Visualizing air pollution across the world

On April 7th of every year, the World Health Organization commemorates World Health Day to raise awareness of a health challenge of global concern. This year, they’re campaigning on the theme of “Our planet, our health”. Air pollution has come to the fore in recent years when discussing environmental influences on health. New data from the World Health Organisation shows that 99% of the global population breathes air containing pollutant concentrations exceeding their guidelines for good health. So today, we’ll explore the global distribution, causes, and effects to better understand one of urbanization’s most harmful consequences.

How do we measure air pollution?

For decades, international agencies have focused on two types of polluting matter when measuring air pollution: PM2.5 and PM10.

The “PM” stands for “particulate matter”and these two particle types are respectively less than 2.5 and 10 microns in diameter – both smaller than the width of one human hair. PM2.5 is harmful in the short-term, leading to adverse consequences in vulnerable groups such as children and older adults. PM10, however, is more harmful with repeated, chronic exposure, especially to people with pre-existing lung conditions. You can read more about these pollutants here.

How is air pollution geographically distributed?

Given that PM2.5 is more harmful to human health in the short-term, this blog post will focus on this type of air pollution, which is measured in units of micrograms per cubic meter of air. First, the below map displays mean annual exposure levels to PM2.5 across the world in 2017. Exposure is more severe in South Asia and some parts of Africa, especially the Middle East.

What factors are linked to more air pollution?

Now that it’s clear where PM2.5 levels are most concerning, we wanted to know why this is the case. One explanation might be countries’ economic standing, which can be measured by GDP per capita. Here’s how these two factors are related:

The relationship between GDP per capita and pollution levels is not clear. On one hand, some countries who have modernized rapidly are experiencing greater pollution than ever before, whereas others have managed to cut back on these harmful substances through policy and legislation. Read more about this complex relationship here.

What are the health effects of air pollution?

It’s no surprise that PM2.5 impacts lung health, but researchers have also suggested it increases all-cause mortality (read more here). Here are two scatter plots linking PM2.5 levels and mortality for both sexes.

In general, countries with higher PM2.5 levels also have higher mortality rates. This relationship is similar across sexes, although it exists more strongly for females. However, other factors like infant mortality, healthcare quality, and the prevalence of deadly infectious diseases in each country’s population may have a strong impact on these mortality figures, too. Nevertheless, it’s difficult to discount the influence of air pollution on mortality, especially when researchers have discovered evidence in favor of this association.

How have PM2.5 levels changed over time?

In order to understand the future of air pollution, we have to look to the past. The World Bank has published data on global PM2.5 levels between 1990 and 2017 (the latest figure), so here is a slope chart visualizing changes during the period in between.

Countries at different ends of the air pollution rankings have made different amounts of progress. A general stability in PM2.5, however, does provide us with optimism; it means that as countries urbanize, huge jumps in pollution have been mitigated. As more people begin to inhabit the world’s cities, this trend is one that has to continue. What does “Our planet, our health” mean to you? And what stories can you tell from your own experiences of environments that are supportive or detrimental to your wellbeing? We’d love to hear from you! In the meantime, happy #WorldHealthDay.