Commuters cover their mouths as they wait to cross a road in the haze in Singapore June 20, 2013. Singapore's air quality deteriorated to "hazardous" levels late on Wednesday as smoke from slash-and-burn land clearing in Indonesia enveloped the city-state, inflaming tensions between the Southeast Asian neighbours. The Pollution Standards Index (PSI) soared to a record high of 321 at 10 pm, up from 290 just an hour earlier and below 200 earlier in the day. A PSI reading above 300 indicates "hazardous" air quality, while a reading between 201 and 300 means "very unhealthy".[Photo/Agencies]