The organisation behind the UAE's cloud-seeding operations rejected the findings of a recent study that concluded the work increased pollution levels.
The research suggested that blasting tiny particles into the air as “condensation nuclei” around which water droplets form caused a seasonal surge in particulate matter (PM) pollution.
But the National Centre of Meteorology (NCM) said that salt particles fired into the atmosphere by aircraft would not increase pollution at ground level.
Based on data from 20 Environment Agency Abu Dhabi pollution monitoring stations, the research analysed data for the early months of 2017.
From January to March that year, the NCM undertook about 70 cloud-seeding missions, according to the study, which was published last month in the International Journal of Environmental Science and Technology.
Aircraft equipped with flares send silver iodide particles into the atmosphere to encourage the formation of water droplets, which leads to rain.
The researchers looked at data on PM10, which is particulate matter up to 10 micrometres in size, and PM2.5, or particles with a diameter up to 2.5 micrometres.
“Data from all stations showed a significant increase in PM10 concentrations during January-March 2017, when the cloud mission occurred, compared to the months thereafter,” wrote the researchers, Dr Ashraf Farahat, of King Fahd University of Petroleum and Minerals in Saudi Arabia, and Dr Abdelgadir Abuelgasim of UAE University in Al Ain.
“This result indicated that the silver iodide crystals [that were] fired into the clouds but failed to take part in any nucleation process eventually fell down while degrading into smaller particles, forming PMs of different sizes that may be suspended and float in the atmosphere.”
While the researchers concluded that cloud seeding increased PM10 levels, they did not find the same effect with PM2.5.
Particulate matter is linked to harmful health effects, including asthma attacks, lung cancer and heart disease.
As reported in The National in January, scientists at American University of Sharjah suggested that it improved the UAE's air quality, because the rainfall cleared away dust and other suspended particles.
Dr Farahat and Dr Abuelgasim acknowledged that cloud seeding could improve air quality and visibility “where rain washes out some of the dust and suspended particles in the atmosphere”.
"However, among researchers, there are still debates and contrasting opinions on whether cloud seeding is an effective technique in producing a significant increase in rain," they said.
The UAE's cloud-seeding operation is an active one, with the NCM conducting a reported 200 missions in the first six months of last year.
They are carried out because the UAE has low precipitation levels, with most areas typically receiving less than 100mm a year.
The authorities want more rain to protect the country’s highly stretched water resources, with extraction for domestic use, agriculture and industry depleting reserves in underground aquifers.
In response, an NCM official who works on cloud seeding told The National that it "is not a scientific view" to suggest that cloud seeding, which has been carried out in the UAE for two decades, increased pollution. Instead, he said, it "improves air quality".
“The piece is talking about how the cloud seeding can increase PM10 and PM2.5. There’s no relation at all,” he said.
He said there were salts "available in huge amounts in the atmosphere" naturally and that cloud seeding had a localised effect high up, with the flares that released the particles being fired at an altitude of about 2,400 metres.
“We are making them concentrated in a small part of the cloud. After that they’re distributed by the wind,” he said.
“This is very different to deposits on the surface. The measurements [in the new study] have been taken at surface level.”
As reported in The National this week, the NCM is looking for new ways to encourage rain and, with UK researchers, will test drones that deliver an electric charge to air molecules.
The hope is that this will encourage rain by causing water droplets to merge.