Source: The Conversation – France – By Emmanouil Proestakis, National Observatory of Athens
Cities are rapidly becoming the defining residential space of human life. Over 55% of the global population lived in urban areas in 2018, a proportion projected to reach nearly 68% by 2050, according to the United Nations (UN).
While this unprecedented urban growth fuels innovation and economic activity, it simultaneously concentrates human exposure to environmental stressors and intensifies urban environmental pressures. In this context, the World Health Organization (WHO) has underlined the multifaceted challenges and severe risks that poor air quality poses to socioeconomic activities and human health. And although emissions – such as NO₂, SO₂, CO₂ and O₃ – are the usual suspects when it comes to air quality degradation, our recent study highlights that atmospheric dust that accumulates over urban areas represents an additional and considerable, yet frequently overlooked, contributor to adverse health implications.
Mineral dust’s impact on Public health deserves more attention
Among the aerosol species contributing to air quality degradation, atmospheric dust originating from natural sources and anthropogenic activities is often considered less consequential. However, this assumption overlooks a growing body of research evidence reporting on airborne dust as a health hazard and neglects several important facts.
To begin with, dust is not a marginal component of the total aerosol load. By mass, dust is the second-most abundant aerosol type globally, surpassed only by sea-salt particles, and the dominant component of the atmospheric aerosol load over large continental areas.
More specifically, it has been estimated that natural sources – mainly arid and semi-arid areas – emit around 4,680 teragrams (Tg) (1 Tg= 1 billion kilograms) of dust into the atmosphere each year. Yet, this estimate does not account for all the dust present in the atmosphere.
Globally, natural processes contribute to approximately three quarters of the total dust load, with the remaining quarter linked to human activities frequently evolving around urban and highly industrialised areas, including transportation, infrastructure development, land-use change, deforestation, grazing and agricultural practices.
To put this into perspective, this staggering airborne dust mass exceeds 615,000 times the equivalent weight of the Eiffel tower released globally into the atmosphere each year.
Furthermore, these particles composing the atmospheric dust layers are far from uniform in size. Large-scale experiments, (designed to study atmospheric pollutants in detail) focusing on mineral dust and employing airborne in situ instrumentation have revealed that particles in wind-transported atmospheric layers range widely in size, from less than 0.1 μm (roughly the size of a SARS-CoV-2 virus (coronavirus) to more than 100 μm (approximately the diameter of a human hair).
More concerning is that accumulated evidence from epidemiological studies links airborne dust to multiple adverse health outcomes. While coarse mineral dust is often considered relatively harmless, typically causing minor skin irritation or allergic reactions even over long exposure periods, it is a completely different story when it comes to fine particles. Because of their small size, these fine particles allow for deep lung penetration that potentially triggers respiratory and cardiovascular diseases, allergic reactions, even cancer. Beyond these direct effects, scientists are still exploring the role of dust as a carrier for bacteria, as suggested by meningitis outbreaks in the Sahel desert.
Fine particles, big questions
These concerns naturally raise a series of questions: to what extent have the fine-mode and coarse-mode fractions of airborne dust changed over highly industrialised and densely populated urban areas in the past two decades?
Can we detect meaningful, increasing or decreasing temporal trends in these changes? Which major cities currently experience, or are likely to experience in the near future, dust concentrations exceeding WHO air quality safety thresholds?
Megacities under the microscope: 15 years of satellite observations reveal how dust levels are changing
To gain a better understanding of how much dust urban populations are actually breathing in, our recent study examined satellite-based Earth observations spanning over 15 years. We examined the accumulation and temporal dynamics of dust in the lowest atmospheric layer above the Earth’s surface in 81 of the world’s largest cities and urban areas (with populations exceeding 5 million), where human activity and exposure are most prevalent.
The results reveal several important takeaways:
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Atmospheric dust unequivocally poses a hazard to public health in a substantial number of major urban areas worldwide. Based on population data and projections provided by the UN approximately 9 out of 10 of the roughly 800 million people living in the 81 largest cities are exposed to dust levels exceeding annual-mean air quality safety thresholds. A clear geographic pattern emerges, with the most affected urban areas located in the Middle East, the Indian subcontinent, East Asia, and the Sahel.
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Dust levels appear to be declining in most large cities. However, this encouraging, seemingly positive news comes with two important caveats: in many cases, the temporal declining trends are not statistically significant and frequently the overall dust burdens remain considerable. In other words, even where reductions are observed, they may not translate into meaningful reductions in health risk.
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Looking ahead to the near future, the challenge is unlikely to disappear. According to estimates provided by UN, urban populations in these megacities are projected to grow, reaching more than 1 billion people in the mid-thirties.
Consequently, atmospheric dust will remain an environmental health hazard, however, of a lower degree due to the apparent declining atmospheric load compared to present-day conditions, yet potentially affecting a larger number of individuals.
From science to policy: tackling the hazard of airborne dust
In response to mounting scientific evidence that airborne dust poses a risk to human health, countries are strengthening air quality legislation and launching national and international initiatives to confront dust-related challenges.
Efforts such as the World Meteorological Organization’s SDS-WAS, DANA and CAMS NCP among others, reflect growing collaboration to improve monitoring, modelling, and the translation of science into practical solutions. At the same time, governments are moving to align regulations with WHO recommendations.
For instance, the European Union’s revised Ambient Air Quality Directive explicitly recognises natural aerosols like dust as a cumulative health hazard. Together, advancing research, coordinated policy, and improved regulation provide a stronger foundation for action.
As urbanisation accelerates, tackling air quality, including atmospheric dust, is becoming central to protecting public health, strengthening urban resilience, and ensuring a more sustainable future for the world’s rapidly growing cities.
Created in 2007 to help accelerate and share scientific knowledge on key societal issues, the Axa Research Fund – now part of the Axa Foundation for Human Progress – has supported over 750 projects around the world on key environmental, health & socioeconomic risks. To learn more, visit the website of the AXA Research Fund or follow @ AXAResearchFund on LinkedIn.
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Emmanouil Proestakis has been supported by the AXA Research Fund for postdoctoral researchers under the project entitled “Earth Observation for Air-Quality – Dust Fine-Mode (EO4AQ-DustFM).
– ref. Atmospheric dust: the overlooked suspect in urban air pollution – https://theconversation.com/atmospheric-dust-the-overlooked-suspect-in-urban-air-pollution-276422
