Transboundary air pollution the zero-sum blame game and what might help instead

Between January 2019 and now, fine particle pollution levels in Colombo have been “Unhealthy” or worse about 5% of the time between the months of October and March. There were five instances where it happened on successive days and on one of those occasions, 3 days in a row (November 17-19, 2022). Were all these days influenced by transboundary pollution? The author conducted a qualitative assessment of weather patterns, air quality measurements around South and Southeast Asia, and satellite data products on such days, to identify common features of the most severe pollution events affecting us. The path that air travelled en-route to Colombo on each of those days was mapped with an air trajectory analysis tool. 

In broad terms, the confluence of a large low-pressure system in the Bay of Bengal and lighter winds over the island during the northeast monsoon are most conducive for these high pollution events. Most often, polluted air masses of Indian origin hovering over the ocean act as a large reservoir of additional pollution that “leaks” in our direction when winds line up correctly. The specifics are important, as not all low-pressure systems cause this behaviour. If winds are strong enough, both distant and local pollution would be diluted. Sometimes air travelling over northern India, Bangladesh, Myanmar or Thailand gets mixed in, but more distant source regions usually contribute less to our pollution, since air has more time to get diluted. In one instance, air rotated clockwise around a giant high-pressure system over India, only to get caught up in the northeast monsoonal winds and take aim at Sri Lanka. 

There have undoubtedly been days where air quality was not as bad, but transboundary pollution still played a role. However, it is extremely challenging to determine how much additional pollution regional countries would have contributed to our own locally generated pollution on a given day. Though the above-mentioned tools can confirm if air travelled through polluted regions, they do not shed light on exactly when or how much extra pollution the air picked up along the way. Answering such quantitative questions is a much more involving technical exercise. 

We don’t have the luxury of dismissing this as scientific mumbo-jumbo. Even if we did, we still have to breathe the same polluted air as everyone else. Billing big brother for damages is just an entertaining political stunt that will get us nowhere. We can try, but our complaints alone aren’t going to motivate any of our neighbours to clean up any faster. Until such time, as efforts to reduce transboundary pollution come to fruition and air pollution in South Asia is reduced substantially, we will have to co-exist with these high pollution episodes. Here are a few ideas for taking the edge off such events: 

• Everyone agrees to the fact that permanently reducing pollutant emissions is tough and takes time. For starters, what if we reduced our own local emissions on targeted days when transboundary events are expected? Since the most severe episodes haven’t lasted more than three days, it is not terribly burdensome to require people to postpone practices like backyard burning a few days when such an episode is on the horizon. And if burning is unavoidable, it must be restricted to between approximately 10AM and 3PM, when atmospheric dispersion is at its maximum. 

• This also requires forecasting such pollution episodes at least one day in advance. Currently, we only get notified during or after an event has occurred. Air pollution forecasting tools of varying levels of sophistication already exist online, but we need to invest in our own tools and train up more air quality forecasters and analysts. 

• This information could be disseminated to the public through daily TV weather reports, providing necessary forewarning. 

• Might some offices and schools consider asking some of their staff and students to work and learn remotely on those days, to reduce vehicle emissions? 

• As always, take steps to minimize exposure to bad air by reducing time spent outdoors on polluted days, using air purifiers indoors, running car A/Cs in recirculation mode or wearing N-95 masks.