Why did 'particle pollution' increase in UAE as roads emptied during pandemic?

When governments introduced stay-home measures in early 2020 in response to the coronavirus pandemic, air pollution fell, in general, thanks to reduced traffic and the closure of industrial plants.

The UAE itself enjoyed a significant drop in nitrogen dioxide levels between February and April of that year, figures published by the Ministry of Climate Change and Environment showed, due to the scaled-down activities.

However, a new study by scientists in the Emirates has found that, against expectations, concentrations of tiny particulate matter in the air in eastern Arabia, including the UAE, increased during this time.

The reason for this was an unusually active period of dust storms, which was caused by the region’s Shamal winds.

“While the reduction in the concentration of pollutants such as sulphur dioxide, nitrogen dioxide and carbon monoxide has been widely reported, in the vast majority of the published studies the particulate matter concentration also decreased,” the study said.

“Over the eastern Arabian Peninsula, however, it actually increased due to a more active wind flow.”

The study reports that from March to June 2020, the level of particulate matter (PM) in eastern Arabia was 30 per cent higher than the average seen from 2016 to 2019.

Scientists looked at both PM10 — particulate matter up to 10 micrometres in diameter — and PM2.5 — up to 2.5 micrometres in diameter- and found that some measurements were up 45 per cent.

In stark contrast, concentrations of nitrogen dioxide, sulphur dioxide and carbon monoxide — all pollutants released by vehicles — dropped up to 40 per cent in the UAE over the same period.

Findings a 'surprise' to experts

The increases in particulate matter were “indeed a surprising finding”, said the study’s first author, Dr Diana Francis, who heads the Environmental and Geophysical Sciences (Engeos) Laboratory at Khalifa University in Abu Dhabi.

“We expected cleaner air with less pollutants due to the reduction in human activity and the transport sector. But the data showed an increase in particulate matter,” she said.

“The harmful chemical pollutants, such ozone and nitrogen oxides, decreased, and this was observed from both ground and space. It is the particulate matter that did not follow this trend.”

Particulate matter can cause health effects including everything from sneezing and a runny nose to heart disease and lung cancer.

A rise in the Shamal winds in the region caused the rise in dust storms, which Dr Francis described as “persistent and sustained over several days”.

In an additional twist, air quality improvements in India due to lockdowns may have helped cause the heavy winds and rises in particulate matter in the UAE and surrounding areas.

The Shamal winds were the result of an air pressure gradient created by high pressure over North Africa and low pressure over the Indian subcontinent.

“In 2020, the low-pressure system over the Indian subcontinent was deeper due to lockdown measures over there and a reduction in pollution, which allowed for more solar radiation to reach the ground and warm the surface,” Dr Francis said.

It is not only wind conditions that determines whether dust storms will form; it is also due to the soil being suitably dry.

“In some years, the wind conditions are satisfied to have dust storms but the soil conditions are not met or vice versa,” said Dr Francis.

“That’s why it is still difficult to predict their future trends, even using very sophisticated tools such as the climate models.”

Typically, there is more erodible material on the surface in the spring, when the soil is dry and there is likely to have been rainfall, which makes dust storms more likely.

The study was written by Dr Francis, two colleagues at Khalifa University and three researchers at the Environment Agency Abu Dhabi and is being published in the journal Aeolian Research.

“Aeolian” means “related to wind” and is inspired by Aeolus, the keeper of the winds in Greek mythology.