title: Synoptic weather typing applied to air pollution mortality among the elderly in 10 Canadian cities.
abstract: BACKGROUND
  Synoptic circulation patterns (large-scale weather systems) affect ambient levels of air pollution, as well as the relationship between air pollution and human health.
  
  
  OBJECTIVE
  To investigate the air pollution-mortality relationship within weather types and seasons, and to determine which combination of atmospheric conditions may pose increased health threats in the elderly age categories.
  
  
  METHODS
  The relative risk of mortality (RR) due to air pollution was examined using Poisson generalized linear models (GLMs) within specific weather types. Analysis was completed by weather type and age group (all ages, ≤64, 65-74, 75-84, ≥85 years) in ten Canadian cities from 1981 to 1999.
  
  
  RESULTS
  There was significant modification of RR by weather type and age. When examining the entire population, weather type was shown to have the greatest modifying effect on the risk of dying due to ozone (O3). This effect was highest on average for the dry tropical (DT) weather type, with the all-age RR of mortality at a population weighted mean (PWM) found to be 1.055 (95% CI 1.026-1.085). All-weather type risk estimates increased with age due to exposure to carbon monoxide (CO), nitrogen dioxide (NO2), and sulphur dioxide (SO2). On average, RR increased by 2.6, 3.8 and 1.5% for the respective pollutants between the ≤64 and ≥85 age categories. Conversely, mean ozone estimates remained relatively consistent with age. Elevated levels of air pollution were found to be detrimental to the health of elderly individuals for all weather types. However, the entire population was negatively effected by air pollution on the hot dry (DT) and hot humid (MT) days.
  
  
  CONCLUSIONS
  We identified a significant modification of RR for mortality due to air pollution by age, which is enhanced under specific weather types. Efforts should be targeted at minimizing pollutant exposure to the elderly and/or all age groups with respect to weather type in question.
authors.affiliation: Health Canada, Environmental Health Science and Research Bureau, Population Studies Division, 50 Colombine Driveway, Ottawa, ON, Canada K1A 0K9.
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Vanos
authors.forename: Sabit
authors.initials: S
authors.lastname: Cakmak
authors.forename: Corben
authors.initials: C
authors.lastname: Bristow
authors.forename: Vladislav
authors.initials: V
authors.lastname: Brion
authors.forename: Neil
authors.initials: N
authors.lastname: Tremblay
authors.forename: Sara L
authors.initials: SL
authors.lastname: Martin
authors.forename: Scott S
authors.initials: SS
authors.lastname: Sheridan
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000393:Air Pollutants / Q000633:toxicity*; D000397:Air Pollution / Q000706:statistics & numerical data*; D002170:Canada; D002947:Cities / Q000706:statistics & numerical data; D005740:Gases / Q000633:toxicity*; D006801:Humans; D008875:Middle Aged; D009026:Mortality; D014887:Weather
chemical_list: D000393:Air Pollutants; D005740:Gases
keywords: AIC; Acute health effects; Air pollutants; Akaike′s Information Criteria; CO; DM; DP; DT; GLM; MM; MP; MT; NO(2); O(3); PM; PWM; RR; Relative mortality risk; SO(2); Synoptic scale classification; TR; Weather types; carbon monoxide; dry moderate; dry polar; dry tropical; generalized linear model; moist moderate; moist polar; moist tropical; nitrogen dioxide; ozone; particulate matter; population weighted mean; relative mortality risk; sulphur dioxide; transitional