Since the end of March, the Beijing Municipal Bureau of Landscape and Forestry has started injecting female poplar and willow plants with an inhibitor to stop them from budding and curb the overabundance of catkin pollen in the air, the Beijing Morning Post reported.

An official with the bureau said the catkin situation usually happens in April and May, and that the trees were mostly planted in the 1960-70s when the choice of landscape trees was limited.

Beijing injected 100,000 trees in 2015 and doubled the number this year. Each injection costs 30 yuan ($4.6) and the drug only works for a year, said the official.