Sharp changes in NO2 observed by TROPOMI during lockdowns

Air quality
Since the start of the COVID-19 pandemic, we have tracked closely the evolution of NO2 abundances observed by the TROPOMI sensor. Due to lockdown measures, unprecedented decreases were observed in China, where COVID-19 was first identified. As the pandemic spread around the world, more cities and countries declared lockdown measures. This resulted in a drastic decrease in transportation and industrial activities and led to substantial NO2 reductions ranging between 20% and 50% in many large cities around the world.

Sharp drop and slow recovery of NO2 levels

Figure 1 depicts the evolution of NO2 levels over 5 regions which were strongly affected by the COVID-19 crisis. The figure shows the relative reduction in NO2 in 2020 compared to the observations over the same period in 2019, averaged for all big cities within the region.

As can be seen, average NO2 reductions of up to 50% were observed over Chinese cities at the peak of the crisis, whereas in India, Europe, North and South America, NO2 reductions ranged between 20 and 35% in the first weeks after the initiation of lockdown measures. Partial relaxation of the COVID-19 measures led to a gradual increase in NO2. In China, it took only 2 months to reach the NO2 levels of 2019, whereas in many other cities around the world, NO2 columns remained lower than in 2019 for more than 4 months. 

In Europe and North America, the emergence of a second COVID-19 wave and the subsequent tightening of the restrictions in October 2020, led to new NO2 reductions, which are however still relatively weak compared to the first pandemic wave.

Great deal of attention for impact of coronavirus on NO2 pollution

Our results were published in peer-reviewed scientific literature (Bauwens et al.: Impact of coronavirus outbreak on NO2 pollution assessed using TROPOMI and OMI observations, Geophys. Res. Lett., 47, e2020GL087978,  https://doi.org/10.1029/2020GL087978, 2020) and in press releases like:

The topic attracted a great deal of attention from the local and international media:

Ongoing work on anthropogenic pollutants

This research is ongoing. The unanticipated atmospheric composition experiment caused by the pandemic constitutes a unique opportunity to test our understanding of atmospheric processes driving the abundance of anthropogenic pollutants.

Ongoing modelling work is being conducted in order to disentangle the impact of COVID-19 from the effects of meteorological variability and long-term emission abatement policies. 

Averages of NO2 columns in 5 regions
Figure 1: The upper panels show the 28-day running averages of NO2 columns observed by TROPOMI in a 25×25km cell around all cities with > 300.000 inhabitants. The number of cities used to calculate the averages is given between brackets for each region. The lower panels give the relative decrease in NO2 in 2020 compared to 2019. The orange lines indicate the start a period of tighter restrictions ; note that this date is often not the same for all cities within a region, and that the line is thus an approximation.
Background image credit: Sophie Bailey.