Chinese officials argue that the US measure cannot be regarded as accurate because it is based on a reading from a single spot in Beijing.
Even the 203 measure is unremarkable by the capital’s standards. October saw unusually noxious levels of pollution, with many people blaming increased production by factories which knew they would have to shut before Apec. Runners in the Beijing marathon participated in facemasks as the US embassy PM2.5 reading reached 344 micrograms per cubic metre.