Research Size-Segregated Particle Number Concentrations and Respiratory Emergency Room Visits in Beijing, China Arne Marian Leitte,1 Uwe Schlink,1 Olf Herbarth,2 Alfred Wiedensohler,3 Xiao-Chuan Pan,4 Min Hu,5 Matthia Richter,1 Birgit Wehner,3 Thomas Tuch,3 Zhijun Wu,3,5 Minjuan Yang,4 Liqun Liu,4,6 Susanne Breitner,6 Josef Cyrys,6,7 Annette Peters,6 H.-Erich Wichmann,6,8 and Ulrich Franck1 1Core Facility Studies, Helmholtz Centre for Environmental Research–UFZ, Leipzig, Germany; 2University of Leipzig, Faculty of Medicine, Department of Environmental Medicine and Hygiene, Leipzig, Germany; 3Physics Department, Leibniz Institute for Tropospheric Research, Leipzig, Germany; 4Peking University, School of Public Health, Department of Occupational and Environmental Health, Beijing, People’s Republic of China; 5State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, People’s Republic of China; 6Institute of Epidemiology, Helmholtz Zentrum München—German Research Center for Environmental Health, Neuherberg, Germany; 7Environment Science Center, University of Augsburg, Augsburg, Germany; 8Department of Epidemiology, Ludwig-Maximilians-University, Munich, Germany : The link between concentrations of particulate matter (PM) and respiratory morbidity Background o Bjectivs has been investigated in numerous studies. : 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 nm to 1 mμ; PM 10 (PM ≤ 10 mμ), nitrogen dioxide (NO2), 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 meteoro- logic and other time-varying covariates. Time-delayed associations were estimated using polynomial distributed lag, cumulative effects, and single lag models. r esult : Associations of respiratory ERV with NO2 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 NO2. c onclusi : Present levels of air pollution in Beijing were adversely associated with respiratory ERV. NO2 concentrations seemed to be a better surrogate for evaluating overall respiratory health effects of ambient air pollution than PM10 or particle number concentrations in Beijing. k ey words : emergency room visits, particle number concentration, particle surface area concentra- tion, 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 mμ or 2.5 mμ (PM 10 or PM2.5, respec- tively) 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 particle size fractions (Samuelsen et al. 2009). Physicochemical parameters such as size, shape, distribution, number, and volume of airborne particles determine the potential to induce inflam- matory injury, oxidative damage, and other biological effects, which are all stronger for smaller-size fractions of particles (Oberdörster 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 parti- cle number and surface area concentrations 508 and have a high deposition efficiency in the pulmonary region (Delfino et al. 2005; Frampton 2001; Wichmann 2007). Because of the limited availability of meas- urement data, few epidemiologic studies have investigated associations between particle number concentrations in different size ranges and daily respiratory morbidity or mortal- ity, and their findings have been inconsistent. Wichmann et al. (2000) reported in a study conducted in Erfurt, Germany, with a popu- lation of approximately 200,000, that asso- ciations with total mortality were comparable for an interquartile range (IQR) increase in UFP [relative risk (RR) = 4.1%; 95% con- fidence interval (CI), 0.1–8.2] and PM2.5 (RR = 4.9%; 95% CI,1.1–8.8), whereas cause- specific mortality showed a somewhat stronger association with respiratory diseases compared with cardiovascular diseases and other causes. Peters et al. (1997) reported that inverse asso- ciations with peak expiratory flow (PEF) in asthmatic patients were stronger for an IQR increase in particle number concentrations of UFP than mass concentrations of fine particles (aerodynamic diameter 0.1–0.5 mμ). Penttinen et al. (2001) reported that daily mean par- ticle number concentrations, but not particle mass concentrations, were negatively associated with daily PEF deviations in adult asthmat- ics, whereas the strongest associations were found with particles in the ultrafine range. In a study conducted in Copenhagen, Denmark, Andersen et al. (2008) reported associations between pediatric asthma hospital admissions and IQR increases in accumulation-mode par- ticles (0.1–1 mμ), UFP (< 0.1 mμ), and nitro - gen oxide (NOx) concentrations. On the other hand, associations between PM and hospital admissions due to cardiovas- cular and respiratory disease in the elderly in Copenhagen appeared to be mediated mainly by PM10 or accumulation mode particles rather than urban background UFP (Andersen et al. 2008). In addition, Osunsanya et al. (2001) found no association between UFP and respiratory symptoms or PEF in adult patients with chronic airflow obstruction in Aberdeen, Scotland. Most studies of air pollution and health have been conducted in Western Europe or North America. Differences between Asian and Western populations in overall health status, lifestyle and age structure of the populations, and exposures to different air pollution mix- tures and levels might influence associations Address correspondence to A. Leitte, Core Facility Studien, Helmholtz Centre for Environmental Research – UFZ, Permoserstraße 15/04318 Leipzig, Germany. Telephone 49 (0) 341 235 1540. Fax: 49 (0) 341 235 451540. E-mail: arne.leitte@ufz.de Supplemental Material is available online (doi:10.1289/ehp.1002203 via http://dx.doi.org/). We thank all partners participating in this project, the Institute for Tropospheric Research for provid- ing guidance of the particulate measurements, the Third Hospital for providing the emergency room cases, and weatherundergound.com for providing the meteorologic data. This research was supported by the Deutsche Forschungsgemeinschaft (FR-1417/3-2) and the China National Natural Science Foundation (20420130348, 20637020). The authors declare they have no actual or potential competing financial interests. Received 24 March 2010; accepted 30 November 2010. ovlume 119 | number 4 | April 2011 • Environmental Health Perspectives