Inclusion Criteria:  Adults, over the age of 18 and able to give informed consent Symptom free from any respiratory illness in the last 48 hours  Exclusion Criteria:  Pregnant (where the participant feels that their pregnancy will make participation uncomfortable) Inability to give consent Current respiratory disease. Participants with well controlled asthma will be included (defined as asthma that the participant self-rates their asthma as being under control and that does not limit exercise, work)