Following the guidelines that were introduced by the government of Uganda to contain the novel coronavirus outbreak, where a nationwide shutdown was declared by the President putting restrictions on the movement of people and a ban on all public and private vehicles except for a few permitted ones.
The lockdown has provided a very rare opportunity to examine what happens to air quality when there’s a drastic reduction in travel and many suspended business operations according to researchers.
AirQo that did the study believes that as much as all efforts go to addressing the COVID-19 pandemic, attention should be paid to resulting consequences such as the impact on air pollution and learn what actions could be taken to sustain clean air for our cities when the situation returns to normal.
The study looks at the immediate but unintended impact of the lockdown on air quality levels in the greater Kampala.
It analysed air quality (fine particulate matter — PM2.5 ) data from the AirQo air network and the reference monitor at the US Embassy in Kampala.
7 locations in greater Kampala were selected: Nsambya (US Embassy), Civic Centre, Bugolobi, Seguku (2), Bweyogerere, & Kiwafu (Entebbe). We compared air quality for the lockdown period (18th March to 4th April) with the preceding two weeks (4th -18th March).
It also looked at historical results for the same days in 2019. They finally examined 1-year seasonal longitudinal variations.
Nsambya and to a lesser extent Bweyogerere and Bugolobi, for example, showed the morning rush hour between 6 am and 9 am as a high peak time before lockdown while after the restrictions the peak is almost unidentifiable.
On average this represents a reduction in air pollution of around 60% during the morning rush hour.
However, in those locations in the evening, there is little difference between a lockdown and the period before. This suggests that the morning peak is caused by vehicle traffic while the evening emissions relate more to domestic fuel use although confirming this requires more investigation.
In Seguku on the Kampala-Entebbe road, researchers saw little variation with a substantial peak.
One possible explanation is that the monitoring location is located along the national trunk road that connects Kampala and Entebbe municipality including the airport with considerably heavier traffic than most of the regular major roads, and comparing with an adjacent location (Seguku-Lubowa) would, to a great extent validate this assumption.
Similarly, there is a drastic drop in the daily pollution levels during the lockdown from the period leading to the lockdown, starting 19th March following official closure of public gatherings.
Further preliminary validation with historical comparisons for the same days of 2019 confirms that the drop in pollution levels is particularly unique to this period, which was about 40% reduction in the daily mean from the two weeks leading to the lockdown, and about 51% reduction for the same days in 2019. for the same days in 2019.
“However with time, we can see that pollution levels begin to rise, perhaps as the initial strict adherence to the restrictions begin to wear off. This coincided with a period of lower pollution levels in 2019 in early May possibly as a result of increased rain,” noted researchers.
Understanding the key drivers
Influence of traffic and road network
Any visitor to Kampala will notice firsthand the high levels of traffic congestion across the city. The public transport network is not as efficient as it should be and largely filled by ageing taxis and boda boda which clog the streets along with a wide range of private and commercial vehicles.
Further still, while the government is prioritizing paving and improvement of the road infrastructure, about 70% of roads in Kampala still remain unpaved which adds to the immediate sources of particulate matter from loose surfaces.
Government implementation of the lockdown measures meant most vehicles and all other automobiles were taken off the road.
Domestic fuel burning
This is often cited as one of the main contributors to poor air quality in sub-Saharan Africa, especially in residential areas.
More than 90% of households in Uganda still use solid biomass (charcoal and firewood) for cooking and heating and yet these have very high pollution intensity.
It would be particularly interesting to investigate pollution levels in predominantly residential areas, especially in this lockdown period to contextualize the impact of domestic activities on local pollution.
Uganda has two wet seasons and two dry seasons in a year. The first wet season runs from March to May while the second from September to November.
The lockdown came towards the end of March, a time where Uganda is transitioning from dry season to a wet season.
There is a definite trend to higher levels of PM2.5 in the dry season and lower levels in the wet season when there is a stronger suppression effect by rainfall.
The fact that pre-lockdown pollution levels were generally lower than the same days in 2019 also confirms that weather changes could have influenced the improvement in air quality, but that the lowest pollution level was recorded for only one day in November 2019 underscores the contribution of the drastic social distancing measures towards air quality improvement.