title: Synergy between particles and nitrogen dioxide on emergency hospital admissions for cardiac diseases in Hong Kong.
abstract: BACKGROUND
  Ambient air pollution is a complex mixture of particles and gaseous pollutants. Epidemiological studies are moving toward a multipollutant approach, requiring an understanding of possible interactions among the pollutants. We aim to estimate the joint effects of particles with an aerodynamic diameter less than 10 μm (PM10) and nitrogen dioxide (NO2) on emergency hospital admissions for cardiac diseases, and to explore the possible interactions between PM10 and NO2.
  
  
  METHODS
  We collected daily time series data from 1998 to 2007 on emergency hospital admissions for cardiac diseases in Hong Kong, as well as PM10 and NO2 concentrations. Generalized additive Poisson model was used to examine the relationship between air pollution and hospital admissions. We then used three parallel time series approaches (bivariate response surface model, joint effect model and parametric stratified model) to explore the possible interactions between PM10 and NO2.
  
  
  RESULTS
  Results showed the greatest joint effect of PM10 and NO2 on emergency cardiac hospitalizations when PM10 and NO2 concentrations were both at high levels. The effect of PM10 was significantly greatest on the days with high NO2 level, and vice versa. A 10 μg/m(3) increase of lag0 PM10 and NO2 was associated with an increase of emergency cardiac hospitalizations by 0.55% (95% CI: 0.29-0.80%) and 1.20% (95% CI: 0.87-1.53%) respectively, when the other pollutant was at high level.
  
  
  CONCLUSIONS
  We found consistent synergistic interaction between PM10 and NO2 on emergency cardiac hospitalizations in Hong Kong. These findings contribute to the development of a new paradigm for multipollutant air quality management.
authors.affiliation: School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, China. Electronic address: iyu@cuhk.edu.hk.
authors.forename: Ignatius Tak-sun
authors.initials: IT
authors.lastname: Yu
authors.forename: Hong
authors.initials: H
authors.lastname: Qiu
authors.forename: Xiaorong
authors.initials: X
authors.lastname: Wang
authors.forename: Linwei
authors.initials: L
authors.lastname: Tian
authors.forename: Lap Ah
authors.initials: LA
authors.lastname: Tse
mesh_terms: D000397:Air Pollution / Q000032:analysis*; D004630:Emergencies; D006331:Heart Diseases / Q000453:epidemiology*; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008962:Models, Theoretical; D009585:Nitrogen Dioxide / Q000032:analysis*; D052638:Particulate Matter / Q000032:analysis*; D010343:Patient Admission / Q000706:statistics & numerical data*
chemical_list: D052638:Particulate Matter; D009585:Nitrogen Dioxide
keywords: APHEA; APHENA; Air Pollution and Health: a Combined European and North American Approach; Air Pollution and Health: a European Approach; Cardiac disease; ERR; Emergency hospital admission; GAM; IHD; NO(2); PACF; PM(10); Synergy; excess relative risk; generalized additive model; ischemic heart diseases; lag n days; lag(n); nitrogen dioxide; partial autocorrelation function; particles with an aerodynamic diameter less than 10μm