The air pollution in Mexico City is so bad that it could be harming residents’ sense of smell, researchers say. People who live in the city, which exceeds the World Health Organization’s ozone standards 300 days out of the year, did a worse job identifying common scents like coffee and orange juice than residents of a neighboring rural area. They also took longer to detect the smell of rotten food. Why the nose damage? “The olfactory receptors are very exposed [to pollutants],” says researcher Robyn Hudson. “They are just hanging out there in the mucus.” To use the scientific terms.