Gasping my way through a grey tornado of metal and ash and glass with a handkerchief over my mouth, a bare-torsoed figure emerges from the waters of a fountain by the Holocaust Museum, near Manhattan’s southernmost tip. It is my friend Larry. He has asthma and is wetting his shirt to make it a more effective air filter. We walk home together across the Brooklyn Bridge, with thousands of other silent New Yorkers, as the smoke reaches out for us like a malevolent claw. He wheezes.