Earth observation network PollyNet gets new station in Asia
PollyNet stations in Finland, Germany, Greece, Poland, Portugal and South Korea are already continuously measuring dust in the atmosphere by laser. Further stations are planned in Cyprus, Israel, and on the Cape Verde Islands.
For the technology of the stations in Tajikistan, Cyprus and on the Cape Verde Islands, the Federal Ministry of Education and Research (BMBF) has provided almost three million euros to close observation gaps and intensify successful cooperation with these countries.
Thanks to technical support from Germany and on-site support from the Academy of Sciences of the Republic of Tajikistan, the test measurements carried out as part of the CADEX project (Central Asian Dust Experiment) can now be converted into operational long-term measurements that will provide important long-term data for climate and air quality in Central Asia.
In total, dust particles with a mass of around 1910 megatons enter the atmosphere every year. The Sahara is thought to be the main source with about 1150 megatons. So far it can only be speculated how much the deserts and steppes of Central Asia contribute to the total amount of mineral dust in the atmosphere, because for a long time there was a lack of measurements in this important region of the dust belt.
How long and how high dust hovers in the air varies depending on regional weather conditions and particle size. Large particles have a shorter residence time than small and therefore lighter particles, which can quickly reach great heights in updrafts. On average, dust particles remain in the atmosphere for one to two weeks and spread with the wind.
Mineral dust plays a major role in the global climate because the dust particles floating in the atmosphere reflect sunlight and dim the sun's rays arriving on the ground. In addition to this direct effect, there is also a so-called indirect aerosol effect: the particles act as cloud nuclei and influence cloud formation, which also has an effect on the Earth's radiation budget and can cool or warm depending on the type and height of cloud. In addition, there are many other effects whose significance has only slowly been understood in recent years: Chemical reactions can take place on the surface of the dust.
Trace metals in mineral dust fertilize the ocean and drive so many biogeochemical processes in the ocean. Heavy dust outbursts can affect the local infrastructure, such as photovoltaic systems. In addition, there are the effects on people's health, some of whom suffer from severe dust storms: Dust has a negative effect on the respiratory tract and can also transport bacteria and diseases.
It is also important to be able to distinguish the locally produced fine dust from the long-distance transport from other regions of the world. This is the only way to check the effectiveness of measures to protect the climate or the environment. Lidar measurements are also used to investigate the complex interaction processes involved in cloud formation. “Measurement sites in areas with high desert dust pollution play an outstanding role here, as dust particles are good ice nuclei.
In this context, it should be emphasised once again that on a global scale there are few regions in which, as in Cyprus and Tajikistan, the impact of man-made particles, on the one hand, and natural particles from forest fires and desert dust, on the other, can be studied so well. Here we want to make an important contribution to environmental and climate research. Atmospheric research urgently needs such observations for the validation of global aerosol models, which in turn will benefit the improvement of climate models,” stresses Prof. Andreas Macke, Director of TROPOS.
The automated Ramanlidar systems of the Polly type (POrtabLe Lidar sYstem) have been developed by TROPOS for over 15 years, used worldwide and have become central instruments at various measuring stations such as Leipzig or Punta Arenas in Chile. These lidar systems measure particle properties, optical properties of thin clouds and moisture profiles.
“In recent years, the polarization lidar technique has been significantly further developed and now makes it possible to measure the environmental impact of desert and soil dust (fine dust particles) and to determine the climate effect and cloud formation (coarse particles as condensation nuclei and ice nuclei) vertically resolved,” explains Dr. Dietrich Althausen of TROPOS, one of the main initiators of this technique. “In addition, the polarization lidar allows vertically resolved estimates of the concentrations of condensation and ice nuclei in a wide variety of particle mixtures.
The PollyNET concept is methodologically comparable with the global aerosol measuring network AERONET (AErosol RObotic NETwork), whose solar photometer is coordinated by NASA and the University of Lille. “There is a standardized type of measuring instrument, a standardized evaluation software including quality control as well as a leading and responsible research group. PollyNET and AERONET complement each other very well: PollyNet measures the vertical structure and AERONET the vertical sum of the tropospheric aerosol in the air layers, underlines Dr. Ronny Engelmann of TROPOS, who has been in charge of both instruments on various ship expeditions for years. “PollyNET sites are also ideally suited as anchor stations for the ESA space missions Aeolus and EarthCARE”.
As part of the Central Asian Dust Experiment (CADEX), lidar measurements have been carried out since 2015 to study mineral dust over Tajikistan using a smaller, portable lidar version. These measurements with this PollyXT showed the detailed dust distribution in the air column over Central Asia for the first time. Very often dust layers were observed up to high altitudes, partly up to 10 km height. The evaluation of the data as well as regional 3D modelling is still in progress. The CADEX project was financed by the Federal Ministry of Education and Research within the framework of “Partnerships for Sustainable Problem Solutions in Emerging and Developing Countries”. Within this framework, close scientific cooperation was established between the Physical-Technical Institute of the Academy of Sciences of Tajikistan and the Leibniz Institute for Tropospheric Research. In the meantime, the project has been honoured by the BMBF as a “lighthouse project” because it produced outstanding results.
However, the CADEX project was only designed to record a few sample measurements. As a consequence, a measuring container was designed and built at TROPOS in Leipzig with the support of the BMBF, which was transported to Tajikistan by land at the end of May. With the commissioning of the PollyNet station in Dushanbe, the measurements will now be transferred to long-term observations.
“Dust events were often followed by heavy rainfall events. This suggests a connection. But how and to what extent does dust influence these processes? Perhaps the measurements will give us decisive indications in the coming years,” hopes Julian Hofer of TROPOS, who helped to supervise the measurements on site in Tajikistan. The long-term measurements reveal trends that only become apparent over several years. The lidar measurements in Tajikistan will thus provide important data on climate change and air quality in Central Asia. Tilo Arnhold
Dr. Dietrich Althausen,
Senior Scientist , TROPOS Department „Remote Sensing of Atmospheric Processes“
Phone + 49-341-2717-7063 (by telephone attainable starting from 01.07.19, before only via email),
Dr. Ronny Engelmann,
Scientific staff, TROPOS Department „Remote Sensing of Atmospheric Processes“
Phone + 49-341-2717-7315 (by telephone attainable starting from 01.07.19, before only via email),
PhD student, TROPOS Department „Remote Sensing of Atmospheric Processes“
Tel. + 49-341-2717-7336 (by telephone attainable starting from 01.07.19, before only via email),
as well as
Dr. Albert Ansmann,
Leader of the Working Group „Ground Based Remote Sensing“, TROPOS Department „Remote Sensing of Atmospheric Processes“,
Phone + 49-341-2717-7064
TROPOS Public relations
Recent Measurements of PollyNet:
CADEX – Central Asian Dust Experiment:
First dust conference in the Central Asian part of the earth’s dust belt (Press release from 14.04.2019):
Ansmann, A., Mamouri, R.-E., Hofer, J., Baars, H., Althausen, D., and Abdullaev, S. F. (2019): Dust mass, CCN, and INP profiling with polarization lidar: Updated POLIPHON conversion factors from global AERONET analysis, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2019-98 , in review.
Solomos, S., Gialitaki, A., Marinou, E., Proestakis, E., Amiridis, V., Baars, H., Komppula, M., Ansmann, A. (2019): Modeling and remote sensing of an indirect Pyro-Cb formation and biomass transport from Portugal wildfires towards Europe. Atmos. Environ., 206, 303-315 p., https://doi:10.1016/j.atmosenv.2019.03.009
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