Long-term exposure to particulate matter (PM) 2.5 -- a mixture of solid particles and liquid droplets found in the air -- doubles the risk of losing smell, a hallmark of Covid-19, according to a study.The loss of smell, a condition known as anosmia, can severely impact a person's quality of life, making it extremely difficult to taste foods, detect airborne hazards in the environment, and carry out other functions dependent on the senses.Covid-19 has further thrust olfaction into the spotlight as olfactory disturbances appear to be both a cardinal symptom and, in some cases, a debilitating consequence of the ongoing global pandemic, said researchers from the Johns Hopkins University in the US.While previous research has associated PM2.5 as a likely culprit for anosmia, the team from Johns Hopkins conducted a new study to better understand how long-term exposure to air pollution can rob someone of the ability to smell and taste.They found long-term airborne exposure to PM2.5 increases the risk of losing one's smell by nearly twice (a 1.6- to 1.7-fold increase).This may occur because the location of the olfactory nerve, which contains the sensory nerve fibres relating to the sense of smell, places it directly in the path of inhaled PM2.5 materials. The findings appeared in the JAMA Network Open."Based on this result, we feel that long-term exposure to high levels of PM2.5 represents a common risk factor for the loss of sense of smell, especially in vulnerable populations such as older people -- but also one that is potentially modifiable if sources of PM2.5 components can be better controlled," said lead author Murugappan Ramanathan, rhinologist and associate professor of otolaryngology -- head and neck surgery at the University's School of Medicine.In their study, the researchers looked at 2,690 people, aged 18 and older, who were evaluated by otolaryngologists between January 2013 and December 2016. Of these, 538 were diagnosed with anosmia, with an average age of 54 and with men making up the majority (339 or 63 per cent).Exposure to PM2.5 has been already linked to cardiovascular disease, lung cancer, decline in cognitive thinking ability, chronic obstructive pulmonary disease, asthma and premature death.