Coarse particles and mortality in three Chinese cities: The China Air Pollution and Health Effects Study (CAPES)

Abstract

Evidence concerning the health risks of coarse particles (PM_10-2.5) is limited. There have been no multi-city epidemiologic studies of PM_10-2.5 in developing Asian countries. We examine the short-term association between PM_10-2.5 and daily mortality in three Chinese cities: Beijing, Shanghai, and Shenyang. PM_10-2.5 concentrations were estimated by subtracting PM_2.5 from PM₁₀ measurements. Data were analyzed using the over-dispersed generalized linear Poisson models. The average daily concentrations of PM_10-2.5 were 101 μg/m³ for Beijing (2007–2008), 50 μg/m³ for Shanghai (2004–2008), and 49 μg/m³ for Shenyang (2006–2008). In the single-pollutant models, the three-city combined analysis showed significant associations between PM_10-2.5 and daily mortality from both total non-accidental causes and from cardiopulmonary diseases. A 10-μg/m³ increase in 1-day lagged PM_10-2.5 was associated with a 0.25% (95% CI: 0.08 to 0.42) increase in total mortality, 0.25% (95% CI: 0.10 to 0.40) increase in cardiovascular mortality, and 0.48% (95% CI: 0.20 to 0.76) increase in respiratory mortality. However, these associations became statistically insignificant after adjustment for PM_2.5. PM_2.5 was significantly associated with mortality both before and after adjustment for PM_10-2.5. In conclusion, there were no statistically significant associations between PM_10-2.5 and daily mortality after adjustment for PM_2.5 in the three Chinese cities.

Introduction

Ambient air pollution is a complex mixture composed of both solid particles and gaseous pollutants. Among various air pollutants, particulate matter (PM) often shows the strongest evidence for adverse health effects (Brunekreef and Holgate, 2002). PM can be characterized as discrete particles spanning several orders of magnitude in size: PM₁₀ (defined as particulate matter less than 10 μm in aerodynamic diameter); PM_2.5, also known as fine particles (defined as those particles less than 2.5 μm in aerodynamic diameter); and PM_10-2.5, also known as coarse particles (defined as those particles between 10 and 2.5 μm in aerodynamic diameter). Most prior studies have only used PM_2.5 or PM₁₀ as PM measurements, leaving the effects of other particle sizes – particularly PM_10-2.5 – not well understood (Pope and Dockery, 2006).

Compared with PM_2.5, PM_10-2.5 have different sources, composition and deposition mode in the human airway (Lippmann and Schlesinger, 2000, Wilson and Suh, 1997). In addition, findings from existing epidemiological studies of PM_10-2.5 have been limited and inconclusive (Brunekreef and Forsberg, 2005, Chang et al., 2011, Mallone et al., 2011); some studies found significant health hazards of PM_10-2.5, while others did not. The inadequate evidence of health effects of PM_10-2.5 had led the US Environmental Protection Agency (EPA) to reject a proposal to replace the existing daily PM₁₀ standard with daily PM_10-2.5. Furthermore, most studies of PM_10-2.5 were conducted in developed countries, with only a small number of studies conducted in Asia. As the results, there remains a need for studies in cities of developing countries, where characteristics of outdoor air pollution (e.g. air pollution level, chemical composition and size of particles, and fate and transport of pollutants), meteorological conditions, and socio-demographic status of local residents (e.g. disease pattern, age structure, and social economic status), may be different from developed countries.

As the largest developing country, China may have the worst PM pollution in the world (Kan et al., 2009). The current Chinese Air Quality Standard includes PM₁₀ only, and PM_2.5 and PM_10-2.5 are still not criteria pollutants. In the literature, only one study in China has investigated the health impact of PM_10-2.5 and this is due to lack of monitoring data (Kan et al., 2007). The objective of this paper is to examine the short-term associations between PM_10-2.5 and daily mortality in three Chinese cities – Beijing, Shanghai, and Shenyang. This study is a component of the “China Air Pollution and Health Effects Study” (CAPES) initiated by the China Ministry of Environmental Protection (Chen et al., 2011).