Atmospheric Research in a Passenger Aircraft

Atmospheric Research in a Passenger Aircraft

Author: Xin Su, Yafang Cheng

Dr. Yafang Cheng from the Max Planck Institute for Chemistry in Mainz, Germany, uses a passenger aircraft for comprehensive scientific research. Here she talks to Dr. Xin Su for ChemViews Magazine about the CARIBIC project, recent research results, and her motivation. The project name is an acronym for civil aircraft for the regular investigation of the atmosphere based on an instrument container.



Can you give us some brief background information on the CARIBIC project?

The CARIBIC project uses a passenger aircraft for comprehensive scientific research, with a focus on improving our understanding of climate, atmospheric chemistry, and physics.

It was initiated by the Max Planck Institute for Chemistry, the Karlsruhe Institute for Technology (KIT), and the Leibniz Institute for Tropospheric Research, all Germany. It started in 1997 on a Boeing 767 of LTU International Airways, and then was implemented on an Airbus A340-600 of the Lufthansa German Airlines in 2004. In 2012, the CARIBIC project was integrated into the IAGOS (in-service aircraft for a global observing system) European Research Infrastructure.

Currently, the IAGOS-CARIBIC project has about twelve scientific partners from the EU and US. This means that they are scientific partners joining the project with different instruments installed in a large airfreight container. It is loaded onboard the cargo bay of the Lufthansa Airbus. We joined the project with measurements of single black carbon particles in August 2014.



And these measurements are only possible through the partnership?

Yes. The CARIBIC project is worldwide unique. It makes it possible to carry out such comprehensive scientific measurements at high altitude on a regular basis with relatively low cost. Thus, it provides extensive data from the upper troposphere and lowermost stratosphere. This is essential to understand the human impact on climate change and the changing atmosphere.

Another advantage is that the high payload allows us to equip the flying observatory with a comprehensive collection of scientific instruments, currently about 1.5 tons. This comprehensive setup enables simultaneous scans of multiple trace gases and aerosol particles. We hope to gain new insights into their formation and transformation mechanisms.



How are the measurements performed?

All online instruments and off-line sampling devices are installed in a modified container stored in the aircraft. The measurements are unmanned and fully automatic. The power supply comes from the airplane. The sampling of the outside air is done through a special air and particle (aerosol) inlet underneath the aircraft.



What kind of scientific instruments are loaded into the cargo compartment?

The so-called “passenger aircraft container laboratory” container includes 19 instruments for in situ measurements of ozone, carbon monoxide, carbon dioxide, nitrogen oxides, methane, water vapor, cloud water/ice, water isotopes, acetone, acetonitrile, mercury, black carbon, bioaerosols, dust particles, and much more. The CARIBIC container also includes a system for collecting more than 116 air samples. For each sample, more than 40 gases are measured at different laboratories in Europe.



Is the data transmitted automatically to your lab or do you collect air samples and then analyze them in the laboratory after every flight series?

Our in-situ measurements are performed online during the flight and the data are recorded simultaneously. They are transmitted to our data server after a four-flight series each month.



You said that your group is measuring single black carbon particles?

Yes. We measure the concentration, size distribution, and mixing state of black carbon (BC) aerosols with a single particle soot photometer (SP2). Black carbon is one of the most important climate warming agents. Its climate forcing has been estimated to be about one third that of CO2. Besides its role in climate forcing, black carbon is also a major component of fine particulate matter (PM2.5).

High-altitude black carbon (BC) has a high radiative forcing efficiency and can change the local thermal atmospheric structure (stability) and influence cloud covers. After reaching the lowermost stratosphere (LMS), BC has a long lifetime, which further amplifies these effects. However, because of limited measurements in the LMS—due to technical challenges and the high cost of aircraft measurements—it is still not clear how frequently emissions from burning biomass are transported and to what extent they influence the background BC levels, both in concentration and mixing state.

We have successfully recorded more than 800 hours of data, which to our knowledge is the largest ever collection of observations of high-altitude black carbon, making it a key dataset for evaluating the climate effect of black carbon.



You recently reported a 14-month study of the abundance and evolution of wildfire-emitted black carbon in the lowermost part of the stratosphere. Wildfires inject large amounts of black carbon particles into the atmosphere. Can you summarize this study?

We have found that wildfires can dramatically increase BC mass concentration in the LMS. The black-carbon concentrations in fire plumes were over 20 times higher than in the background atmosphere. In addition, most black-carbon particles were covered with a thick coating of other chemical substances. This enhances their light absorption. Both effects suggest strong local heating in the lowermost stratosphere that may substantially influence the regional climate. However, this remains a challenge for model simulations.



How do you establish and separate the contribution of wildfires?

In this work, we used chemical tracers and air mass trajectory analysis to identify the biomass burning plumes. Carbon monoxide is produced by incomplete combustion. Compared to the background air, combustion emits more carbon monoxide. So, we first used carbon monoxide to screen our data and identified a series of air masses influenced by combustion processes. Acetonitrile (CH3CN) is produced and emitted into the atmosphere almost exclusively during biomass burning events such as wildfires. So, secondly,  we used CH3CN data to distinguish burning biomass from other combustion products.

We used these two gas-phase compounds measured simultaneously with the black carbon as chemical tracers to identify the influence of biomass burning (BB) events to the air mass that we encountered. By using the concentration levels of CO and CH3CN, we classified the air masses into three types: (1) background air, (2) BB-affected air, and (3) BB plumes.



And what did you find?

One of the most intensive BB events occurred from August 17 to 20, 2014. The CARIBIC laboratory allowed a very valuable observation of the atmospheric aging of the BB plume. Two sequential flights from Munich, Germany, to San Francisco, USA, and back divided the same section of the large plume separated by approximately 18 hours of aging. The Aqua and Terra satellites showed that the origin of the revisited smoke plumes was from intensive fires in the Northwest Territories of Canada. The National Oceanic and Atmospheric Administration (NOAA) provided the tools to calculate the forward trajectory of air mass from the source fires and backward trajectory of air mass from the observation point to examine its origin and evolution in the atmosphere. These analyses also confirmed the origin of the observed smoke plume.



What is the next step in your mind following this work?

There is plenty of information you can dig out from this dataset. On the one hand, these high-altitude data can be used to constrain the global models for better estimation of the climate forcing of black carbon. On the other hand, we can use them to investigate the fate of aerosols in the stratosphere and their interactions with clouds. This is essential for understanding the potential consequence of upper-atmosphere-based climate engineering measures.



What got you interested in the CARIBIC project?

One of the most challenging parts in assessing the global estimate of the radiative forcing of black carbon is the lack of direct measurement data, especially at high altitude where the BC particles have much larger forcing efficiencies. Aircraft measurements of BC are very delicate and expensive. Therefore, such measurements have not been performed very often.

I became aware of the CARIBIC project during an Earth Solar Systems Research Partnership (ESRP) workshop in early 2014. I was excited by the opportunity to do regular, long-term measurements of black-carbon concentration and physical-chemical properties, such as the mixing state. So, I talked to Dr. Carl Brenninkmeijer, who oversaw the CARIBIC project at that time, about integrating our single-soot-particle spectrometer into the CARIBIC container. Carl was very interested and we agreed immediately that we should do it. After four months, we modified the commercial instruments of SP2 to fit the CARIBIC container and measurement conditions, fully automatizing the instrument and having it certified with the civil passenger aircraft safety criteria, with help from Droplet Measurements Technology (the company that built the SP2 instrument) and the CARIBIC team. Since August 2014, we have already recorded more than 800 hours of SP2 data.



What motivates you in your work?

Air pollution and climate change are two of the most challenging environmental issues for human beings in the 21st century. Some governments seem to be very reluctant in solving these problems, because of the impact of emission reduction on economic development. Thus, we are looking for more attractive and efficient solutions to save the earth. BC seems to be a perfect candidate, of which the reduction may have a large co-benefit in mitigating air pollution and global warming.

Furthermore, scientists alone are not enough to tackle such a big challenge. I love this project in which we can feel strong support from the industrial partner Lufthansa as well as commitment from funding agencies such as the Max Planck Society, European Union, BMBF, DFG, and so forth.



How has your career developed?

During my Ph.D. study at Peking University in China, I became fascinated by the special role of black carbon. By combining experimental and modeling tools, I successfully retrieved the mixing state of black carbon aerosols, a key uncertainty in its climate forcing. After my Ph.D., I went to Germany and the USA for postdoctoral research and learned to model the regional air quality and global impact of aerosols. Later I joined Peking University as a 100 talent professor, and finally moved to the Max Planck Institute for Chemistry as a W2 research group leader. My current work greatly benefits from the international network I built in my early career period.



What do you do in your spare time?

As a chemist, I love cooking and I am pretty good at it. I am also very interested in the idea of the Anthropocene, the healthy development of a green planet, and colonization of other planets. So, I enjoy watching movies and documentaries about the universe, stars, planets, rockets, spacecraft, and so forth, together with my son.

Yafang Cheng studied chemistry at the Wuhan University, China, and gained her Ph.D. from Peking University, Beijing, China, in 2007. After post-doctoral work at Leibniz Institute for Tropospheric Research, Leipzig, Germany, from 2007 to 2009, and at the University of Iowa, USA, from 2009 to 2011, she became a 100 Talents Professor at Peking University, from 2011 to 2013. Since 2013, Yafang Cheng is a group leader at the Max Planck Institute for Chemistry, Mainz, Germany, leading the Minerva independent research group.


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