When Christine Li first moved into her flat in Singapore’s northeastern estate of Punggol in 2021, she noticed a strong acrid odour in the air. “Sometimes the smell lingers for weeks and months, it actually made me feel nauseous when we first moved in,” said Li, 42. “At times it smells acidic, and sometimes it smells like something is burning. “We subsequently installed an air conditioner and fan in our living room for ventilation because our windows are always shut to keep the bad air out,” she...