Could a past cold make your lungs more sensitive to air pollution?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Individuals between 18-55 yrs. of age (No subject will be excluded from the study on the basis of gender or ethnicity) * Individuals with knowledge of prior respiratory viral infection history allowing them to be segregated into one of three cohorts * Cohort 1 - No history of respiratory viral infection (defined as no symptoms consistent with respiratory viral infection nor history of a positive respiratory viral test) * Cohort 2 - Documented mild respiratory viral infection (a positive test, either PCR- or antigen-based) but with mild to no symptoms and no evidence of a lower respiratory tract infection (including no hospitalization, and no oxygen use) * Cohort 3 - History of respiratory viral infection and symptoms/imaging consistent with a lower respiratory tract infection who have recovered, are \>6 months out from their infection, and have normal lung function (spirometry with FVC, FEV1 and FEV1/FVC) * There will be no maximal period from respiratory viral infection for inclusion in the study, the minimal period will be \>6 months out from infection Exclusion Criteria: * Individuals with prior respiratory viral pneumonia who have ongoing respiratory symptoms, are still using supplemental oxygen, or have abnormal lung function * Current smokers of tobacco products including e-cigarettes or those with previous smoking history within the prior 5 years * Pregnant women and women who are presently lactating. * Subjects that have received antibiotic administration or an upper respiratory infection within the previous 4 weeks * College and graduate students or employees who are under direct supervision by any of the investigators in this protocol * Alcohol or illicit substance abuse * Chronic cardio/pulmonary respiratory disorders or other medical conditions as determined by the investigator * Increased airway hyperresponsiveness at baseline as measured by a positive methacholine challenge response (methacholine PC20 FEV1 \< 4 mg/ml) * Subjects will be requested to refrain from antihistamines, nonsteroidal anti-inflammatory agents, antioxidants (e.g. beta-carotene, selenium, and lutein) and supplemental vitamins (e.g. C and E), for 1 week prior to, and during testing.