For the first time, the hole in the ozone layer has opened up over a populated city, New Zealand scientists say. The hole opened up for two days in early September over the Chilean city of Punta Arenas, exposing its 120,000 residents to very high levels of ultraviolet radiation and increasing their risk of skin cancer. Overall, the ozone hole this year over the Antarctic region was the largest ever, expanding to 11.5 million square miles, or about three times the size of the U.S., according to a separate report released yesterday by NASA’s Goddard Space Flight Center.