In many cities, concentrations of some pollutants declined while others increased. But Jakarta, Indonesia, was the only one that saw a statistically significant improvement in overall air quality as a result of governmental policies.
Improvement is relative as Jakarta still has a severe air pollution problem, but the trends there pointed to how effective targeted policies could be at reducing pollution. The city has emission standards for vehicles, the researchers noted, and saw a decrease in nitrogen dioxide, which is associated with vehicle exhaust. But it does not have limits on biomass burning, such as burning land to clear it after a harvest, and it saw increased concentrations of ammonia, which is associated with such agricultural activities.
Overall, however, the researchers found that most of the increased pollution was driven not by biomass burning but by sources like traffic and fuel burning — a distinction the researchers were able to make because biomass burning shows up in satellite observations in intense but relatively short bursts, usually with a seasonal pattern. Other human activities produce less intense but more sustained pollution.
“Open burning of biomass for land clearance and agricultural waste disposal has in the past overwhelmingly dominated air pollution in the tropics,” Karn Vohra, a research fellow at University College London and the lead author of the study, said in a statement. “Our analysis suggests we’re entering a new era of air pollution in these cities, with some experiencing rates of degradation in a year that other cities experience in a decade.”
The study does not answer the question of what activities, specifically, are most responsible.
“The driver of these trends is anthropogenic activity, but that’s very broad — there’s so much anthropogenic activity that takes place within a city,” Dr. Marais said, adding that further scientific research was needed to identify the largest contributors.
Then, she said, it would be up to policymakers to do cost-benefit analyses and determine the most effective and economically viable ways to reduce pollution.