Fewer cars on the road due to COVID-19 restrictions led to a drop in one pollutant but caused another to rise, according to a University of Malta study.
The pandemic saw half the usual traffic on the roads when compared to 2019, resulting in a reduction in nitrogen dioxide (NO2) across Malta.
"On easing the restrictions on June 15, 2020, traffic started to increase steadily and reached the 2019 levels by October 7 when schools reopened," the study observed.
However, while NO2, a pollutant emitted by car vehicle exhaust, decreased in the traffic-heavy localities of Msida (54 per cent) and Żejtun (57 per cent), ground-level ozone (O3) in these areas rose.
In Msida, an increase of up to 61 per cent in O3 was noted during the partial lockdown, compared to the business-as-usual scenario, while in Żejtun, a 20 per cent O3 increase was observed in September 2020.
In the quiet Gozitan town Għarb, ozone decreased by up to 11 per cent when compared to a business-as-usual scenario.
Ground-level ozone is created when nitrogen oxides and volatile organic compounds emitted by stationary cars, power stations and other sources combine with sunlight.
Breathing in high concentrations of ozone can be damaging to respiratory health, as it can reduce lung function and harm lung tissue.
The study illustrated that strategies to reduce a pollutant such as NO2 needed to take into consideration the inevitable altering of atmospheric chemical balance that could spur increases in other pollutants such as ozone.
“Thus, in a future where [these] emissions are targeted to decrease by similar levels to those observed during the pandemic, there will be an increased burden to control ozone levels.
Therefore, policies should focus on limiting ozone precursors which are not routinely measured across Europe.”
Researchers also noted that the all-cause mortality from exposure to a daily one-hour nitrogen dioxide concentration was 0.9 per cent lower in April and May 2020, compared to a scenario without the pandemic.
The study, which was authored by academics Noel Aquilina, Sara Fenech and Ryan Vella, was published in the journal Frontier.