Those previously unseen numbers were hard to believe, but they did seem tomatch up well enough with the noxious soup we could see, smell and tasteoutside. We are all far more familiar with the specifics of air-qualitymeasurement than we would like to be. Apart from the AQI readings above 700, wewere quite struck to see the readings for the smallest and most dangerous sortof particulate matter, called PM 2.5, which can enter deep into the respiratorysystem. These are named for the size, in microns, of the particles. A reading ata controversial monitoring station run by the American embassy showed a PM 2.5level of 886 micrograms per cubic metre; Beijing’s own municipal monitoringcentre acknowledged readings in excess of 700 micrograms.
For perspective on that set of figures, consider that the guideline valuesset by the World Health Organisation regard any air with more than 25 microgramsof PM 2.5 per cubic metre as being of unacceptable quality.
Chinese authorities have complained about the American embassy's insistenceon independently monitoring—and publicly reporting—Beijing’s air quality. Andsometimes much is made of the vast differences between those readings andChina’s own official ones, which are often less dire. Indeed, a key feature ofone of those mobile-phone apps is the side-by-side comparison of those competingdata-sets. (It is of course a bad sign that people here need more than one appto keep up with all this.)
But on a day like Saturday, the discrepancy between official readings andindependent ones hardly seemed to matter; you didn't need a weatherman to knowwhich way the ill wind blew. Or failed to blow, as the case may have been. Oneexpert quoted by Chinese media attributed this spike in pollution to a series ofwindless days that allowed pollutants to accumulate.