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Analysis of Aerosol Transport Patterns from Northern Europe into the Arctic - a Campaign-based Match Study using Raman Lidar Data from Multiple Stations

Final Report Summary - ANNA (Analysis of Aerosol Transport Patterns from Northern Europe into the Arctic - a Campaign-based Match Study using Raman Lidar Data from Multiple Stations)

The general aim of this study is to investigate the Arctic haze hypothesis by exploring the aerosol transport pathways from Northern Europe into the Arctic. This will be done by combining state-of-the-art ground-based measurements, i.e. lidar and photometer remote sensing measurements and trajectory analysis. The project focuses on defining the pathways and origin and thus, improving the aerosol model descriptions and climate predictions in the Arctic. We will evaluate and conduct measurements of vertical aerosol profiles and their properties in Finland, Norway and on Svalbard. Such information is not yet available from Finland and hence this project will fill the gap of the lidar measurements in continental Europe and at Arctic sites. The results will be compared with ECHAM climate model coupled with SALSA aerosol module to evaluate the model properties affecting the aerosol transport to the Arctic.

The detailed aims are to
1. Characterize aerosol transport pathways into the Arctic during the spring months by conducting two spring measurement campaigns (February - May 2013 and 2014). Simultaneous data will be obtained at five Raman lidar measurement sites in Finland, Norway and on Svalbard,
2. Establish a Raman lidar data base of the results obtained from the northern European, sub-Arctic and Arctic measurement sites,
3. Identify aerosol occurrences and characteristics,
4. Identify match cases, in which the same air mass has been probed at least twice on its northward transport and follow the transformation and possible ageing effects of these particles on their pathway,
5. Test the aerosol climate model ECHAM5-HAM-SALSA against measurement data in horizontal and vertical dimensions.

Aerosol transport pathways into the Arctic during the months January to May were characterized. Two spring campaigns were conducted. Data is available from four stations: Kuopio, Sodankylä, Hornsund and Ny-Ålesund. A data base of the data availability was set up. From the beginning of January until the end of May, the Kuopio based PollyXT delivered data on 95% of the days. The KARL in Ny-Ålesund, The MARL in Sodankylä and the Hornsund lidar delivered data on 43, 31 and 25% of the available days. Other available data are three CIMELs in Kuopio, Sodankylä and Hornsund with about 50% data availability as well as Halo Lidars in Kuopio and Sodankylä with 85 to 100% data availability and an MPL and a SP1A in Ny-Ålesund with 99 and 63% data availability. Several aerosol layers, mainly in March and April 2013, have been detected with PollyXT. Unfortunately, these air masses mostly had Arctic origin. The identification of aerosol occurrences and characteristics is ongoing and some case studies have been performed. The match case identification has been started. A match case warning strategy has been set up and is in test phase. In the current version, 4 daily runs at 4 different altitudes from 5 different stations result in station dependent warnings. Out of 384 runs (4 times daily), with 4 altitude trajectories from 5 different stations, e.g. 7680 trajectories are analyzed. 861 of these trajectories result in red warnings. The northward transport has been rather limited within the winter 2013, 78% of the red warning trajectories were associated with southward transport. Only 5% of the red trajectories from the mainland reached Svalbard. The aerosol climate model has not been tested against measurement data, yet.

As a member of the Association of Polar Early Career Scientists (APECS), the researcher took part in several meetings and presented the project and the PollyXT lidar, e.g. in Sodankylä, where she helped getting the MARL ready for the first field study in November 2012. She also spent one week in Stockholm in spring 2013 in order to possibly extend our lidar data group. She was involved in EARLINET meetings as well. In September 2012, she took part in a meeting in South Italy, in which the European lidar community compared and planned measurement strategies and universal development strategies.

In the first months of this project, the PollyXT lidar had to be set up in Vehmasmäki, 20 km south of Kuopio, since the lidar has been operated in South Africa before that. The setup of this system as well as the relocation of the system to a winter-proof container took about the first 3 months of this project. The data has been collected since then. In spring 2013, the researcher took part in a preparing meeting in Hyytiälä, Finland, in which a long term Atmospheric Radiation Measurement campaign was organized. The campaign is effective from February to September 2014 and will include our PollyXT lidar from April to September 2014.

Quite a large, not scheduled, part of this work was the analysis of polar stratospheric clouds in the lidar data. This analysis has not been done with a PollyXT lidar before, since PollyXT is originally a tropospheric system. With the PollyXT being so far north, it was a surprise that Polar Stratospheric Clouds (PSCs) could be detected with it in December 2012. These data as well as PSC data detected by the MARL and CALIOP data from the CALIPSO satellite have been used to write a paper draft about PSC occurrence in Finland in the 2012/2013 winter.

The main achievements of the terminated project are the deeper collaboration between the Arctic lidar sites, preparing the alert system to study the aerosol transport and collection of the dataset for aerosol occurrence and characteristics. The additional findings on the polar stratospheric clouds are also of interest. Part of the work started in this project will be continued by the research group. The obtained results are beneficial for the scientific community and further studies using the results will benefit the whole society concerned about climatic impact in the Arctic.