Size-Segregated Particle Number Concentrations and Respiratory Emergency Room Visits in Beijing, China

Article excerpt

BACKGROUND: The link between concentrations of particulate matter (PM) and respiratory morbidity has been investigated in numerous studies.

OBJECTIVES: The aim of this study was to analyze the role of different particle size fractions with respect to respiratory health in Beijing, China.

METHODS: Data on particle size distributions from 3 ran to 1 [micro]M; [PM.sub.10] (PM [less than or equal to] 10 [micro]m), nitrogen dioxide ([NO.sub.2]), and sulfur dioxide concentrations; and meteorologic variables were collected daily from March 2004 to December 2006. Concurrently, daily counts of emergency room visits (ERV) for respiratory diseases were obtained from the Peking University Third Hospital. We estimated pollutant effects in single- and two-pollutant generalized additive models, controlling for meteorologic and other time-varying covariates. Time-delayed associations were estimated using polynomial distributed lag, cumulative effects, and single lag models.

RESULTS: Associations of respiratory ERV with [NO.sub.2] concentrations and 100-1,000 nm particle number or surface area concentrations were of similar magnitude--that is, approximately 5% increase in respiratory ERV with an interquartile range increase in air pollution concentration. In general, particles < 50 nm were not positively associated with ERV, whereas particles 50-100 nm were adversely associated with respiratory ERV, both being fractions of ultrafine particles. Effect estimates from two-pollutant models were most consistent for [NO.sub.2].

CONCLUSIONS: Present levels of air pollution in Beijing were adversely associated with respiratory ERV. [NO.sub.2] concentrations seemed to be a better surrogate for evaluating overall respiratory health effects of ambient air pollution than [PM.sub.10] or particle number concentrations in Beijing.

KEYWORDS: emergency room visits, particle number concentration, particle surface area concentration, particulate matter, short-term effects, time-series analyses, ultrafine particles. Environ Health Perspect 119:508-513 (2011). doi:10.1289/ehp.1002203 [Online 30 November 2010]

There is consistent evidence that particulate matter (PM) with an aerodynamic diameter < 10 [micro]m or 2.5 urn ([PM.sub.10] or [PM.sub.2.5], respectively) is adversely associated with respiratory morbidity and mortality (Alfaro-Moreno et al. 2007; Health Effects Institute 2003; Pope and Dockery 2006). Some findings suggest that associations are stronger for finer than for coarser particles (Kan et al. 2007; Peng et al. 2008; Wichmann et al. 2000) and that there are qualitative differences between the health effects of different iiar-ide size tiucrions (Samuelsen et al. 2009). Physicochemical parameters such as size, shape, distribution, number, and volume of airborne particles determine the potential to induce inflammatory injury, oxidative damage, and other biological effects, which are all stronger for smaller-size fractions of particles (Oberdorster et al. 2005; Valavanidis et al. 2008). Ultrafine particles (UFP; particles with a diameter < 100 nm) may contribute more than other particle size fractions to the observed health effects, because they dominate total particle number and surface area concentrations and have a high deposition efficiency in the pulmonary region (Delfino et al. 2005; Frampton 2001; Wichmann 2007).

Because of the limited availability of measurement data, few epidemiologic studies have investigated associations between particle number concentrations in different size ranges and daily respiratory morbidity or mortality, and their findings have been inconsistent. Wichmann et al. (2000) reported in a study conducted in Erfurt, Germany, with a population of approximately 200,000, that associations with total mortality were comparable for an interquartile range (IQR) increase in UFP [relative risk (RR) = 4.1%; 95% confidence interval (CI), 0.1-8.2] and [PM. …