern Italy.


Some plots from the _laboratory_ group. From left: the iDOAS, the spectrometers under a nice clear sky, the turned on HgCd lamp (shall not see with naked eyes).

The campaigns! The campaigns that went on this summer within the DOAS group were fascinating to follow, similarly to the episodes of your favorite show. The heroes (researchers) of the story would face a challenging challenge, overcome it with grace, and wait (for not so long) for the next challenge to arise. Naturally, they would overcome this too. Undoubtedly this experience sounds more than appealing to me, and has also inspired me in a non trivial fashion.

The daily lunches and the exceptional dinners with the DOAS group were no less interesting. Lunch time was many times the highlight of the day, the moment where a simple comment from a colleague would clarify a _thing_ I was baffling with the whole day. No wonder now, why one can see many long tables in the Mensa. Further combining the ice cream on the way back to the office, the discussions could drive the tangent and become particularly fun.

In 2022 Bremen experienced an unusually hot and clear-sky summer, thus I had many chances to explore the nature around, with, coming from Crete, usual for me temperatures. My favourite place became the Bürgerpark, but the hardest thing - still - is to pronounce its name. Connecting to my office from my neighbourhood was everyday a very pleasant bike ride, through the Parkallee – maybe an additional _own_a_good_bike_lock_ attribute should be inserted here as well!

Learning about remote sensing and satellite data in the IUP is definitely an ultimate experience. I am now looking forward to the day when, as a guest in Bremen, will invite the colleagues to a DOAS dinner again in a traditional German restaurant, possibly with Italian cuisine.


Left: The clear sky offered some spectacular evenings in the office. Right: On a DOAS dinner event.

Combining the weekly workout with DOAS measurements

Simon Bittner, 19.08.2022

For the experimental part of my Master thesis, I thought of the idea of combining a hobby of mine with scientific measurements. In principle, it was a good idea: Traveling by bike on days with good weather and at the same time collecting data with an Avantes spectrometer for the estimation of airborne NOX emissions via differential optical absorption spectroscopy (DOAS). I only missed one aspect. One needs a lot of data for it to be statistically valid. So I ended up measuring on seven days with an average driving distance of approximately 70 km per day. Note that there are only so many sunny days in Germany. Therefore, one better not does breaks.

My setup is shown in the picture. The measurement computer and the Avantes instrument are carefully surrounded by my wardrobe inside of the pannier. The pannier on the other side served only one purpose: Balancing the weight of the measurement setup. In total, I was driving with approximately 14 kg of extra luggage. Additionally, I installed a GPS receiver right next to  the telescope opening of the spectrometer and a lamp towards the front, which, in the ideal case, indicated that everything was functioning well.


The setup of the bike DOAS instrument.

The original idea was to quantify the NOX emissions of the airport Bremen. But before that, I tested my setup for the waste incineration facility in Findorff, Bremen which is operated by SWB. The idea was to surround the source and then subtract the outgoing flux from the incoming flux. Mathematically, it can be described via the divergence law of Gauss.

Depicted below is one exemplary circle around the waste incineration plant. One finds the plume, where one would suspect it: Downwind of the chimney. The idea is well visualized in that picture. On the upwind side, the vertical column densities of NO2 are negligible, and on the downwind side, the signal is in general higher with a strong signal from the plume. So it can be concluded that the origin of the signal is inside the encircled area.


An example result of a round of bike DOAS measurements around the waste incineration facility in Bremen.

Calculating the flux of NO2 with the above-sketched method leads to the results depicted below. In the end, I evaluated 13 rounds. It is visible, that the values vary quite a lot. This has several reasons:

  1. unstable atmospheric conditions
  2. the wind field from the database is not accurate (I used data from teh DWD station located at airport Bremen)
  3. different components in the fuel/waste mixture
I took all the measurements mainly during June on weekdays.


Overview on the emission estimates derived from several days of bike DOAS measurements around the incineration plant.

After converting the flux of NO2 to NOX, one retrieves an emission signal comparable to the published values of 2020 from SWB in the Pollutant Release and Transfer Register. The method was working!

Next stop: Airport Bremen. In the beginning, I took the measurements alone, but after noticing the awfully long time it took to complete a single measurement, I recruited a volunteer and we duplicated the setup. Unfortunately, this time the airborne emissions were way more difficult to quantify than expected, due to the location of the airport. It is further embedded into the city and parts of the closest route were covered with trees. Furthermore, it is not a distinct point source, and as a consequence, no correction of the evaluated rounds due to the wind direction could be applied. The mean emission is significantly lower and considering one standard deviation includes zero.

Currently, I am resting my legs on the couch and working on modeling the atmosphere on the specific dates, where I measured with my bike.

All in all, I enjoyed being outdoors and taking measurements, even though I would suggest an electric bike for follow-up campaigns.


The author before starting on his first measurement trip.

Retrieving NO2 profiles from MAX-DOAS measurements in the Po valley

Paolo Pettinari, CNR-ISAC, 07.04.2022

In the frame of the IDEAS-QA4EO project “Sviluppo delle Infrastrutture e Programma Biennale degli Interventi del Consiglio Nazionale delle Ricerche Potenziamento Infrastrutturale: progetti di ricerca strategici per l’ente. Progetto 32 – ASSE NORD Pianura Padana Mt. Cimone, Bologna, San Pietro Capofiume”, the Italian research institute CNR-ISAC bought a new MAX-DOAS instrument called SkySpec2D. Since no MAX-DOAS measurements, able to meet the FRM4DOAS standard requirements, were present in the Po Valley, the purpose was to fill this gap in one of the most polluted regions in Europe. After two inter-calibration campaigns, organized to evaluate the SkySpec2D performances, my colleagues, Elisa Castelli and Enzo Papandrea, and I installed the MAX-DOAS instrument at the measurement site located in San Pietro Capofiume, in the middle of the Po Valley, on 1st October 2021 (see image below).

We started our work retrieving the NO2 total Vertical Column Densities (VCDs) from zenith-sky spectra because it didn’t require a complex retrieval algorithm that we had not yet developed. However, I performed a further step during my period abroad. On 10th January, I moved to Bremen, where I spent three months of my PhD and worked with the DOAS group of the Institute of Environmental Physics at the University of Bremen, under the supervision of Dr Andreas Richter. Here, I started to analyze the SkySpec2D off-axis measurements to retrieve NO2 vertical profiles.


Paolo Pettinari in San Pietro Capofiume (Italy) during the installation of a SkySpec2D MAX-DOAS instrument.

In the beginning, I performed a characterization of the MAX-DOAS instrument. Then, I optimized the measurement strategy and checked the instrument’s pointing stability and the best viewing directions. I then applied the BOREAS algorithm, developed by Tim Bösch at IUP Bremen, to the NO2 Slant Columns Densities (SCDs) estimated from the DOAS fit to retrieve NO2 vertical profiles in the Po Valley. An example of the retrieved NO2 profiles is shown in the figure below on the left.

The last step of my stay in Bremen was focused on using the retrieved profiles to validate the NO2 tropospheric columns measured by TROPOMI onboard S5P (results in the figure below on the right).


NO2 vertical profiles in the Po Valley as retrieved by BOREAS from MAX-DOAS elevation scans in the 120° azimuth direction for 14th December 2021 (on the left). Comparison between MAX-DOAS and TROPOMI NO2 tropospheric VCDs for October 202 (on the right).

Even though everything was new for me, it’s been quite easy to achieve the expected results due to both important suggestions, the consequence of a strong DOAS experience at IUP, and the group’s positive mood that made me feel part of them soon.

Maintenance stay at the research station in Ny-Ålesund (14.3.-28.3.2022)

Lisa Behrens and Tim Bösch, 06.04.2022

About the research station

Ny-Ålesund is the northernmost year-round research station in the world. The village is located at 78°55‘N, 11°55‘E in the bay of the Kongsfjorden. Only 30 to 35 people are living permanently at the station. In summer, the population increases up to 114 due to high research activities. Currently, 19 institutions from 11 countries are represented at the station. Ny-Ålesund was established by a private coal mining company called “Kings Bay Kull Compani AS“ in 1917. Between 1917 and 1929, Ny-Ålesund was also a starting point for several expeditions attempting to reach the North Pole. In 1933, the Norwegian state took over the ownership of the company. The main interest was establishing the village as a tourist destination and its usage as a fishing port. The coal mining activities resumed between 1945 and 1962. Several mining accidents occurred, with the worst in 1962 killing 21 miners and leading to the shutdown of the mining activities. In 1967, the transition to a research station was initiated. Kings Bay still provides the research infrastructure for a broad research community.


The village Ny-Ålesund with the Zeppelin Mountain in the background. View from the harbour. (Photo: Lisa Behrens).

How to get to Ny-Ålesund?

Getting to Ny-Ålesund is not that easy. One possibility is a cruise vessel during summer, which tourists typically choose. Another possibility is an aeroplane. We first took an aircraft to Longyearbyen, the capital of Spitsbergen, which included an overnight stay in Oslo. From Longyearbyen, a small plane to Ny-Ålesund is operated by Kings Bay twice per week (usually Monday and Thursday). The plane is a Dornier 228 (Do 228), being a twin-turboprop aircraft with space for 14 passengers + 2 pilots.

The schedule of these small planes depends strongly on the weather conditions. With high wind speeds, the aircraft cannot fly. This was the case for our flight to Ny-Ålesund, and we were delayed by a few hours.

Scientific work

The IUP Bremen operates a DOAS instrument in Ny-Ålesund since 1995. The instrument is installed on the roof of the observatory building. The original focus was on stratospheric measurements in the arctic regions being influenced by the polar vortex, which is especially interesting for ozone chemistry. Another focus is on polar tropospheric halogen chemistry, particularly bromine chemistry. Depending on the meteorological conditions, events of ozone destruction can frequently be observed in relation to high bromine concentrations. Furthermore, pollution by nitrogen dioxide and sulphur dioxide from cruise vessels can be investigated. In April 2011, the current telescope with a pan-tilt-head and a two-channel spectrometer system was installed. This type of telescope allows measurements in various azimuth and elevation angles. Thus, the telescope moves the whole day in harsh weather conditions, leading to the need to replace some parts and cables from time to time. The replacement of the cables and light fibre was part of our activity.

On Tuesday, the 15.3.2022, a new temperature record was measured in Ny-Ålesund with -5.5°C, while temperatures of about -14°C would have been expected. These high temperatures were related to precipitation in terms of rain or freezing rain. After a few days, weather conditions improved a lot, and we had sunny weather with -18°C. Due to these rapidly changing weather conditions, we had to re-schedule our work. We replaced all cables leading through the window from the laboratory to the instrument on the roof, refurbished the telescope, and replaced the CCD of the visible spectrometer. Luckily, we finished our work in time. By the end of the second week, we waited for some clear sky days to let the instrument do some test measurements. This waiting gave us a bit of freedom to enjoy the beautiful environment of Svalbard!


The Observatory of AWIPEV, where the DOAS instrument is located (Photo: Tim Bösch).

Social life

Besides work, social life is essential in such a remote destination. Kings Bay operates a canteen serving food on weekdays at 7:30, 12:00, and 16:30 for one hour. On the weekend, they serve a delicious brunch, and on Saturday evening, there is a special dinner. All people are well-dressed (if possible), and it is the only meal where alcoholic drinks are allowed. Afterwards, the bar opens, and people can enjoy the beautiful view over the tundra with music and good company.

When leaving the village, a rifle is needed due to possible contact with polar bears. However, with such protection, nice trips can be made with skis, snowshoes, ski-doos or simply by hiking. All over Svalbard, there are small huts that can be used for a small rest or an overnight stay.

We did a ski tour to visit one of these huts and see the seals in the Kongsfjorden, which enjoyed the beautiful sunny weather and -18°C on a small island. Another trip led us to Corbel. This is a French station from 1963, located approximately 5 km away from Ny-Ålesund. You could enjoy the view over the fjord and the glaciers at this place.

On our last day, we could participate in a short round trip to the Engelskbukta, approximately 30 km away from Ny-Ålesund. It was a long trip with ski-doos, where we had to pass some iced rivers. We visited some huts on our way to the bay, saw several reindeers, and enjoyed the beautiful landscape. Close to Engelkbukta, we could see the whole “Prins Karls Forland”, an 80km long island belonging to Svalbard. This was an excellent example of the incredibly clear sky, which one can only experience in remote and unpolluted places like Ny-Ålesund.

Outside the village a rifle is needed (Photo: Lisa Behrens).
Seals in Kongsfjorden (Photo: Tim Bösch).
Corbel, French station, 5km away from Ny-Ålesund (Photo: Lisa Behrens).

SO287-CONNECT cruise onboard RV Sonne from Las Palmas (Gran Canary, Spain) to Guayaquil (Ecuador) (11.12.2021 - 11.01.2022)

Miriam Latsch, 05.04.2022

The SO287-CONNECT cruise of the research vessel (RV) Sonne departed Gran Canary in the western subtropical Atlantic Ocean on 11 December 2021. We sailed along the North Equatorial Current to the Sargasso Sea as the northernmost point of the voyage and crossed the Caribbean Sea. After an exciting transit through the Panama Canal, we entered the tropical Pacific Ocean, finally reaching the port city of Guayaquil in Ecuador on 11 January 2022, after 11,000 km of transit. Onboard the RV Sonne traveled 30 ship’s crew members and 39 scientists with a variety of research interests (e.g., biogeochemical, ecological, atmospheric). For example, the oceanographers investigated nutrients and many different chemicals of natural and anthropogenic origin from the water at various depths, as well as microplastics in the oceans.


Miriam Latsch and Tim Bösch below the two MAX-DOAS telescopes installed on Deck 10, measuring scattered sunlight in the atmosphere to determine concentrations of atmospheric trace gases (Photo: Tim Bösch).

We from the DOAS group at IUP Bremen measured atmospheric trace gases with our instruments on Deck 10, which is about 27 meters above the water surface (see picture above). Observations of scattered sunlight were carried out using an Avantes spectrometer in MAX-DOAS configuration and a MAX-DOAS system to analyze the amount of absorption of trace gases in the atmosphere, such as NO2, Ozone, and SO2. These gases are key parameters for air quality and are emitted by ships, for example. Furthermore, in situ measurements of NOx, SO2, CO, and Black Carbon were conducted to better determine the impact of different sources, e.g., passing ships.

Ship emissions have an impact on the environment and human health, and the aim of measurements of atmospheric pollutants during the SO287-CONNECT cruise was to monitor the contribution of ship emissions and long-range transport of anthropogenic pollution and biogenic emissions on air quality and air chemistry in the marine troposphere over the remote Atlantic and the Eastern Pacific. We are also interested in whether ship emission regulations are being followed. Therefore, trace gas profiles were retrieved in the marine troposphere, and the measurements will be compared with satellite and model data, which enables us to assess the air pollution of ships on a larger scale.

Unfortunately, we did not have permission to measure in the Panama Canal or near the coast, where we expected to find more ship and anthropogenic emissions than, for example, in the middle of the Atlantic Ocean.


RV Sonne (Photo: Miriam Latsch)

Besides the scientific work that had to be done, we experienced a very special and interesting life on board during the cruise. The most exciting days were celebrating Christmas and New Year’s Eve on the ship with people from eleven nations at warm tropical temperatures. We learned some rituals from other countries, sang the most popular national Christmas songs in different languages, danced a Scottish ceilidh dance, and exchanged presents at Secret Santa. Furthermore, it was the first time in our lives, that we toasted the New Year five times on the same day due to the many nationalities. After a long time on board, seeing mainly only water around us, we ended the working part of the cruise in the Pacific with a tour around the RV Sonne in the ship’s boat, seeing the big RV Sonne from an unfamiliar perspective as a small ship in the big ocean (see photo above).

GMAP-2021 campaign in South Korea

Kezia Lange, 01.04.2022

In October and November 2021, four members of the DOAS group participated in the GEMS Map of Air Pollution (GMAP-2021) campaign in South Korea. This campaign brought together instruments from South Korea, the US, Belgium, the Netherlands, and Germany to collect data on air pollution in South Korea for the validation of the GEMS (Geostationary Environment Monitoring Spectrometer) satellite instrument. We installed a MAX-DOAS instrument on the rooftop of the NIER (National Institute of Environmental Research) building at Incheon, close to Seoul. Similar instruments were deployed by other groups in the Seoul Metropolitan Area and other parts of South Korea. In addition, we performed car DOAS measurements coordinated with two other car DOAS instruments operated by the Max-Planck Institute for Chemistry and the Belgian Institute for Space Aeronomy, airborne DOAS and the GEMS measurements. All these instruments provide data on the abundance of NO2, HCHO and SO2, which is valuable for validating GEMS retrievals.


Group picture of some participants on the NIER rooftop. The IUP MAX-DOAS telescope is operating in the left background. (Photo: Steffen Dörner)


Car DOAS instrument measuring pollution distribution in Gangnam, Seoul, crossing the Han River. (Photo: Kezia Lange)

Besides the scientific work, we had several opportunities to have delicious Korean food for dinner with our European and Korean colleagues. We had traditional Korean barbecue, Tteokbokki, Buchimgae and a lot of Kimchi together with Korean beer and Soju.

On days without measurements, we had the chance to explore Seoul, the area of our measurements, from a different perspective. We visited the traditional palaces Gyeongbokgung and Changdeokgung in the middle of the modern, busy city, the historical mountain fortress Namhansanseong and Namsan tower, the second-highest point in Seoul from which one has a great view over the city with its population of 9.7 million people. Thanks to various efforts, air quality has improved over the last years, but air pollution remains a significant problem with high amounts of NO2 we could measure on several days. High aerosol load also continues to be a problem, as can be seen in the photo showing the view from the fortress to the city of Seoul.


Two Korean women in the traditional hanbok in front of the Gyeongbokgung palace entrance gate. (Photo: Andreas Richter)


View from the Namhansanseong fortress to the city of Seoul with the 555.7 m high Lotte World Tower, the sixth tallest building in the world, on a hazy day. (Photo: Kezia Lange)

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