Using Sentinel-5P and Models to Analyse Air Quality Changes since the Coronavirus Outbreak

Abstract:

Since the outbreak pf the Corona virus, many regions have seen strict lockdown, curfew or other movement restrictions. These restrictions lead to substantial reductions in traffic, particularly across cities where normally low air quality is a contributor to poor health. Satellites are well suited for monitoring of such environmental impacts. The recently launched Sentinel-5P TROPOMI is the most powerful air quality sensor in orbit. With a resolution as high as 7 km × 3.5 km, it has the potential to detect air pollution over individual cities.

We have used TROPOMI nitrogen dioxide (NO2) data to monitor changes over many regions of the world since the Coronavirus outbreak and can observe significant drops in NO2 well correlated with local lockdown measures often followed by a more recent recovery.

The interpretation for the UK is hampered by frequent cloud cover and individual days will subject to large data gaps. We can still observe a reduction in NO2 concentration over the UK from satellites and we can show that satellite observations are consistent with in-situ data acquired within cities. However, whilst he observations are sensitive to changes in emissions, as for in situ observations, one needs to be careful in using data only for interpretation of temporal changes due to the impact of meteorology (including wind dilution), sampling bias to certain days and photochemistry.

To support the interpretation of the satellite (and surface) data, GEOS-Chem 3D chemical transport model simulations have been conducted using a nested high-resolution domain over Europe with a resolution of 0.25 x 0.3125. We simulate a business-as-usual scenario and a lockdown scenario with reduced NOx emissions which can be evaluated against NO2 observations. The model also shows the impact on other primary and secondary air pollutants and we observe increasing surface ozone concentrations, in particular over cities, and decreasing PM2.5 over western UK.