Table 5.

Summary of studies examining the association between air quality measures and asthma.

Reference	Data collection period	Location	Study population	Sample size (n or no. studies)	Outcomes	Air quality measures	Findings
Stieb et al. 2008	1981–2000	12 Canadian cities	All ages	NA	Overall mortality	AQHI, SO2, NO2, O3, CO, PM10, PM2.5	Each unit increase in AQHI was associated with an increase of 1.2% in mortality
Stieb et al. 2002	1985–2000	Worldwide	All ages	109 studies	All-cause, respiratory mortality	SO2, NO2, O3, CO, PM10	Acute air pollution exposure was significantly associated with mortality; stronger associations with respiratory mortality for all pollutants except O3
Burnett et al. 1998	1980–1991	11 Canadian cities	All ages	816,991	Mortality of nonaccidental causes	SO2, NO2, O3, CO	All pollutants were significantly associated with mortality; NO2 had the strongest association
Weinmayr et al. 2010	1990–2008	Europe, USA, other	≤ 18 years	36 studies	LRS, cough, PEF of children with asthma	NO2, PM10	PM10 was significantly associated with asthma symptom episode; NO2 was significantly associated with asthma symptoms in overall analysis only considering all possible lags
Stieb et al. 2009	1992–2003	7 Canadian cities	All ages	83,563 (asthma); 125,145 (respiratory)	ED visits for asthma and respiratory infection	SO2, NO2, O3, CO, PM10, PM2.5	Ozone was associated with visits for respiratory conditions; PM2.5 and PM10 were associated with asthma visits in warm season
Lin et al. 2005	1998–2001	Toronto, Canada	≤ 14 years	6,782	Hospitalization for respiratory infection	SO2, NO2, O3, CO, PM10, PM2.5, PM10–2.5	All PM fractions and NO2 were significantly associated with hospital admissions for respiratory infections
Current study 2012	2003–2006	Province of Ontario, Canada	All ages	1.5 million (asthma)	Outpatient, ED visits	AQHI, NO2, O3, PM2.5	AQHI was significantly associated with asthma morbidity on the current day and 1–2 days prior
Abbreviations: LRS, lower respiratory symptoms; NA, not available; PEF, peak expiratory flow; PM10–2.5, PM, with an aerodynamic diameter between 2.5 and 10 µm, coarse PM .