Ostrava view
The CLAIRO project of the City of Ostrava has been promoting the use of greenery for local air quality improvements. It was a pioneering initiative in many ways. Due to the complexity and technical nature of the project, it contributed to the development of a number of innovative practices that can be replicated relatively easily by cities across Europe. These are linked to either greenery design, or monitoring of changes in air quality, or greenery care.

Jiri Hudec, the Head of Strategic Development Department at the City of Ostrava, when talking about the uniqueness of the project has highlighted its interdisciplinary nature:

CLAIRO project combined and used the knowledge from several science disciplines. In the project itself, there was a collaboration among three universities, two non-profit organizations, a regional authority and a municipality, which is not quite usual. Beyond the above, there was indeed a great combination of innovative approaches leading to functional ecological planting of greenery and innovative care of greenery in a problematic very polluted location.

As part of CLAIRO almost 500 trees and more than 1700 shrubs were planted in the two target sites of the project. What was key, due to the relatively large number of plants and the high species diversity, the two plots could function as living laboratories for testing the effectiveness of the greenery in air quality improvements. The sites were carefully selected to be able to function as specific case studies. 

Vit Kaspar from the Silesian University in Opava has underlined that:

Other cities can learn (from the project) that for effectively planting trees in a polluted urban environment, it is good to consider the perspective of multiple actors and stakeholders from different professional backgrounds.

In the CLAIRO project, during the selection of plant species, air quality experts, foresters and botanist were involved and the interests of the city and local stakeholders were also taken into account. Air quality experts could provide essential information on the spatial distribution and temporal dynamics of pollutant concentrations, while foresters and botanist could provide support on which tree species are suitable for local habitat conditions. At the same time, for the representatives of the local municipality, it was relevant to know which species are available, which ones are less costly on the market, or whether the use of species is in line with local legislation, for instance, if they are indigenous and not invasive. When cities intend to rely on green infrastructure for mitigating air pollution in urban areas, all these aspects should be addressed by the involvement of the representatives of relevant fields of expertise.

The question arises as to which of the practices introduced by CLAIRO can be adopted by other cities and how? Which elements of the project are the best suited to be replicated elsewhere and how?


Ostrava lends a hand to cities on greenery design and modelling capture

First of all, what is the most obvious, urban authorities can easily build on the CLAIRO experience when they intend to use green infrastructure for the removal of air pollutants. First-hand support is offered to them by the CLAIRO partnership. Detailed guidance is provided by the project to cities on how to design greenery for air quality improvements and on how to model pollution capture by planted vegetation in the form of a more detailed methodology paper and a shorter manual.

What’s more, a very practical tool, a comprehensive online database of plants was developed for urban practitioners that help them in designing greenery for the filtration of air pollutants. The database combines state-of-the-art findings from several relevant published sources. It includes over 150 tree species that are more resistant to air pollution and have higher pollutant capture efficiency.

When planted, removal rates of each individual woody plants were modelled. Referring to the modelling work undertaken in CLAIRO, Vit Kaspar has noted:

Other cities may easily apply and replicate the physical models of air pollution deposition and removal when, for example, they intend to compare the purifying effects of existing and potentially planted vegetation.

The methodology paper provides help for the related calculations.


Low-cost sensors open up new dimensions in air quality monitoring

Given the relatively small project target areas, the impacts of the planted trees and shrubs on pollution capture could be verified with the help of hyperlocal air quality monitoring. The solution for gathering data in Ostrava from many monitoring points was the installation of a network of low-cost air quality sensors that ensured high data resolution in space and time, and enabled continuous measurements with fast responses to concentration changes at little expense. Talking about the development of the sensor network, Pavel Bucek from the Technical University of Ostrava indicated:

We have gained fair amount of experience about sensor networks and their use. To our knowledge, at the beginning and during the CLAIRO project, no other project was using as many sensors in the network as we did.

The project has successfully demonstrated the effectiveness of air quality sensors for the quantification of pollution removal, indicating that sensor networks are quite robust and stable, especially for particulate matter.

But CLAIRO has also provided important lessons for those cities that would use the sensors for other purposes. There is a general lack of information on measurement validity of sensors when they are used for more than one year. CLAIRO offered a unique opportunity in this regard, providing a huge set of measurement values from sensors operating longer than 18 months. The good news was that sensors had a service life longer than expected. Besides it was proven that low-cost sensors can provide urban authorities with high-density data that can effectively complement the measurements of official monitoring stations, helping the monitoring of trends and enabling the prediction of changes in air quality at hyperlocal scale. 


An ecological treatment method replacing the use of inorganic fertilizers

A special innovative treatment was applied by Palacky University Olomouc on the newly planted greenery to improve its resistance to various abiotic stress factors. This was necessary in order to increase the plants' long-term ability of the plants to improve air quality at the polluted target sites.

This component of the project was actually the most popular among cities which were informed about the achievements of CLAIRO. Two cities in the Moravian-Silesian Region of Czech Republic and one in Slovakia have already decided to adopt the treatment method piloted in CLAIRO.

There are also a number of applications in the City of Ostrava. Among others, the smart treatment is planned to be applied in eight different green space projects across the city. In addition, the City of Ostrava has recently greened the tram tracks on one of the main roads in the southern part of the city. Tram tracks are currently being greened also in another main road nearby. The company responsible for the projects plans to strengthen the vegetation that is exposed to extreme temperatures during summer with the help of the smart treatment.

Green tram track, Ostrava
Green tram track, Ostrava (Source: City of Ostrava)


The preparation that was designed for the innovative treatment of CLAIRO is the unique result of up to 20 years of research carried out in the Laboratory of Growth Regulators, that is a joint facility of the Palacky University and the Institute of Experimental Botany of the Czech Academy of Sciences. This specific preparation includes biostimulants and a cytokinin derivative, a particular plant hormone acting as the active substance of the mixture.

The innovative treatment itself is fast, simple and inexpensive. As it was explained by Karel Dolezal, the Head of the Department of Chemical Biology at Palacky University Olomouc, the application of the smart treatment piloted in CLAIRO does not take more time than a conventional one based on the use of inorganic fertilizers and watering. Karel Dolezal has highlighted:

It is as simple as conventional treatment, and as frequent. It is much more ecological, the compounds are organic, and added in very low concentrations, that is why it is also cheaper, in comparison with conventional treatment.

The key here is that plant hormones can regulate physiological processes already at extremely low concentrations.

In general, this novel practice can be adopted by other cities just as easily as the conventional treatment. On top, the smart plant treatment can actually be applied on all types of urban greenery, such as urban forests, parks, green roofs or green tram tracks. During the transfer of the practice, municipalities can rely on their park maintainers or the specialists responsible for greenery care. The use of the innovative treatment can be beneficial wherever greenery is stressed by negative environmental factors.

The innovative plant treatment is already commercialized. The preparation used in CLAIRO is subject of several international patents licensed to Czech and foreign companies operating in the field of foliar fertilizers.

The vitality of the treated plants can also be monitored relatively easily. Karel Dolezal has pointed out that the monitoring activity can be performed by any team educated in plant physiology and most of the physiological parameters can be monitored with low-cost equipment directly in the field in a relatively short time.


Flying drones to quantify urban vegetation

Drones had a significant role in modelling pollution removal by plants at the Ostrava target sites. Originally conventional ground-based measurements were performed in CLAIRO for the quantification of vegetation properties. Then the research team of the Silesian University in Opava replaced the standard ground-based data collection with drone-based measurements to test the potential of this novel technical solution. The use of drones was combined with canopy photography (hemispherical photography), using upward looking extreme wide-angle lens. The drone data together with the data sourced from the canopy photography could be scaled up into a continuous detailed map. As opposed to the conventional practice, a finer spatial resolution was achieved leading to a higher level of accuracy for predictions of pollution removal. Vit Kaspar has pointed out:

Drones were able to provide detailed information about vegetation characteristics, which made it possible to estimate the capture of pollutants not only for entire forest stands, but also for specific species and individual woody plants.


View of Radvanice target site from drone
View of Radvanice target site from drone (Source: Silesian University in Opava)


When the aim is the quantification of urban vegetation, the use of drones has a range of benefits, opening up new possibilities for urban authorities. With the help of drone-based measurements differentiated information can be gathered by vegetation type, or by life stages of the plants, even on species level. For instance, broadleaf and coniferous trees can be easily distinguished from each other. What is key, it is much less time-consuming and labour-intensive to use drones for the quantification of the vegetation input parameters than to conduct ground-based measurements for this reason. Moreover, flight missions can even be repeated easily at a relatively low cost.



Bílek, J., Bílek, O., Marsolek, P., Bucek, P. (2021) Ambient Air Quality Measurement with Low-Cost Optical and Electrochemical Sensors: An Evaluation of Continuous Year-Long Operation. Environments. 2021; 8(11):114. https://doi.org/10.3390/environments8110114

Kaspar, V., Zapletal, M., et al. (2022) Unmanned aerial systems for modelling air pollution removal by urban greenery. Urban Forestry & Urban Greening, Volume 78, 127757, ISSN 1618-8667, https://doi.org/10.1016/j.ufug.2022.127757.

About this resource

Tamás Kállay
Ostrava, Česko
About UIA
Urban Innovative Actions

The Urban Innovative Actions (UIA) is a European Union initiative that provided funding to urban areas across Europe to test new and unproven solutions to urban challenges. The initiative had a total ERDF budget of €372 million for 2014-2020.

Go to profile
More content from UIA
1129 resources
See all

Similar content