Respiratory hospital admissions and summertime haze air pollution in Toronto, Ontario: consideration of the role of acid aerosols

Environ Res. 1994 May;65(2):271-90. doi: 10.1006/enrs.1994.1037.


A study of air pollution and daily hospital admissions for respiratory causes was conducted in Toronto, Ontario. Fine aerosol (da < 2.5 microns) samples were collected daily at a central city site during July and August 1986, 1987, and 1988 and were subsequently extracted and analyzed for daily particulate phase aerosol strong acidity (H+) and sulfates (SO4 =). Daily counts of respiratory admissions to 22 acute care hospitals and daily meteorological and environmental data (e.g. ozone [O3], total suspended particulate matter [TSP], and thoracic particle mass [PM10] were also obtained. Regression analyses indicated that only the O3, H+, and SO4 = associations with respiratory and asthma admissions remained consistently significant after controlling for temperature. Even after excluding days with maximum 1-hr O3 > 120 ppb, O3 was still strongly significant. In the various model specifications considered, the relative particle metric strengths of association with admissions were generally H+ > SO4 = > FP > PM10 > TSP, indicating that particle size and composition are of central importance in defining the adverse human health effects of particulate matter. On average, summertime haze air pollution was associated with 24% of all respiratory admissions (21% with O3, 3% with H+). On peak pollution days, however, aerosol acidity yielded the highest relative risk estimates (e.g., RR = 1.5 at 391 nmole/m3 H+), and summertime haze was associated with roughly half of all respiratory admissions.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acids / adverse effects*
  • Acids / analysis
  • Aerosols
  • Air Pollution / adverse effects*
  • Air Pollution / analysis
  • Hospitalization / statistics & numerical data*
  • Humans
  • Hydrogen-Ion Concentration
  • Ontario / epidemiology
  • Ozone / adverse effects
  • Ozone / analysis
  • Regression Analysis
  • Respiratory Tract Diseases / epidemiology
  • Respiratory Tract Diseases / etiology*
  • Seasons
  • Sulfates / adverse effects
  • Sulfates / analysis
  • Temperature


  • Acids
  • Aerosols
  • Sulfates
  • Ozone