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The observational part of our research is largely based on measurements carried out at the Kumpula station in Helsinki. We have two active sites where the fluxes of CO2, H2O, heat and aerosol particles are continuously measured using the eddy covariance (EC) technique (Fig. 1). The two sites represent different land uses: the semi-urban Kumpula (blue) has been running since 2004 (Vesala et al. 2008, Järvi et al. 2009) and the urban site, Hotel Torni (red), since 2009 in the city centre representing a highly built-up land cover (Nordbo et al. 2013, Kurppa et al. 2015). Within the approximate footprint of the Kumpula site, half of the surface is covered with vegetation, whereas in city centre the fraction is only 22%. Kumpula is also ICOS (Integrated Carbon Observation System) associated ecosystem station. In addition to the long-term measurements, we have conducted several EC measurement campaigns related to other compounds including COS, VOC, CO and N2O.
Using the observations, we try to understand how different urban land uses affect the surface exchange processes with particular emphasis on the role of vegetation. We have also extensive ecophysiological observations made in Helsinki area to understand in detail the gas exchange and functioning of urban vegetation. The observations are also used in urban land surface model development.
The current and past projects are
Figure: The locations of the two eddy covariance (EC) stations in Helsinki (Karsisto et al. 2015). The 1 km circular areas around the station approximate the source areas for the EC measurements.
We actively participate to the development of the Surface Urban Energy and Water Balance Scheme SUEWS (Järvi et al. 2011, 2019, Ward et al. 2016) in collaboration with Prof. Sue Grimmond from the University of Reading. The model simulates the energy and water balance components, and CO2 surface exchange through the use of commonly measured meteorological variables and information on the surface cover. The model is part of the Urban Multi-Scale Environmental Prediction Tool (UMEP, Lindberg et al. 2017). Besides model development, we use SUEWS to examine both long- and short-term behavior of the surface exchanges in different urban areas (Helsinki, Zurich, Paris, Munich, Beijing, Minneapolis, Swindon,...). Current study interests is particularly the potential of urban green areas to sequester carbon from the atmosphere at the same time when regulating heat. The current and past research projects are
Figure: Modelled energy balance at the urban site (Rl) in Montreal during (a) cold snow, (b) warm snow and (c) snow-free periods in 2007-2008 using SUEWS (Järvi et al. 2014).
We develop and use the PALM model system to examine flow fields and air quality in various cities (Helsinki, Paris, Beijing, Malmö). We have added the sectional aerosol particle model (SALSA) in PALM so that it can be used to simulate aerosol particle size distribution within complex urban landscapes. Current research topics include the impact of urban planning and increasing amount of electric vehicles on local air quality , structure of coastal urban boundary layer, and impact of thermal turbulence on local air quality. Current and past research projects are
Figure: Flow field in central Helsinki as simulated using PALM model using detailed surface model (M. Auvinen).
| Project | Funding period | Persons | Funder |
| Artificial Intelligence for Urban Low-Emission Autonomous Traffic (AIforLessAuto) | 2022-2024 | Leena Järvi, Pak Lun Fung, Omar Al-Jaghbeer, Nahid Atashi | Research Council of Finland |
| Research Infrastructures Services Reinforcing Air Quality Monitoring Capacities in European Urban & Industrial AreaS (RI-Urbans) | 2021-2025 | Leena Järvi, Jani Strömberg | EU framework H2020 |
| Pilot Application in Urban Landscapes - towards integrated city observatories for greenhouse gases (PAUL/ICOSCities) | 2021-2025 | Leena Järvi, Minttu Havu, Jani Strömberg, Jesse Soininen, Anni Karvonen | EU framework H2020 |
| Individuals, communities and municipalities mitigating climate change by carbon smart green space (CO-CARBON) | 2020-2026 | Leena Järvi, Michael Lee, Johanna Hohenthal, Minttu Havu | Strategic Research Council |
| Integrated Carbon Observations System (ICOS) | 2008-present | Leena Järvi, Jesse Soininen | Faculty of Science |
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Optimal urban planning solutions for maximizing the beneficial impact of urban green space on surface-atmosphere exchanges of energy, water and CO2 |
2022-2025 | Michael Lee | Doctoral School in Atmospheric Sciences |
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Modelling and observing the atmospheric boundary layer in coastal cities |
2021-2024 | Sasu Karttunen | Doctoral School in Atmospheric Sciences |
| Sustainable urban development emerging from the merger of cutting edge Climate, Social and Computer Sciences (CousCOUS) | 2020-2024 | Leena Järvi, Xiaoyu Li, Nahid Atashi | Research Council of Finland |
| Urban green space solutions in carbon neutral cities (CarboCity) | 2019-2023 | Leena Järvi, Jesse Soininen, Yiyang Ding | Research Council of Finland |
| The most optimal green area solutions in present day urban planning to maximise urban carbon stocks | 2019-2023 | Minttu Havu | Tiina and Antti Herlin foundation |
| Associate professor starting package | 2019-2022 | Jani Strömberg | University of Helsinki |
| Smart urban solutions for air quality, disasters and city growth | 2017-2021 | Leena Järvi, Mona Kurppa | ERA-PLANET |
| Modelling air quality and ventilation inside city blocks using large-eddy simulations | 2017-2020 | Mona Kurppa | Doctoral School in Atmospheric Sciences |
| Fine resolution air quality modelling as support of urban planning | 2017-2018 | Leena Järvi, Mona Kurppa, Sasu Karttunen | Helsinki Metropolitan Region Urban Research Program |
| Towards reliable prediction of urban climate using novel methodology development | 2017-2018 | Mikko Auvinen | Maj and Tor Nessling foundation |
| Aerosols, Clouds and Trace Gases Research Infrastructure (ACTRIS-2) | 2015-2019 | Leena Järvi | EU H2020 |
| Modelling of the Surface energy and water balance in high-latitude cities | 2014-2016 | Tom Kokkonen | Maj and Tor Nessling foundation |
| Carbon dioxide, heat and water exchanges in urban climate | 2011-2013 | Leena Järvi | Academy of Finland |
| Micrometeorology and air quality in urban areas | 2007-2010 | Leena Järvi | Maj and Tor Nessling Foundation |
Our group collaborates with several research groups both nationally and internationally. The main collaborators for the current research topics are