May 22 (Mongabay) COLOMBO— The COVID-19 pandemic has sent half the global population into some form of lockdown. Factories have closed, streets and highways lie empty, restaurants no longer serve customers.
Sri Lanka, like most other countries, has imposed strict measures to contain the spread of the virus. And like in many other countries, the sweeping halt in activity has had a tangible impact on pollution.
The government imposed an almost total island-wide lockdown from March 20 that lasted throughout April and into May. During that period, air pollution indexes have improved, particularly in urban areas like Colombo, where vehicle exhaust emissions account for most of the pollution.
Monitoring stations run by the Central Environment Authority (CEA) and the National Building Research Organisation (NBRO) recorded a sharp drop in concentrations of small particulate matter (PM2.5 and PM10) after the lockdown compared to a week before it was imposed, aligning with the mobility restrictions and curfews that came into force.
An NBRO monitoring station in the heart of Colombo recorded a 75% drop in PM2.5 and 65% in PM10 levels, including the lowest 24-hour average within 20 years. The air quality index (AQI) tracked by the U.S. Embassy in Colombo shows a similar trend of improved air quality: April 2020 had an overall average AQI of 52.1 in Colombo, 27% lower than April 2019 and 28% lower than April 2018.
Air quality has improved not only compared to previous years but also to previous months. The April AQI measured by the U.S. Embassy was half the level measured in February, highlighting a clear decline in overall emission levels.
“In Sri Lanka, air pollution is mainly concentrated in urban areas, and more than 60% of our urban air pollution is due to vehicular emissions,” said Sarath Premasiri, a senior scientist at the NBRO. Peaks in air pollution correspond to the morning and evening rush hours, so “If vehicle traffic is low, we expect low levels of pollutants,” Premasiri said.
Other major sources of air pollution are industrial activity, mining, coal- and diesel-fired power plants, domestic activity, burning of agricultural residue, and the traditional slash-and-burn farming method known as chena.
“Most industries and commercial enterprises have also stopped their activities, which minimizes wastewater and solid waste generation and reduces methane, H2S, and other related air pollutant emissions,” Premasiri said.