PM	particulate matter
PM2.5	fine particulate matter ≤ 2.5 µm in aerodynamic diameter
PM10–2.5	coarse particulate matter between 2.5 and 10 µm in aerodynamic diameter
O3	ozone
FEV1.0	forced expiratory volume in one second
FVC	forced vital capacity
MMEF	maximal mid-expiratory flow
PEF	peak expiratory flow rate
$\stackrel{·}{\mathrm{V}}$50/$\stackrel{·}{\mathrm{V}}$25	The ratio of the maximum expiratory flow rate at 50% of the FVC to the maximum expiratory flow rate at 25% of the FVC
FeNO	fractional exhaled nitric oxide
I/O ratio	indoor-to-outdoor concentration ratio
SD	standard deviation
BMI	body mass index
CI	confidence interval