By Thomas Baird
Tell anyone at a party that you study dust and they’ll automatically think of neglected corners of their house. Tell anyone that it’s dangerous mineral dust in the atmosphere and you’ll get a laugh, a pitiful look, and then be uninvited from the next event. But dust in the atmosphere affects more than just your pristine skirting boards. Indeed, it is a startlingly hazardous substance which is often overlooked in everyday life. From their source, dust particles can travel huge distances, exacerbate air pollution, and even impact the health of cities. So, no matter how many party invites you might lose out on, there are some key aspects of dust that you should be aware of.
Dust gets everywhere
You don’t need to be a homeowner to know that dust can get just about everywhere. The same is true for dust in the atmosphere (it’s called entrained dust). Although the majority of dust storms last between 2 to 6 hours and are relatively localised, they have the potential to be extremely well travelled. In some rare occasions, atmospheric dust has been observed completing a full circuit of the globe in just 13 days.
But if you’re thinking “I’m not anywhere near a dust source!”, you’re not out of the proverbial woods just yet. NASA has calculated that 182 million tons of dust is transported out of the Sahara – that’s about 675,000 full lorries worth. Despite losing a few of these loads into the ocean, it is estimated that over a hundred thousand of these truck-loads land across South America alone. That’s a distance of almost 10,000 km! Even after this monumental migration, dust particles still pack a punch, providing vital nutrients to the Amazon and helping to create one of the most productive ecosystems on Earth.
What do you call a dust storm?
Not to be pedantic, but there’s no such thing as a sandstorm. Sand is much too large and heavy to be suspended in the atmosphere for long periods of time. Even with a fast wind, sand won’t go much higher than your ankle. Rather, the technical name for a dust storm is a haboob.
Haboobs are clouds of silt-sized particles (0.004-0.06 mm) that cannot be seen with the naked eye. Produced as a result of weathering, volcanic eruptions, or manufacturing, these particles are small enough to be easily entrained into the atmosphere by gusts of wind. Lacking in vegetation to anchor the topsoil, the majority of haboobs are sourced from deserts and arid regions.
Haboobs can give rise to “Blood rain”, a rather biblical event that you have most definitely been subjected to at least once in your lifetime. The horrific, but not quite accurate, title refers to when atmospheric dust mixes with rain clouds producing rust. In April 2016, Italy, France, and much of Eastern Europe woke up to cars coated in a rust-coloured patina. Sourced from the Sahara, the dust had been carried in the atmosphere and deposited across Europe by a rainstorm. These deposits were thick enough to trigger health warnings in London.
Dust can kill
Due to their small size, dust particles can be inhaled and enter the respiratory tracts of people and animals. During Blood Rain events, health officials note that people with heart and lung conditions will see their symptoms exacerbated, and advise asthma sufferers to reduce outdoor physical exertion.
Dust can be particularly problematic for urban environments, where air quality is already a major health issue. In September 2016, the World Health Organisation (WHO) released a report on exposure to atmospheric pollution which estimated that 92% of the world’s population live in areas where air quality exceeds recommended levels, with many of the worst polluted cities located near areas of dust production.
Dust isn’t just a respiratory hazard; it can also be a vector for disease. For instance, the influenza virus has been found in samples of atmospheric dust over Taiwan1. Similarly, the bacteria, Clostridium perfringens, the third most common cause of food poisoning in the UK and US, has been found in dust over Kuwait and Iraq. Even fungal communities and pollen spores have been found in samples of dust!2
You can’t run, you can’t hide
As we don’t seem to be able to outrun the impacts of dust storms, it’s important to understand whether they are increasing in frequency. The eminent desert geomorphologist Andrew Goudie’s 2014 review attempts to address this question.
The answer, however, is somewhat nuanced. The current literature paints a picture of a shifting global patchwork, with dust storms increasing in frequency in some areas and decreasing in others.
This lack of clarity is especially concerning as dust storms also have indirect impacts on human life. The Science of The Total Environment journal recently published an investigation into the impact of dust on global atmospheric patterns3. Dust storms are known to act as cloud nuclei, allowing water droplets in the air to adhere to their surface creating clouds. By acting as cloud nuclei, dust aerosols have the potential to intensify hurricane events, change the amount of solar energy that is reflected by the Earth’s atmosphere, and influence rainfall patterns. Although our understanding of these areas requires further study, as climate change begins to take hold, these areas are ones to look out for.
So, the next time you attend a party, make sure all your fellow party-goers know the importance of dust emissions and their hazards. From fertilizing the Amazon to increasing mortality rates across a city, dust storms have the potential to be a very powerful phenomenon. Something I think you’ll remember the next time you wake up to a rust-coloured car.
In discussions with your hosts, sprinkle in mentions of haboobs and blood rain. But, in order to get an invite again next time, never call them sandstorms.
1. Chen, Tsai, Lin et al (2010) Ambient Influenza and Avian Influenza Virus during Dust Storm Days and Background Days. Environ Health Perspect 118:1211-1216. Doi: 10.1289/ehp.0901782
2. Goudie (2014) Desert dust and human health disorders. Environment International 63: 101-113. Doi: 10.1016/j.envint.2013.10.011
3. Zheng, Zhao, Che et al (2016) A 20-year simulated climatology of global dust aerosol deposition. Science of The Total Environment 557–558: 861-868. Doi: 10.1016/j.scitotenv.2016.03.086