Coronavirus has been holding the world’s throat with clenched fists since December last year.

That has resulted in drastic measures taken by governments to protect their citizens.

Among those measures, lockdown, which Rwanda adopted on March 21 induced by physical distancing has proven to be efficient in curbing the spread of the virus.

Regardless of its economic and mental health impacts, the lockdown might be improving the air quality, according to Rwanda Environment Management Authority (REMA).

"Reduced vehicle emissions as a result of banning unnecessary movements of people during this lockdown has yielded greater air quality,” said Dr Egide Kalisa, the Air Quality Specialist at REMA.  Kigali, he added, recorded a decrease of more than 20 per cent for PM10 and 13 per cent for PM 2.5.

With motor vehicles emissions as one of their primary sources, PM 10 and PM 2.5 are particulate matter generally described as fine particles with 10 and 2.5 micrometres or less in diameter present in air and exposure to them is very harmful to human health. 

For instance, PM 10 mostly trapped in the nasopharyngeal tract can lead to asthma and bronchitis whereas PM 2.5 are much smaller and more hazardous as they can reach the lungs thus leading to lung cancer among other respiratory complications.

To put this into context, the data collected after one week at Kigali Ambient air quality reference station showed that there was a decrease from 69 to 55 microgram per cubic meter for PM10 and 33 to 29 microgram per cubic meter for PM2.5 in an analysis conducted by the specialist for a week before and after the lockdown.

According to the analysis, the lowest peaked emissions are between 12-4PM whereas the highest peaked are between 4-8AM and 5-8PM which Dr Kalisa linked to the times with most or least traffic on roads.

"Generally, we have more emissions in the wee hours of the morning and early in the night and they decrease within the day,” remarked Dr. Kalisa adding that business begins at those early hours which prompts movement of people as well as vehicles and peaks in the morning rush hours.

The same case, Kalisa pointed out, applies for the early night hours when people are going home from work whereas during the day there is minimal movement, for people are busy with their daily undertakings.

Under normal circumstances, PM 2.5 122.9 micrograms for working days and 83.0 for no-workdays (public holidays, car free day and weekends), whereas PM 10 143.6 micrograms for work days and 99.5 micrograms for no-work days, showed a study on Characterization and Risk Assessment of Atmospheric PM2.5 and PM10 Particulate-Bound PAHs and NPAHs in Rwanda, Central-East Africa conducted by Kalisa and his peers in 2018.

The WHO air quality guidelines stipulate that PM 2.5 and PM 10 shouldn’t exceed 25 and 50 microgram per cubic meter respectively in a 24 hour period.

According to WHO’s air quality assessment, 92 per cent of the world’s population lives in places where air pollution levels exceed the WHO guideline limits, resulting in the deaths of seven million people every year