Coronavirus / Satellite images show fall in air pollution over European cities amid lockdowns

Satellite images from the European Space Agency show a massive drop in air pollution levels across European cities due to coronavirus isolation measures.

New data captured by the ESA Copernicus Sentinel-5P satellite shows a strong reduction in nitrogen dioxide concentrations over major European cities.

The change in the amount of NO2 in the atmosphere is particularly stark in Paris, Milan and Madrid, according to the ESA. 

The coronavirus has been spread around the world and to combat this spread and ease demand on health services countries have gone into lockdown.

Copernicus has mapped air pollution levels across Europe since the outbreak of the virus and found a 'significant drop' coinciding with new lockdown measures.

The images show a dramatic difference in NO2 levels across all European cities, particularly in Spain, France and Italy coinciding with the lockdown measures.

It matches similar figures from the London Air Quality Network that showed a sharp drop in air pollution levels over the UK capital city.

This is due to a notable drop in traffic levels on the streets of cities across Europe. 

GPS maker TomTom said the percentage of roads congested with traffic in London dropped from 71 per cent this time in 2019 to just 15 per cent yesterday. 

The UK capital's levels of ultra-fine particulate matter, known as PM2.5, are currently around half that would be normally recorded at this time of year.

This matter is produced in a large part from vehicles and burning fossil fuels.  

Scientists from the Royal Netherlands Meteorological Institute (KNMI) have been using data from Copernicus Sentinel-5P satellite to monitor both weather and pollution over Europe. 

The satellite images show nitrogen dioxide concentrations from 14 to 25 March 2020, compared to the monthly average of concentrations from 2019. 

Henk Eskes, from KNMI, explains why these dates were chosen, 'The nitrogen dioxide concentrations vary from day to day due to changes in the weather. Conclusions cannot be drawn based on just one day of data alone. 

'By combining data for a specific period of time, 10 days in this case, the meteorological variability partly averages out and we begin to see the impact of changes due to human activity,' Eskes said.

'The chemistry in our atmosphere is non-linear. Therefore, the percentage drop in concentrations may differ somewhat from the drop in emissions. 

'Atmospheric chemistry models, which account for daily changes in weather, in combination with inverse modelling techniques are needed to quantify the emission based on the satellite observations.'

The latest images and data focus on Italy, Spain and France but they are working on studying data for parts of northern Europe including the UK and Netherlands. 

'New measurements from this week will help to assess the changes in nitrogen dioxide over northwest Europe,' ESA said.  

The multi-national space agency did confirm that levels of the pollutants over London are significantly lower than in March 2019.   

European Environment Agency (EEA) data shows that air pollutant concentrations in Rome and Milan have dropped by 50 per cent, while a Paris air quality monitoring agency recorded up to a 30 per cent decline in pollution. 

The KNMI team, in collaboration with scientists worldwide, have started to work on a more detailed analysis using ground data, weather data and inverse modelling to interpret the concentrations observed.

They are using this data to estimate the influence of the shutdown measures. 

'For quantitative estimates of the changes in the emissions due to transportation and industry, we need to combine the Tropomi data from the Copernicus Sentinel-5P satellite with models of atmospheric chemistry,' said Henk.

'These studies have started, but will take some time to complete.'  

As daily life grinds to a halt in the UK due to restricted movement to control the spread of COVID-19, air quality has improved due to a sharp reduction in traffic. 

These promising early signs suggest air pollution could be falling across UK cities while the pandemic goes on. 

'Air quality has started to improve in many UK cities, mirroring what has been seen in other countries that have restricted travel and levels of outdoor activity,' said Professor Alastair Lewis, from the National Centre for Atmospheric Science, University of York.

'This is primarily a consequence of lower traffic volumes, and some of the most clear reductions have been in nitrogen dioxide, which comes primarily from vehicle exhaust. 

'However fine particles (PM2.5) have also reduced significantly.

'In London for example, PM2.5 is noticeably lower than would be expected for this time of year at the roadside, and these reductions stretch through into the suburbs as well.'  

Professor Lewis said it's especially important to consider how PM2.5 levels have changed compared to what is normally seen at this time of year. 

'Air pollution is noisy, changing with weather and so on,' he said.  

'It's really best to compare where we are now against where we might have expected to be based on previous years.'

London Air Quality Network, a King's College London project, comprises more than 100 continuous monitoring sites in the majority of London's 33 boroughs. 

The data shows that PM2.5 levels in the capital are currently about half those seen on average from 2015 to 2019, as measured in micrograms (one-millionth of a gram) per cubic meter air (µg/m3). 

These fine inhalable particles have diameters that are generally 2.5 micrometers and smaller.

The average human hair is about 70 micrometers in diameter – making PM2.5 about 30 times larger than the largest fine particle. 

It is not yet clear what the health impacts of reductions in air pollution, which causes an estimated 40,000 early deaths in the UK each year, will be. 

Air pollution is linked to health problems including stroke, heart disease, lung cancer and disease, and respiratory diseases and infections, as well as stunting the growth of children's lungs.