Data published by the European Environment Agency and other research institutes have shown a sharp decline in air pollutant concentrations in many European cities where lockdown measures have been implemented. This specifically holds true for levels of nitrogen oxides (NOx) and the decrease is mainly a result of reduced road transport in cities under lockdown. In some cities, such as Madrid, concentrations went down by more than 50 per cent from one week to the next.

While the correlation of clean air in cities and the lockdown these cities experienced might seem more than obvious, researchers caution that it is a bit more complex than what it looks like. As atmospheric chemistry is influenced by weather conditions, a change in emissions of air pollutants does not account for a linear change in concentrations. This means that while reduced human activity – in particular road traffic as a consequence of the lockdown – has led to a reduction of NOx emissions and in a lot of cities to better air quality, the exact drop in emissions still needs to be studied further. Modellers and other air pollution experts discussed the effect of the lockdown on emission projections for 2020 during a recent online meeting (11-14 May 2020) of the Task Force on Emission Inventories and Projections under the UNECE Convention on Long-range Transboundary Air Pollution (Air Convention).

Less nitrogen oxides in the air we breathe reduce risks to our and nature’s health. However, the quality of our air is determined by a variety of pollutants, some of which have not seen a similar decrease in concentrations during the lockdown. Specifically, this holds true for fine particles (PM2.5). The reason is that concentrations of particle pollution undergo even more complex chemical transformations in the atmosphere than other pollutants and the sources are much more varied. Heating of residential and other buildings and the application of fertilizers in agriculture at this time of the year are the main sources of particle pollution – sources that have not been affected as much by the lockdown.

As discussed in a recent online meeting (12-13 May 2020) of the Task Force on Health under the UNECE Air Convention, this shows that while transport-related levels of NOx pollution have gone down, a reduction in traffic does not have a similar effect on levels of fine particles in cities. According to data published by the European Environment Agency, particulate pollution alone caused over 400,000 deaths across Europe in 2016 with NOx pollution accounting for a further 71,000 fatalities. To effectively reduce exposure to air pollution in cities, it is therefore important to look at comprehensive cross-sectoral abatement strategies that go beyond just the transport sector.

The UNECE Convention on Long-Range Transboundary Air Pollution (Air Convention) is a unique regional instrument to support such a comprehensive approach. Its amended Gothenburg Protocol, in force since October 2019, establishes legally binding emission reduction commitments for almost all major air pollutants and their groups, for all economic sectors and emission sources.