According to a geologist, Beijing's dramatic'sandstorm' was actually something worse.


2013 sandstorm, Beijing. (Feng Li/Staff/Getty Image News)

Due to what was widely reported as a massive sandstorm, Beijing's skies turned orange recently.

The issue, at least in terms of public health, is that there was no sandstorm. There had been a dust storm.

This may appear to be an exercise in geological minutiae, but it represents a significant distinction, and it boils down to a matter of scale. Sand grains are mineral particles with a diameter greater than 0.06 mm, the kind that scratch your ankles on a windy day at the beach and ruin your picnic by making your sandwiches crunchy.

Dust is a much more serious problem than blowing sand.

Dust particles (also known as silt and clay by some geologists) are smaller grains that feel silky to the touch and do not scratch the skin. Importantly, these smaller, lighter grains have the potential to travel much further.

They are not dependent on the sand grains' short-distance ballistic hops, but may become suspended in a global atmospheric process that transports them around the globe. Dust, not sand, can easily travel hundreds of kilometers or even around the world.

The grain size is also important because finer dust particles – those less than 10 micrometers (pm10) and particularly less than 2.5 micrometers (pm2.5) – can be drawn deep into the lungs, posing serious health risks.

Dust storms have existed in China for a long time, long before humans had a significant impact on the landscape. Huge amounts of dust were produced by the advance and retreat of ice sheets during the past 2.6 million years, eventually settling to form loess deposits.

The Chinese Loess Plateau, which covers an area greater than France, has accumulated to a thickness of up to 350 meters over millennia. The loess is nutrient-dense and makes for a productive agricultural soil. It is primarily this farmland that is being eroded and recirculated as dust by the wind.

March 2021 dust storm, showing winds blowing from the Loess Plateau towards Beijing. (NASA)

Is the frequency of dust storms changing now, after such drastic changes in the past? Extrapolating from a single country, such as China, to the rest of the world is not a good idea because the pattern is intricate and there is a lot of variability even within the region.

There is evidence that the frequency of dust storms has decreased in China over the last few decades. Other studies have suggested that dust storms have become more common in some parts of China over the centuries.

The picture is similarly complicated on a global scale. Dust storms have increased in frequency in Israel over the last 30 years, according to studies, while they have decreased in frequency in other areas, according to other research.

Part humans, part nature

So, what is the source of the current dust storms? Is this a purely natural process, a result of climate change, or a result of land mismanagement? The answer is complicated, and it most likely contains some of each of these factors.

A recent study looked at the impact of various dynastic regimes and climate change on the frequency of dust storms in China over the last 2,000 years, and found that an increase in dust storms correlated with both population growth and stronger Asian monsoon circulation.

Surprisingly, increased dust storm activity occurred during periods of increased rainfall, which allowed dynasties to prosper and populations to expand, resulting in increased demand for agricultural land clearance.

The process is mostly natural in other places. Despite its small size, the remote and sparsely populated Bodélé Depression in Chad, in the Sahara, is the world's largest source of atmospheric dust.

This is due to a combination of hyper-arid desert conditions, a highly erodible surface made up of fine relic lake deposits, and nearby mountains that funnel wind across the surface.

On the surface, the story of dust storms appears to be a relentlessly grim picture of landscape erosion, loss of productive agricultural land, atmospheric pollution, and health consequences, but there is a final aspect to the story.

Dust storms are sometimes referred to as "fertilizers" of the oceans' phytoplankton, which is the foundation of most ocean food chains, because of their role in transporting essential mineral nutrients, most especially iron, to the oceans.

According to a 2014 study, wind-blown Saharan dust is responsible for more than three-quarters of dissolved iron in the northern Atlantic, and other studies have indicated that Saharan dust is important in fertilizing the Amazon rainforest with the nutrient phosphorus.

As a result, the story of windblown desert dust, such as that seen over Beijing this week, is complex and global.

Originally Published By The Conversation. Read the Original Article Here.

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