My last office was on Euston Road, a major arterial road through London. On hot days in the Summer I used to feel very wheezy and was constantly coughing as I felt my airways were closing up, to a point where I really should have. This was a combination of hay fever (which has vanished since arriving in HK as my allergy is to grass pollen and there is barely any grass here) and air pollution. Fortunately there are usually only around 10 to 20 hot days a year in London!