On the Nature of Airborne Aldehydes in a Middle Eastern Megacity: Tehran, Iran

•Formaldehyde (FA) and acetaldehyde (AA) measured in autumn 2018 at a major bus terminal in Tehran.•Mean concentration of FA/AA was 109.99 ± 23.47/85.4 ± 17.17 μg m−3.•The FA:AA ratio was 1.31, with both species linked to vehicles and biogenic emissions.•Statistically significant relationship between FA and AA and the number of buses.•Health risk analysis reveals FA and AA levels exceeded an acceptable limit.