An invisible crisis: Ranking the world's most polluted countries

In a landscape that showcases the beauty of nature, with the stunning backdrop of the snow-capped Himalayas, it seems shocking to realize that Nepal is the most polluted country in the world. Residents of this landlocked nation in South Asia are exposed to alarming levels of air pollution.

According to recent data by Oxford University’s Our World in Data platform, Nepal’s average fine particulate matter (PM2.5) levels stand at a staggering 99.73 micrograms per cubic meter (μg/m3) throughout the year. 

To grasp the scale of the problem, consider that this figure is almost twenty times higher than the World Health Organization’s (WHO) guideline limit of 5μg/m3. The pollution levels in the United Kingdom and the United States, comparatively, are significantly lower, standing at 10.47μg/m3 and 7.41μg/m3, respectively, ranking them as the 24th and ninth cleanest countries.

The top five most polluted countries 

The data, collected in 2017, reports PM2.5 levels for 195 countries worldwide. Following Nepal, Niger and Qatar are the second and third most polluted countries, with respective concentrations of 94.05μg/m3 and 91.19μg/m3. The researchers noted North Africa’s high levels of pollution, attributing the issue in part to the region’s dry conditions and abundance of dust and sand sources.

India, with a staggering population of 1.4 billion, and Saudi Arabia also fall in the top five, with PM2.5 exposures of 90.87μg/m3 and 87.95μg/m3 respectively. Excluding Qatar, PM2.5 levels in each of the top five countries have increased since 1990, indicating that efforts to reduce pollution have been unsuccessful in these nations.

Dr. Raj Tiwari, an assistant professor in Climate Change Data Science at the University of Hertfordshire, expressed deep concern over these findings. “Countries like Nepal (South Asia), Niger (Africa), and Qatar (Middle East) are on the top end for PM2.5, with an exposure of more than 90 – which is very alarming,” said Dr. Tiwari.

The smallest increase in PM2.5 levels among the top five was witnessed in Nepal, with a leap of 12.13μg/m3. The list of the countries with the poorest air quality also included Egypt, Cameroon, Nigeria, Bahrain, and Chad.

Contrasting these high pollution levels, Finland logged the lowest PM2.5 mean annual exposure at 5.86μg/m3, although still slightly exceeding WHO’s safety levels. Brunei, New Zealand, Sweden, Canada, and Iceland also reported relatively low levels of the harmful PM2.5 particles. However, these figures remain above the WHO’s recommended safety levels, highlighting the global scope of the air pollution problem.

Air pollution and mortality rates

The adverse health impacts of air pollution are starkly portrayed by the national death rates linked to outdoor air pollution in 2019. Despite Nepal reporting the highest PM2.5 levels, it was Uzbekistan, a Central Asian country with a population of 20.5 million, that haf the most significant fatality rate. The country registered 179 deaths per 100,000 people due to air pollution, a more than twofold increase from the 81 deaths reported in 1990.

Uzbekistan was closely followed by Egypt and Qatar, which recorded death rates of 161 and 133 per 100,000 people, respectively. Considering that these countries are not the most polluted based on PM2.5 levels, the elevated death rates highlight the severe health risks associated with air pollution.

Dr. Tiwari elaborated on the role economics play in these patterns: “Further analysis on death rates from outdoor air pollution is really an eye-opener, as it clearly shows how air pollution is highly linked with the economy of the countries.”

According to the United Nations, poorer countries tend to have less stringent air pollution laws, lower vehicle emission standards, and higher numbers of coal power stations. Such factors contribute to the higher levels of pollution and subsequent health impacts seen in these countries.

In stark contrast, Finland, the country with the world’s lowest PM2.5 exposure, also reported the lowest number of deaths due to pollution exposure, with just three deaths per 100,000.

However, even as air pollution exacts a significant toll on public health, it is not the leading cause of death globally. The Global Burden of Disease study, published in The Lancet, reported that high blood pressure was the leading cause of death in 2019, accounting for 10.85 million fatalities, closely followed by smoking, which was responsible for 7.69 million deaths.

More about fine particle pollution

PM2.5 are particles less than 2.5 micrometers in diameter, so tiny that they’re about one ten-thousandth of an inch. These particles can be composed of various materials, including dust, soot, metals, and harmful chemicals. Emissions from vehicles and industrial facilities, particularly those burning fossil fuels, are the primary sources of such pollutants.

Due to their extremely small size, PM2.5 particles can be inhaled deep into the lungs, causing long-term damage. A wealth of scientific evidence has linked long-term exposure to these particles to a heightened risk of severe illnesses and premature death, primarily due to cardiovascular and respiratory diseases. 

Beyond physical ailments, air pollutants have also been tied to neurological effects, with studies showing correlations between exposure and increased risks of dementia and cognitive decline.

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