How does weather affect air pollution?

Prevailing weather conditions can weaken or improve air quality. Strong winds can rapidly transport pollutants hundreds of kilometres, whereas during weak wind circumstances, pollutants can accumulate around the source of the release. The rain can either clean or pollute the environment depending on harmful substances in the air.

Picture: Minna Rantamäki

The mixing of traffic emissions can be very poor during weak wind circumstances but also strong winds can provide rapid transport to distant locations. For example, long range transported particles can contain pollution from industry and power production as well as pollution from forest fires or swailing (controlled fire in forestry or land-management). Street dust in springtime is a recurring problem in Finland because sand and grit are used to reduce the slippery conditions of streets during wintertime and studded tires increase road dust emissions in urban areas. Also, photochemical reactions are very powerful in sunny and warm weather. For example, surface ozone is more readily formed on warm, sunny days than on cold, cloudy days. Fog and rain can clean the air effectively. At the same time however, chemicals and compounds that pollute the air can fall with rain to pollute soil and surface waters.

Sometimes weather situations change rapidly and naturally these changes reflect on the measured pollution concentrations. For validating concentration observations and for understanding the origin of the pollutants, it is needed to study simultaneously.

  • the weather during observation

  • routes of polluted air flows

  • circumstances during transportation

  • source of release

Air quality in Finland

There are relatively few serious air quality episodes in Finland, because cities are smaller and more thinly-developed and traffic is not as heavy in Finland than e.g. many other cities in Europe. In Finland, high concentration values are measured only sparsely, for a shorter time and in smaller areas compared to other European countries. Although the quality of air in Finland is generally quite good, the concentrations of pollutants can occasionally rise to harmfully high levels in unfavourable weather circumstances.

Authorities' role in air pollution control

Local authorities in municipalities or cities monitor air quality and provide public information pursuant to the Environmental Protection Act. Local authorities in municipalities have a responsibility to arrange air quality monitoring needed in local circumstances and maintain air quality measurement stations in Finland. Measuring air quality however, is a distributed activity in Finland. Local environmental authorities measure air quality in ca. 50 places across the country and the Finnish Meteorological Institute (FMI) measures air quality in ca. 20 background stations which are far from the source of releases in cities. Also operators of different activities have a responsibility to be aware of the impacts of their activities on air quality.

Air quality observations around Finland

All authorities and organisations who measure air quality in Finland can send their observations to be published in real time on the air quality site, which is built and maintained by FMI. Air quality observations have been described with an easy-to-understand colour scale and an air quality index is used to describe the prevailing air quality situation. In addition to the air quality observations also rain and wind observations can be chosen on the same map (rain or wind can weaken or improve air quality). Through the air quality site it is easy to see the current or past air quality situation in Finland with one hour intervals. Prevailing air quality in Finland:

FMI's activities

FMI supports preparedness of municipalities with scheduled plans by offering localized forecasts of conditions favourable for AQ episodes to its customers. The air quality forecasts are based on the meteorological situation and describe the potential risk of weather conditions causing poor air quality or when poor air quality will improve. In addition to forecasts, there are many different air quality research fields in FMI, e.g. air quality assessments in urban and industrial areas and air quality laboratory services.