These days China is almost as well known for its foul skies as for the breakneck economic growth that created the grime. Last week the Beijing city government issued its first “red alert” for smog, shutting schools, halting outdoor construction and ordering temporary closure of some factories. Members of the People’s Armed Police, a paramilitary force deployed to guard foreign embassies and other important sites, were issued with face-masks, also a first. But the public reaction was more grumpy than grateful: no such measures had been taken even the previous week, when concentrations of very small particulate matter—the worst for health—were far higher. Factory activity in neighbouring provinces, typically the prime cause of Beijing’s darkened skies, continued unimpeded. And by declaring an emergency the municipal authorities set a dangerous precedent: claiming authority over a problem they may ultimately be powerless to solve.