Air pollution is a silent and insidious killer the world over. Today, 9 out of 10 people breathe air containing high levels of pollutants, and the consequences are more deadly than war, violence, and many diseases.
A new analysis on global air quality between 2010 and 2016 has found that over half the world's population was exposed to increased levels of fine particulate matter, which can find its way deep into the lungs and even the bloodstream, causing all sorts of health and developmental issues.
Nor is that burden falling equally. During the study period, the average individual in North America and Europe was exposed to less air pollution, whereas people in Central and Southeast Asia experienced on average the highest concentrations of fine particulate matter in the air.
While some progress has been made towards cleaner air in wealthier regions, that's barely put a dent in the larger problem.
"While long-term policies to reduce air pollution have been shown to be effective in many regions, notably in Europe and the United States," says Gavin Shaddick from the University of Exeter, "there are still regions that have dangerously high levels of air pollution, some as much as five times greater than World Health Organization guidelines, and in some countries air pollution is still increasing".
Oftentimes, when we think of air pollution, we imagine a smog-filled city, but these new findings suggest urban and rural areas are both facing unsafe levels of fine particulate matter.
Using satellite and ground-based data, the study examined trends in global, national and regional air quality over the course of seven years, against a backdrop of clean air efforts.
In rural areas of Central and Southern Asia, they found population-weighted concentrations of fine particulate matter rose by approximately 11 percent.
In India, where nearly 70 percent of the population lives in rural areas, this is fast becoming an emerging health crisis.
"The problem, and the need for solutions, is not confined to cities," the authors write, "across much of the world the vast majority of people living in rural areas are also exposed to levels above the guidelines."
The same can be said in parts of Northern and Sub-Saharan Africa, where less dense communities may actually be more at risk.
In large part, the authors explain, this is being driven by dust and sandstorms whipped up by a rapidly changing climate - a danger we've only recently started paying attention to.
"The high concentrations observed across parts of the Middle East, parts of Asia and Sub-Saharan regions of Africa are associated with sand and desert dust," they write.
"Desert dust has received increasing attention due to the magnitude of its concentration and the capacity to be transported over very long distances in particular areas of the world."
Attempts to mitigate air pollution should therefore not only be focused on cities, but on the planet as a whole.
Air pollution, after all, doesn't adhere to city, state or national boundaries, and even in high income countries, it can be widespread and dangerous, especially for low-income communities, the elderly, and children.
Last year, for instance, research found air pollution had worsened in the United States in 2017 and 2018, leading to thousands of additional deaths.
Figuring out how a policy will directly impact air pollution is a difficult endeavour, Shaddick admits, but it's worth the effort given more than four million people are thought to die each year from outdoor air pollution alone.
"Attempts to mitigate the effects of air pollution have varied according to its source and local conditions, but in all cases cooperation across sectors and at different levels, urban, regional, national and international, is crucial," the authors conclude.
It's true the current pandemic has been decreasing air pollution and saving lives, but at the same time, it's also true that air pollution is increasing the risk of dying from COVID-19.
The reality is putting already vulnerable communities at even greater risk, simply because of the air they breathe. Something clearly has to change, or the silent pandemic of air pollution will continue to kill us in ever-increasing numbers, even when this viral pandemic is over.
The study was published in Climate and Atmospheric Science.