Time Magazine: Anyone stepping outside in Beijing around midday on June 18 would have noticed something slightly amiss. The sky was dark enough for cars to use their headlights, and the air was as thick as a smoky bar just before last call. After one of the cleanest springs on record, the Chinese capital’s air quality took an unhealthy plunge for the worse. You wouldn’t have known it by the official numbers. The Ministry of Environmental Protection publishes air quality data online each day at noon, …