Sydney overkill and Beijing underkill

Earlier this week, various blogs and media outlets reported that Beijing was experiencing frightful levels of air pollution. To document the crisis, China hand James Fallows cited what he called "the indispensable (and highly controversial)" Twitter feed @Beijingair, which produces hourly readings of  fine particulate matter (PM2.5) in Beijing. On Monday, @Beijingair showed readings in excess of 300 µg/m3, contributing to conditions the US EPA characterizes as "hazardous," and warranting "health warnings of emergency conditions." What caught my attention was Fallows's assertion that the @BeijingAir feed is "the only known source of PM 2.5 readings in China." That is astounding: one PM2.5...