In many cities, the 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 government policies.
The improvement is relative because Jakarta still has a serious air pollution problem, but trends there indicate how effective targeted policies can be to reduce 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 has no limits on burning biomass, such as burning land to clear it after harvest, and it showed 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 from sources such as traffic and fuel burning – a distinction the researchers were able to make because biomass burning appeared in rapid but relatively short bursts in satellite observations. , usually with a seasonal pattern. Other human activities produce less intense but more persistent pollution.
“Air pollution in the tropics has become very high before biomass is burned for land clearance and agricultural waste disposal,” said study lead author Karan Vohra, a research fellow at University College London, in a statement. “Our analysis shows that we are entering a new era of air pollution in these cities, with some experience rates of decline in a year that other cities experience over a decade.”
The study does not answer the question of which activities, in particular, are most responsible.
“The driver of these trends is anthropogenic activity, but it is very widespread – there is a lot of anthropogenic activity within a city,” Dr Marais said, adding that further scientific research was needed to identify the biggest contributors.
Then, she said, it would be up to policymakers to conduct a cost-benefit analysis and determine the most effective and economically viable ways to reduce pollution.