A day before the Communist Party of China gathered in Beijing on July 1 to mark one hundred years of its rule, Chinese authorities launched a large-scale operation to seed clouds, and ensure rainfall over Beijing. The result: Air pollutants cut by two-thirds, improving the air quality from “moderate” to “good”. A relatively pollution-free summit ensued.
The cloud seeding operation was studied by researchers from Tsinghua University, China’s most prestigious public institute, the South China Morning Post reported. A research paper published in Environment Science estimated that the artificial rain created that day reduced PM2.5 air pollutant levels by two-thirds, noting that the drop in pollution was unlikely to have a natural cause since the artificial rain was the only disruptive event in that period.
The centenary event on July 1 saw tens of thousands participate in a ceremony in Tienanmen Square. Controlling air pollution in Beijing is often a concern for authorities ahead of major events. So, the day before, a two-hour cloud seeding operation was launched, using rockets bearing silver iodine. The South China Morning Post spoke to residents who heard the rockets being launched.
The process causes water droplets to cluster with silver iodide par and increase the chance of precipitation. The CPC ceremony took place amid overcast conditions and it rained just after it ended, SCMP reported.
The event presented unique challenges, the paper noted. While industrial activity had been halted in Beijing and nearby provinces, air circulation had also slowed making it harder for pollutants to dissipate.
China has invested in cloud-seeding technology for some time now. In 2020, it launched a weather modification programme covering much of its western regions including Xinjiang and Tibet. In Tibet, China plans the world’s largest cloud-seeding operation, one that uses burners to loft silver iodide particles into the atmosphere.
Criticism of cloud-seeding technologies includes the risk that it could trigger unknown consequences.