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Smog under scrutiny by AGH UST scientists

The photo shows Krakow's main square in low air transparency conditions. In the foreground, there is a statue of a man. In the background, there are outlines of historic tenements. There are passers-by on the square.

Krakow's Main Square, photo by AGH UST

Smog under scrutiny by AGH UST scientists
air pollution covid

Which meteorological factors determine the inflow and lingering of smog in Krakow? What is the role of topography? Does the pollution produced during the heating season come mainly from Krakow or the neighbouring towns? These are some key questions asked by scientists from AGH University of Science and Technology in Krakow. The answers to them have been found in research projects carried out during the COVID-19 pandemic. The results were published in one of the most frequently cited journals in the world, "Scientific Reports".

In the investigations carried out during the pandemic, scientists from the Faculty of Geology, Geophysics, and Environmental Protection have collected data from several dozen sensors scattered across Krakow and neighbouring towns. The most significant conclusions of the research pertain to the unambiguous connection between Krakow’s topographic location and the air pollution that, to a large extent, flows from neighbouring communes.

‘In our studies, we’ve applied a comprehensive geostatistical approach to spatio-temporal analysis of particulate matter (PM) concentrations. The data have been collected by a dense network of Airly sensors and reference measuring stations of the Chief Inspectorate Of Environmental Protection. The results point to a relationship between topography, meteorological variables, and PM concentrations. The two main factors include the speed of the windand the lie of the land. Studying the PM2.5/PM10 ratio allowed us to extensively analyse spatial pollution migration, including the variety of its sources. These investigations have demonstrated that the unfavourable location of Krakow makes the city susceptible to the accumulation of pollutants from neighbouring communes. The chief source of air pollution within the studied period was out-of-city heating using solid fuels’, ephasises Dr Mateusz Zaręba from the research team investigating pollution. The pandemic has provided the scientists with unique conditions to observe the influence of solid fuel heating on PM concentrations due to the reduced levels of transport pollution.

Krakow’s topographic map with locations of the Airly sensors, district boundaries, and main rivers of the city; image by the AGH UST

The image shows the outline of the Krakow agglomeration with air pollution sensors locations marked thereon.

The researchers point out that the main sources of pollution have changed over the years. At the beginning of the 1970s, the chief source of pollution was the metallurgical industry. However, as the number of city residents increased, the proportion of solid fuel heating as a pollution source also did so, finally becoming the dominant source in winter. In Krakow, city officials have introduced a complete ban on using solid fuels for heating; therefore, the main sources of pollution remain outside of the city.

Hence, in late autumn, winter, and early spring, the chief source of pollution in Krakow is the solid fuel heating. The second factor is motor transport, the intensity of which also varies throughout the year.

The current pollution problem in Krakow is related to the geographical location of the city, say the scientists. ‘In particular, the location of Krakow, surrounded by hills in the north and south, determines the proglacial stream valley of the Vistula River as the main route of pollution inflow. Despite numerous laws banning the use of solid fuels for heating, pollution still migrates to the city from outside, which, on a number of winter days, makes it one of the most polluted cities in the world’, Professor Tomasz Danek claims.

The images show the boundaries of Krakow. With colours from blue, through green and yellow, to red, temperature ranges have been marked.

Temperature, PM1, PM2.5, and PM10 maps of Krakow on March 18, 2020; image by the AGH UST

The purpose of the article was to investigate the influence of meteorological factors and topography on air pollution in Krakow and the migration of that pollution using geostatistical methods. The results show that pollution in Krakow in the period studied has been predominantly caused by the migration of pollution from neighbouring communes, where local governments still allow residents to use solid fuels for heating. ‘In our research, we’ve analysed the concentrations of PM2.5 and PM10 in Krakow and conterminous towns. Moreover, we’ve demonstrated the main directions of air pollution migration in relation to the direction of the wind. We’ve applied a statistical analysis to check the relationship between PM2.5 and PM10 concentrations, and other physical properties of the atmosphere. Measurements included atmospheric pressure, temperature, and humidity. We’ve collected the data in early spring 2021, when the intensity of motor transport was reduced due to a partial lockdown caused by the COVID-19 pandemic in Poland. This allowed us to observe air pollution caused by solid fuel heating in conditions where the interference of road traffic-generated pollution has been significantly limited’, Professor Danek explains.

Standardised GWR model of PM10 and PM2.5 (plus their ratios) flowing into Krakow (based on the analysis of meteorological and topographic factors); image by the AGH UST

The images show the boundaries of Krakow. With colours from blue, through green and yellow, to red, temperature ranges have been marked.

The principal conclusions of the investigation include the following:

  • The dominant factors within the period studied, which were conducive to the migration of pollution into the city, included wind speed and azimuth. Atmopsheric pressure played the key role in stopping the pollution;
  • The dominant factor influencing pollution generation outside of the city was the temperature, more specifically, the subjective sensation of chill;
  • The complex morphology of the terrain and the location of Krakow in a valley were the key factors influencing the migration and lingering of the pollution. The Krakow-specific tendency for fog formation additionally slowed down the outflow of pollution;
  • We need coordinated actions between Krakow and the neighbouring communes to improve the quality of air within the entire agglomeration. The actions taken by the city of Krakow in separation, although relevant, will never suffice.


‘Other conclusions that emerge from the investigation definitely include the fact that studying multiannual trends in PM10 concentrations in Krakow prove that information and educational campaigns are vital factors that initiate changes that lead to the improvement of air quality’, Elżbieta Węglińska states.

The research team, led by Professor Tomasz Danek from the AGH UST Faculty of Geology, Geophysics, and Environmental Protection, includes: Dr Mateusz Zaręba and Elżbieta Węglińska, doctoral student from the Department of Geoinformatics and Applied Computer Science. Full text of the article on the Nature website.

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