Individuals predisposedwith inflammatory disorders, such as asthma,7 chronic obstructive pulmonary disease (COPD),8 or cystic fibrosis,9 are especiallysusceptible to air pollution, but the underlyingmolecular mechanisms have been unclear.10,11 Elevated nitricoxide (•NO) concentrations from inducible nitricoxide synthase (iNOS) in the lungs have been observed in individualswith these inflammatory disorders.12−15 Exhaled •NO(eNO) can reach volume mixing ratios up to several tens of ppb inthe breath, exceeding typical ambient •NO concentrations.16−18. Here, NOS2 is linked to asthma.