Air pollution has been a long-existing problem for most of the major metropolitan cities of the world. In the recent wake of the COVID-19 pandemic, there has been a renewed interest in revisiting the problem of low air quality. Several countries implemented strict lockdown measures reducing vehicular traffic and other economic activities, in order to reduce the spread of COVID-19.
In order to analyse the impact of the lockdown on air quality in Dublin, ADAPT’s summer intern, Dewansh Kaloni, working with Soumyabrata Dev at UCD, looked at the averages of one of the most common gaseous pollutants caused by automobile exhaust: Nitrogen Dioxide (NO2). These figures were gathered from one of ESA’s earth observation satellites, Sentinel-5P. Overall, they were able to notice a significant drop in the concentration of NO2 levels across Dublin owing to the lockdown measures implemented across the nation.
Ireland confirmed its first case of COVID-19 on February 29, 2020 and thereby saw growth in the number of cases continuously throughout the month of March. The number of cases suddenly rose in the middle of March, and consequently, schools and colleges were closed down to arrest the spread of the pandemic. As a result, the government imposed a strict lockdown to further curtail the spread. The lockdown was imposed on March 24, 2020 and subsequently, three days later, all ‘non-essential’ travel was banned to curtail the spread and avoid community transmission as much as possible. This presented a surprisingly great reduction in pollutant levels.
To separate out the Dublin-specific satellite data from the rest of the world, we set parameters on latitude and longitude to correspond with the city’s radius. The data files were then combined for this location over time to create a large dataset. The result was a dataset showing the nitrogen dioxide concentration levels for the area spread across the time dimension for better analysis.
The last 10 days of March 2019 recorded an average NO2 concentration of 5.489μmol/m2, whereas the last 10 days of March 2020 recorded an average concentration of 3.044μmol/m2, a drop of about 44.54%. Figure 1 shows the trend of daily average NO2 concentration for Dublin City.
Figure 1: Trend of average daily NO2 concentration for the initial period of 2019.
The average concentration for the initial 10 days of April 2020 recorded 3.072μmol/m2, which indicated towards the similar trend of drop in NO2 concentration post lockdown. Figure 2 clearly shows that concentration continued to drop after lockdown. The calculated average concentration of NO2 for April 2019 was 7.075μmol/m2 whereas for April 2020 it was 3.831μmol/m2, recording a significant drop of 45.8%. The major improvement in NO2 concentration was because of the strict lockdown imposed in Dublin for the month of April. The timeseries plot for 2019 and 2020 clearly shows the drop in NO2 concentration after lockdown was imposed on March 4th in comparison to the same period in March 2019.
Figure 2: Trend of average daily NO2 concentration for the initial period of 2020. We show the lockdown period in green color.
Finally, we also show the daily average concentration plotted over Ireland’s map via this GIF animation in Figure 3. The entire country observed a noticeable drop and the plot improved with respect to Nitrogen Dioxide concentration for March 28-30 (Concentration of Nitrogen Dioxide in the atmosphere is spread over the colour range; darker red indicating a higher concentration), as compared to the previous days.
Figure 3: Tropospheric vertical column of nitrogen dioxide over the entire country of Ireland from 22-Mar-2020 till 30-Mar-2020.
Such remote sensing analysis techniques can be beneficial for monitoring the atmosphere in regions of the earth which lack ground-based monitoring stations with zero new installments. The COVID-19 lockdown brought a rare opportunity for researchers to see the direct impact that lower levels of emissions can have on the air quality, even over a relatively short period of time, and thereby equpiing them to influence policymakers to implement stricter environmental laws.
This work is done by Dewansh Kaloni as a part of the summer internship at the ADAPT SFI Research Centre, University College Dublin, Ireland. Dewansh Kaloni is a third-year undergraduate student at Birla Institute of Technology and Science, Pilani, India. He is currently a summer intern working with Soumyabrata Dev, and is hosted at the THEIA: THE visIon and Analytics lab, University College Dublin. His areas of interest include deep learning and remote sensing. This is a collaborative work with researchers from Nanyang Technological University Singapore.
 This research work is currently under peer-review process: D. Kaloni, Y. H. Lee, S. Dev, Impact of C19-induced Lockdown on Air Quality, under review.
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