- The lockdown on traffic and industry imposed by the Sri Lankan government in response to the COVID-19 pandemic coincided with a period of improved air quality, especially in Colombo.
- But the popular perception that the lockdown led to the im-provement ignores a much more important factor, says envi-ronmental scientist Lareef Zubair: a seasonal change in wind di-rection bringing clean, fresh air from the Indian Ocean.
- Air quality in Colombo continues to be influenced largely by transboundary transport of air pollution from the Indian sub-continent and Southeast Asia; forest, scrub and agricultural res-idue burning; poor solid waste management systems; and the Norochcholai coal power plant located in Sri Lanka’s northwest.
- This post is a commentary. The views expressed are those of the author, not necessarily Mongabay.
There has been much media hype about improved air quality in Sri Lanka, and particularly in the island’s commercial capital, Colombo, during the COVID-19 lockdown phase.
However, a close examination of the available air quality data shows that there was no improvement in air quality immediately after the imposition of the curfews except for suspicious outlier stations whose drop predated the curfews by a week.
The improvement in air quality only began one week later, after the reversal in wind seasonality, as the northeast trade winds gave way to southwest trade winds. Such a reversal occurs each year in early April. Even then, the drop in air quality indexes remained around 30% only.
As the wind reverses, it brings in pristine air from the southern Indian Ocean to Colombo rather than from Sri Lanka’s northern landmass and the lands to the north. After April, the pollution from these sources are directed to the interior of Sri Lanka and beyond, but not toward Colombo.
Understandably, there was a drop in vehicular emissions in Colombo, thermal power plants and a few other industrialized and urbanized localities due to COVID-19 curfews.
The celebration of a significant improvement in air quality is misplaced and should not distract pollution mitigation focus from the coal power plants, the agricultural residue burning, forest and garbage fires, and the industries that continued to function.
A host of mainstream media reports and and social media posts have attributed the recent improvement in air quality to the curfews imposed since March 20, introduced to control the COVID-19 transmission. These reports seem to follow news in locations such as Southern California or in Central China, where pollution levels dropped by 70%.
However, the casual surmise that if one shuts down traffic and closes down the majority of industries, we are most likely to lose sight of the role of pollution from other sources such as transboundary pollution, particularly from the Indian subcontinent, forest fires, garbage incineration, agricultural residue burning, the questionable Norochcholai coal power plant in the northwest, and all industries that continued to function despite the lockdown.
The relative contributions of these sources vary by place and time. We make use of the available observations of air pollution to address the questions of the extent of the drop and whether it was only the lockdown of traffic and urban activity that led to the drop.
Measuring air pollution
There are a growing number of air pollution measuring stations in Sri Lanka that observe air quality through measurements of particulates, noxious gases, aerosols and heavy metals. Of these, the amount of fine particulates measuring 2.5 microns (PM2.5) or other pollutants such as ozone (O3) and nitrous oxides (NOx) are key variables and are used to calculate the air quality index (AQI).
In Sri Lanka, the Central Environmental Authority (CEA), National Buildings Research Organization (NBRO), U.S. Embassy, National Institute of Fundamental Studies (NIFS), and the Federation for Environment, Climate and Technology (FECT) measure PM2.5. The air quality instruments at the U.S. Embassy in Colombo are the most reliable at present.
If one compares the U.S. Embassy measurements for PM2.5 the week before and after the curfew (March 20), there is no perceptible drop. One sees the same with most other instruments as well. If one compares the PM2.5 to two to four weeks before and after, then there is a drop off of around 30% — significant, but not overwhelming.
Between February and April 2020, there was a drop in PM2.5 of 50%, which is sometimes presented as evidence of the dominant role of the curfews. However, such a comparison includes the influence of the intervening seasonal wind reversal. The reversal in wind directions in April shuts down pollution transport to Colombo from most sources. There was a similar large drop-off from February to April in 2018 and 2019, as shown in the chart above.
From November to March, the wind comes from the north and east, carrying with it pollutants from the Indian subcontinent and Southeast Asia. As the air tracks over the Sri Lankan landmass, it adds to this pollution from the Norochcholai coal burning, forest fires, agricultural residue, garbage burning and other industries.
From April to September, the wind reverses so that on average the wind direction is coming from the south and west over the pristine atmosphere of the Indian Ocean. Even though the air pollution drops in Colombo from April to September, the wind reversal takes the pollution from the western coast to the rest of Sri Lanka. Persuasive studies from the universities of Peradeniya and Sabragamuwa show that the forest dieback in Horton Plains is tied to an increase from April to October of lead contamination in the soil.
Daily variability in wind trajectories
While the seasonal variability in wind patterns has been described so far, there is day-to-day variability that affects the details of local pollution. Based on observations of wind, we have computed trajectories of air that reached Colombo on each day before, during and after the curfews. The accompanying maps show such trajectories for the two days with the highest and lowest AQI during the curfews. These maps show that on the days when the wind comes from north and east, air pollution is twice as high as when it comes from the south and west.
Multiple sources of air pollution
Traffic and the shutdown of industries can contribute significantly to air pollution, but these are secondary to the combined effect of other factors whose roles are manifested by the wind reversal in April. These major sources are: transboundary transport of air pollution; forest, scrub and agricultural residue burning; poor solid waste management systems; and the Norochcholai coal power plant located in the island’s northwest.
The maps shown here indicate that there could be transport of pollution from the Indian subcontinent and northern Southeast Asia to the extent of doubling of AQI.
Previously, the perceptible rise in air pollution in Colombo from Nov. 3-5, 2019, caused much alarm. These were on days when the air pollution levels in northern India was high and when the air arrived in Sri Lanka from over New Delhi, Kolkata, the Bay of Bengal, the western coast, and over the Norochcholai coal plant.
Forests and grasslands are dry in March and there is agricultural byproducts after the end of the maha cultivation season in March. There is slash-and-burn for chena cultivation, usually in a controlled manner as a method of agriculture in marginal lands. Setting fire to dry tinder is done sometimes for short-term gain and sometimes for mischief. There is no monitoring or regulation in place, and there is little or no appreciation of the causing of air pollution, besides other impacts.
A compounding matter is the poor solid waste management systems in place and the availability of cheap cooking gas that has resulted in rural and urban dwellers incinerating unnecessarily. There is a notion among the public that releasing something into the atmosphere is a cost-free method of waste disposal.
Then there is the Norochcholai coal power plant, which spews 5 tonnes of pollutants each day into the atmosphere when it is running perfectly. But on days when the air purification equipment is defective or there are unscheduled shutdowns or startups, it can emit much more. The emissions from the plant are partially directed toward the western coast and hills from November to March and to the northwestern, central, northcentral, eastern and northern provinces from April to October.
In transition months, a significant component gets dispersed over large areas. There can be much better focus by the state plant operator and its regulators on following the environmental regulations in place.
Increasing air pollution
There has been an inexorable rise in air pollution in Sri Lanka over the past five decades. Experts have claimed that even the present levels of air pollution could lop several years off the life expectancy of both humans and animals.
The efforts of the regulatory institutions has not reversed the decline in air quality or adequately monitored it. The emissions testing for vehicles has helped, but transport still remains a major contributor to poor air quality.
The curfews in Sri Lanka and in the larger region contributed to a significant drop in air pollution. However, the role of curfews was overshadowed by the contribution of the seasonal reversal in winds. We should monitor, raise awareness among the public, and pressure lax polluters responsible for major sources of air pollution.
At a time when COVID-19 threatens our respiratory health and has overloaded the health services, especially related to respiratory ailments, monitoring and mitigation of air pollution must be both a health and a moral priority.
Mitigation options are available for other sources and should be pursued. For example, it will be a monumental blunder to add a new coal plant as coal is the worst option for emissions.
We need to learn from the promises of “clean coal” at Norochcholai 15 years ago, and the subsequent use of outdated technology, the subsequent failure to monitor regional air pollution as required in the environmental impact assessment, and the failures of the regulators just by carelessness and sometimes due to pressure on and of politicians.
On June 4, the cabinet of ministers approved the setting up of an additional 300-megawatt coal power plant with the usual platitudes about the environment in the northwestern district of Puttalam, a coastal region favored for by polluting industries for dumping and waste.
Lareef Zubair is the principal scientist at the Federation for Environment, Climate and Technology (FECT). He holds a Ph.D. from Yale University, and for the last 25 years worked as a senior lecturer at the University of Peradeniya in Sri Lanka; as a research scientist at the Institute of Fundamental Studies in Kandy; the International Research Institute for Climate and Society, New York; and the Water Center at the Earth Institute and the Department of Environmental Engineering at Columbia University, U.S.
Banner image of regular traffic congestion in suburban Sri Lanka. Following the COVID-19 pandemic, the Indian Ocean island was in lockdown for two months, a period that coincided with an improvement in air quality, particularly in urban areas. Image by Dilrukshi Handunnetti.