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Chinese weather authorities successfully controlled the weather ahead of a major political celebration earlier this year, according to a Beijing university study. The Guardian reports: On 1 July the Chinese Communist party marked its centenary with major celebrations including tens of thousands of people at a ceremony in Tiananmen Square, and a research paper from Tsinghua University has said an extensive cloud-seeding operation in the hours prior ensured clear skies and low air pollution. [...] On Monday the South China Morning Post reported a recent research paper which found definitive signs that a cloud-seeding operation on the eve of the centenary had produced a marked drop in air pollution. The centenary celebration faced what the paper reportedly termed unprecedented challenges, including an unexpected increase in air pollutants and an overcast sky during one of the wettest summers on record. Factories and other polluting activities had been halted in the days ahead of the event but low airflow meant the pollution hadn't dissipated, it said. The paper, published in the peer-reviewed Environmental Science journal and led by environmental science professor, Wang Can, said a two-hour cloud-seeding operation was launched on the eve of the ceremony, and residents in nearby mountain regions reported seeing rockets shot into the sky on 30 June. The paper said the rockets were carrying silver iodine into the sky to stimulate rainfall. The researchers said the resulting artificial rain reduced the level of PM2.5 air pollutants by more than two-thirds, and shifted the air quality index reading, based on World Health Organization standards, from "moderate" to "good." The team said the artificial rain "was the only disruptive event in this period," so it was unlikely the drop in pollution had a natural cause.