Urban development in the UAE may have helped to limit pollution levels by reducing the amount of dust whipped up by the wind, according to new research.
The study by scientists at Khalifa University of Science and Technology offered a new perspective on how urbanisation affects air quality by highlighting a way in which it may prove beneficial.
The research also suggested that cloud seeding may likewise have helped to clean the air, by encouraging rainfall.
Scientists found that the aerosol optical depth, which is a measure of the overall quantity of particles in the air, including human-made pollution, has fallen in the UAE in recent decades.
“It was a surprise to see the reversal starting in 2009,” said Dr Diana Francis, one of the study’s authors, who heads Khalifa University’s Environmental and Geophysical Sciences Lab.
“The reduction we found is in the total load of aerosols in the atmosphere, which includes the anthropogenic [human-caused] aerosols.”
The study analysed aerosol optical depth data for the UAE for a 14-year period beginning in 2006.
The reduction that was identified could, the study said, be because rainfall has gradually increased during that period and “changes in land use” have taken place.
“Development in the UAE can generate pollution in the short term (while the construction is going on), but in the long term it contributes to a reduction, especially when we account for the green spaces being developed within the projects,” said Dr Francis.
“All of this reduces the exposed surface to strong winds and reduces the emissions.”
Mineral dust was the most common type of aerosol or suspended particle, and development may cut its release into the air.
The nitty gritty of pollution
Other findings have indicated that pollution levels in heavily urbanised parts of the UAE are high, largely because of traffic emissions, which produce particulate and other pollution, including harmful gases such as nitrogen dioxide.
A 2019 report from Greenpeace listed Dubai as the most heavily polluted city in the region, and the 10th most polluted worldwide.
The new study, which was co-authored by seven of Dr Francis's Khalifa University colleagues, has been published in the journal Earth and Space Science.
The aerosol optical depth data was recorded at two locations in Abu Dhabi emirate, one coastal and the other inland.
Analysis showed that in the warmer months, aerosols tended to be found up to about 4km from the ground surface, whereas in winter, little was present higher than about 2km.
Another recent study of pollution in Dubai and Abu Dhabi, reported in The National, also indicated that high levels of cloud seeding in the UAE may be clearing the air.
However, other researchers, who released their findings early this year, suggested that cloud seeding, in which silver iodide particles are blasted into the atmosphere using aeroplane-mounted flares to encourage water droplet formation, may instead increase ground-level pollution.
The National Centre of Meteorology, which runs the cloud-seeding operations, rejected this suggestion and insisted that the activity cuts pollution.
As well as cloud seeding, the Khalifa University researchers said natural variability could account for growth in rainfall over the period analysed.
While some scientists have highlighted the risks of droughts in the Middle East as a result of climate change, Dr Francis said projections suggested precipitation in the UAE could increase.
“A warmer atmosphere can hold a larger amount of water vapour, but also [there is] a projected expansion of the tropics, which would mean more rain for countries at the latitudes of the UAE,” she said.
“As a result, the aerosol loads are expected to decrease over our region but uncertainty remains, especially related to the impact of increasing temperatures on this process.”
The new study found that aerosol optical depth levels were higher in the spring and summer, partly because south-westerly winds pick up dust during those seasons.
Another finding was that, although aerosol levels as a whole tended to be lower in winter, those generated by pollution were more common in the colder season.