Kampala Air Quality improves by up to 40% during the Covid-19 lockdown

Following the recent guidelines introduced by the government of Uganda to contain the novel coronavirus outbreak in the country, a nationwide shutdown was declared by the President on the 30th March 2020, putting restrictions on movement of people and a ban on all public and private vehicles except for a few permitted ones for 14 days to prevent the spread of COVID-19.

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.

At AirQo we believe that as much as all efforts now go to addressing the COVID-19 pandemic, we must also pay attention 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. Therefore in this article, we look at the immediate but unintended impact of the lockdown on air quality levels in the greater Kampala.

We analysed air quality (fine particulate matter?—?PM2.5) data from the AirQo air monitoring 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). We also looked at historical results for the same days in 2019. Finally we examined 1-year seasonal longitudinal variations.

Key insights from the air quality analysis

Pollution variations over the 24-hour period from 18th March to 4th April 2019 and 2020

In each of the charts seen above, the hourly air pollution means for the two weeks prior to lockdown remain substantially above the hourly means recorded during the lockdown period but with some interesting variations according to location. Nsambya and to a lesser extent Bweyogerere and Bugolobi, for example, shows the morning rush hour between 6am and 9am 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 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, we see 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.

Daily variations from 4th March to 4th April 2019 and 2020

Similarly, we notice 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.

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.

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 prioritising 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 lock down 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 contextualise the impact of domestic activities on local pollution.

Meteorological factor

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. As the above charts show 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.

1-year longitudinal datasets showing seasonal variations in pollution levels

US Embassy Monitoring Station

Civic Centre Monitoring Station

The general slow-down of pollution generating activities from traffic to industry in the current circumstances could have had a strong immediate impact, but understanding pollution levels go beyond just the immediate sources. There are a wide range of additional factors that influence air quality levels. Obtaining an in-depth understanding of all these aspects requires more comprehensive investigations for conclusive insights, most importantly to quantify source-level contributions, including industries which were not included for this initial analysis.

It is also noteworthy that while air quality noticeably improved during the lockdown, some daily levels have still been above 25µgm-3, what WHO considers to be acceptable, and the 1-year longitudinal datasets even indicate much stronger outstrip of the WHO annual limit of 10µgm-3.

This is an ongoing and evolving study, we will continue to undertake further analysis of the impact of the COVID-19 lockdowns and share our findings in the coming weeks.