Participants will be invited to take part by either Dr James Scales or by a primary care practitioner in their General Practice clinics. Participants will provide informed consent after they have read the study information sheets and have time consider their involvement (minimum 24 hours) and ask any questions.

Upon providing informed consent the participants will visit QMUL laboratories for a screening assessment. During this one hour visit they will complete a submaximal exercise test on a static bike (to provide estimates of maximal exercise capacity to standardise exercise exposure protocol) and perform pre and post bronchodilator spirometry and exhaled nitric oxide testing and oscillometry. At this point participants will be sent an online link to the symptom surveys. Surveys will be explained to the participants and they will be asked to complete the surveys they days before the testing visits. Participants will be provided with personal air quality monitor, heart rate monitor and physical activity monitor to wear three days before the exposure visit.

Participants will be invited to visit one of three field based study sites in a random order. Study sites will be located in walled gazebos next to air quality monitoring sites (managed by our collaborators at ICL) positioned near roads to provide the required air quality exposure. The protocol for the three visits will be identical and each visit will be separated by at least two weeks (washout). Participants will initially provide a urine sample at home and will bring the sample with them to the testing site. To control for participant exposures before testing, a taxi will be provided for the participant. Participants will travel with car windows closed, and air recirculation turned on. Participants will arrive that the study site at 10:00am, and will be joined by up to three other participants. In the first hour the participants will perform the respiratory health assessments and will provide a blood and a nasal mucus sample. After performing all the pre exercise tests participants will wear a heart rate monitor and will commence the exercise protocol (six exercise bouts of 15 minutes separated by fifteen-minute rest periods on a static exercise bike). Half-way through the protocol participants will perform spirometry, impulse oscillometry and FeNO testing. Upon completing the two-hour exercise protocol participants will complete the same battery of health assessments and will provide nasal mucus samples. Participants will leave the assessment area at about 14:00pm. Air pollution measurements will be taken for the duration of the time that the participant visits the exercise location.

24 hours after the exercise protocol participants will visit the QMUL laboratories to perform the health assessment tests again and to provide a mucus sample via nasal lavage, blood sample via venepuncture and provide a urine sample. After repeating this process three times (one visit to each field site) they will receive an expenses payment of £200 and leave the study. Participants will be paid £60 per exposure visit and £20 pre-screening visit. Participants will be paid for each visit they attend and will be paid when they complete participation or withdraw from the study.