The cities are quickly becoming the most important residential spaces for human beings. According to United Nations, over 55% of global population resided in urban areas as of 2018. This proportion is expected to increase to nearly 68% in 2050.
This unprecedented urban expansion is a catalyst for innovation, economic growth and urban pressure. The World Health Organization has highlighted the severe and multifaceted risks poor air quality presents to human health and socioeconomic activity. Our recent study shows that although NO2, SO2, and CO2 are often blamed for air pollution degradation, atmospheric dust that collects in urban areas is a significant and yet overlooked contributor.
The impact of mineral dust on public health is worthy of more attention
When evaluating the impact of aerosols on air quality, dust from anthropogenic and natural sources is usually viewed as less important. This assumption ignores the growing research that reports airborne dust is a serious health risk and leaves out several key facts.
Dust isn’t a minor component in the aerosol load.
Dust is, by mass, the second most abundant type of aerosol in the world, only surpassed by salt particles. It also makes up the majority of aerosols over continental regions.
Natural sources, mainly in arid or semi-arid regions, are estimated to emit 4,680 Teragrams (1 Tg=1 billion kilograms), of dust each year. This estimate is not enough to account for the total amount of dust in the air.
Around the world, approximately 34 of all dust is caused by natural processes. The remaining 1/4 comes from human activities, which are often concentrated in urban areas and heavily industrialized zones.
These include transportation, development of infrastructure, changes to land use, deforestation and farming practices.
This staggering amount of airborne dust is equivalent to 615,000 Eiffel Towers released into the global atmosphere every year.
Some days, the Eiffel Tower is barely visible. It is Europe’s largest city. Minsky/Shutterstock
The size of the particles that make up these layers is not uniform. The results of large-scale atmospheric pollution experiments (designed to examine pollutants in depth) on mineral dust using airborne instrumentation revealed that the particle sizes in the wind-transported layers of the atmosphere range from less than 0.01 mm, roughly the same size as a SARS CoV-2 virus, to greater than 100 mm, approximately the width of a hair.
The evidence from studies on epidemiology shows that airborne dust can have multiple negative health effects.
Even though coarse mineral dust can cause minor irritations or allergies, even after prolonged exposure, this is not the case with fine particles. These fine particles can penetrate deep into the lungs, causing respiratory, cardiovascular, and allergic diseases. They may even cause cancer. Scientists are also exploring dust’s role as a bacteria carrier, which is suggested by the meningitis epidemics that have occurred in the Sahel Desert.
Fine particles, big questions
This raises a number of questions. To what extent has the airborne fine and coarse dust fractions changed in highly industrialised, densely-populated urban areas over the last two decades?
Are there any trends that are increasing or decreasing in the changes we observe?
What major cities are experiencing, or will experience in the future, air pollution levels that exceed WHO safety standards?
Satellite observations of megacities over 15 years reveal dust changes
Our recent study examined Earth observation data from satellites spanning 15 years to gain a greater understanding of the amount of dust that urban populations actually breathe in. Our study examined the temporal dynamics and accumulation of dust at the bottom of the atmosphere above Earth’s surface, in 81 cities with populations greater than 5 million. This is where the most human activity occurs. There are several key takeaways from the results:
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In a large number of urban centers around the world, atmospheric dust is a health hazard. According to UN data, approximately nine out of ten of the 800 million residents of the world’s 81 biggest cities live in areas where dust concentrations exceed the annual average air quality thresholds. The most heavily affected areas are located in urban centers of the Middle East and Indian subcontinent. They also include East Asia, Sahel, and East Asia.
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In most major cities, dust levels are declining.
This encouraging news is not without two caveats. In many cases the declining trend in dust levels over time may not be statistically significant, and the total amount of dust still remains high.
Even where there are reductions, this may not be a meaningful improvement in the health risks.
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The challenge will not disappear in the future. UN estimates show that urban population in megacities will grow to more than one billion by mid-30s.
As a result, dust in the atmosphere will continue to be a health risk, but to a lesser degree, due to a perceived decline of atmospheric loads compared with current conditions. However, it could affect a greater number of people.
Airborne dust: From science to policy
As scientific evidence grows that dust in the air is a health risk, many countries have strengthened their air quality laws and launched national and international initiatives aimed at tackling dust problems.
The World Meteorological Organization, DANA, CAMS NCP, among other initiatives, are a reflection of the growing collaborative efforts to improve the monitoring, the modelling and the translation from science into real-world solutions. At the same, government regulations are being aligned with WHO recommendations.
The revised Ambient Air Quality Directive of the European Union, for example, explicitly recognizes that natural aerosols such as dust are cumulative hazards to health.
Together, research advancement, policy coordination, and better regulation create a solid foundation for taking action.
Urbanisation is accelerating, so tackling air pollution, such as atmospheric dust, becomes more important to protect public health and ensure a sustainable future in the rapidly expanding cities of the world.
The Axa Research Fund, now a part of Axa Foundation for Human Progress, was created in 2007 with the goal to accelerate scientific research on important societal risks. It has funded over 750 project around the globe. Visit the AXA Research Fund website or @ AXAResearchFund LinkedIn to learn more..
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