The impact of COVID-19 on air pollution and traffic in Catalonia
Paper summary
Link to Paper 10.1007/S11356-021-17137-7/TABLES/5
Research Goals
This post looks at a study published in the Environmental Science and Pollution Research Journal. In this work, Gorrochategui et. al are focused on understanding the impact of COVID-19-related lockdowns on air pollution and traffic across Catalonia, Spain. The research goals for this study can be summarized as follows:
Model the change in air pollution levels across Catalonia, Spain before, during, and after a major COVID-19 lockdown period in 2020.
Compare air pollutant levels with individual-level mobility data to better understand the relationship between the two variables.
Examine the differences in satellite remote sensing columns for nitrogen dioxide and ozone.
Examine the difference in meteorological parameters during the pandemic period and compare it with previous years. This was done to understand the meteorological impacts on air quality, which should not be discounted.
Data Sources
The air pollution data were from a regulatory monitoring network in Spain. The pollutants studied were particulate matter, ozone, and nitrogen dioxide.
The mobility index parameter maps out the change in human mobility compared to a reference value. The reference value is a five-week mean from January 2 to February 6 before the lockdown.
Traffic density data were from the General Directorate of Traffic (DGT)
Climate data were from the Meteorological Service of Catalonia (Meteocat)
Satellite remote sensing data from the TROPOMI instrument were used to model the change in nitrogen dioxide and ozone (TROPOMI does not provide data for particulate matter).
Major Takeaways
They examined the change in each of the three pollutants in April 2020 with the same period in 2019 and 2018. Like many other studies, they saw a reduction in nitrogen dioxide and particulate matter. When looking at TROPOMI data, they found a 57% decrease in nitrogen dioxide when compared to the five weeks before the lockdown. They found that ozone column concentrations increased from 2019 levels, which is consistent with other research conducted in the area (a percentage change in ozone was not provided).
They looked at the change in traffic volumes during two COVID-19 lockdown periods: period 1 (the strictest lockdown period) and period 2 (the ‘new normal). For each traffic type review, a reduction was found. The reduction in traffic volumes ranged from 12% to 82% from 2019 levels.
When looking at meteorological data, they found that April 2020 (the strictest lockdown period) had a higher average temperature and humidity compared to 2018 and 2019 levels. Interestingly, the rain in April 2020 was 454% of the average for that month, achieving a historical record.
Finally, when comparing the relationship between mobility index and air pollution, they found a 100% reduction in retail and recreational activities during the April lockdown period.
The mobility index had a positive Pearson’s R with nitrogen dioxide and particulate matter, and a negative Pearson’s R with ozone. The statistical significance of these values was not provided.
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