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When it comes to air quality, almost nobody on Earth is safe, according to a new study.

We are constantly breathing in fine particulate matter detrimental to our health in nearly every place across the planet, researchers found, with only 0.001 per cent of the global population being exposed to levels of particulate matter considered safe by the World Health Organization (WHO).

It鈥檚 the first study of its kind to examine air quality on a global scale, according to researchers. Poor air quality can lead to a higher burden of illness in populations, as air pollution can contribute to the risk of strokes and respiratory illnesses.

Most previous studies on air quality have focused solely on city or national levels, or only global trends. This study, published this month in the , looked at daily average concentrations of particulate matter from 2000-2019.

Researchers found that the daily levels of fine particular matter had been decreasing in Europe and North America in the two decades leading up 2019. However, in the same time period, levels increased in Southern Asia, Australia, New Zealand, Latin America and the Caribbean.

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And despite levels decreasing in some regions, more than 70 per cent of the days in the study period had particulate matter concentrations higher than the WHO threshold for safety. Just 0.18 per cent of the global land area had an annual exposure to fine particulate matter below the WHO limit.

鈥淚n this study, we used an innovative machine learning approach to integrate multiple meteorological and geological information to estimate the global surface-level daily (particulate matter) concentrations,鈥� Yuming Guo, professor at Monash University in Australia,

He explained that they examined the concentrations, focusing on areas where the particulate matter levels were above the safe limit designated by WHO. They used a combination of satellite observations and ground-based monitoring.

The study looked specifically at fine particulate matter of 2.5 micrometres or less in diameter, which is considered 鈥渢he most dangerous pollutant鈥� by WHO because its tiny size means it can 鈥減enetrate the lung barrier and enter the blood system, causing cardiovascular and respiratory disease and cancers.鈥�

Air quality is not constant. Due to weather patterns and human activity, air quality in any given region fluctuates, and some regions may have more days with a high concentration of particulate matter than other regions.

One way to measure the air quality is to look at the yearly average concentration of pollutants in the air in a region .

the safe limit for the annual average concentration of this fine particulate matter at 5 micrograms of pollutant per cubic metre, meaning that any region where the annual average concentration is over this figure is considered to have unsafe air quality. It鈥檚 a bar that almost all regions on Earth fail to clear.

But there鈥檚 also safety in terms of exposure on days when the concentration of pollutants in the air is particularly high. The WHO specifies that to stay within safe parameters, a person should not have more than 3-4 days per year where they are exposed to more than 15 micrograms of pollutant per cubic metre for 24 hours. 

Twenty-four hours of exposure to this level of air pollutants for more than four days a year isn鈥檛 safe for the human body, even if a person lives in a region where the annual average air pollution is lower.

The study found that some regions are seeing significantly more days with unsafe concentration levels than others. In eastern and southern Asia, more than 90 per cent of days in the study period had daily particulate matter concentrations above the WHO threshold.

Australia and New Zealand saw air quality worsen in 2019, with a clear increase in the number of days that saw concentrations above the WHO threshold, something researchers theorize could have been connected to increased dust and bushfire events in that year.

In general, Australia, New Zealand and southern America had the lowest annual particulate matter concentrations, the study found.

China had the highest estimated levels of particulate matter concentration in 2000, 2010 and 2019.

While Canada was consistently one of the countries with lower concentration levels and exposed days, we still saw 21.9 days with a concentration above safe levels in 2019, down from 55 days in 2010 and 82.7 days in 2000. Our annual average particulate matter in 2019 was around 16.6 micrograms of pollutant per cubic metre, putting us just above the WHO threshold.

According to the 2019 World Air Quality Report, published in 2020, Canada鈥檚 air is relatively clean compared to other countries, ranked 90th on a list of 98 countries in terms of poor air quality.

Researchers noted that the study can鈥檛 predict personal exposure risks, as its population-weighted exposure estimates assume an equal spread of population across a country geography, something that simply isn鈥檛 the case for the vast majority of regions.

But the hope is that this study will spur a greater understanding of where air quality needs to be addressed across the globe.

鈥淚t provides a deep understanding of the current state of outdoor air pollution and its impacts on human health,鈥� Guo said. 鈥淲ith this information, policymakers, public health officials, and researchers can better assess the short-term and long-term health effects of air pollution and develop air pollution mitigation strategies.鈥�