Elsevier

Science of The Total Environment

Volume 409, Issue 24, 15 November 2011, Pages 5196-5204
Science of The Total Environment

Sub-micrometer particulate air pollution and cardiovascular mortality in Beijing, China

https://doi.org/10.1016/j.scitotenv.2011.08.023Get rights and content

Abstract

Background

While the link between particulate matter and cardiovascular mortality is well established, it is not fully investigated and understood which properties of the aerosol might be responsible for the health effects, especially in polluted mega-city areas.

Objectives

Our goal was to explore the association between daily cardiovascular mortality and different particle metrics in the sub-micrometer range in Beijing, China.

Methods

We obtained daily counts of cause-specific cardiovascular deaths in the Beijing urban area for the period March 2004 to August 2005. Concurrently, continuous measurements of particle number size distributions were performed. Particle number concentrations (NC) between 0.003 μm and 0.8 μm were converted to particle mass and surface area concentrations assuming spherical particles. Semi-parametric Poisson regression models adjusting for trend, seasonality, day of the week, and meteorology were used to estimate immediate, delayed and cumulative particle effects. Additionally, effect modification by air mass origin was investigated.

Results

We observed associations between daily cardiovascular mortality and particle NC for a 2-days delay. Moreover, nearly all particle metrics showed 2-days delayed associations with ischemic heart disease mortality. The strongest association was found for particle NC in the size range 0.03–0.1 μm (7.1% increase in daily mortality with a 95%-confidence interval of 2.9%–11.5%, per an increase of 6250 particles/cm3). Results for surface and mass concentrations with a lag of two days indicated effect modification by air mass origin, whereas effects of particle NC were not modified.

Conclusions

Results show an elevated risk of cardiovascular mortality in Beijing from short-term exposure to particulate air pollution in the sub-micrometer range. Results also indicate that locally produced smaller particles and regionally transported particles may exhibit different effects in Beijing.

Highlights

► We investigated the effects of smaller particles on cardiovascular mortality in Beijing, China. ► Emphasis was on whether associations are due to particle number, mass, or surface area. ► Particle number concentrations in the size range 0.03–0.1 μm showed most consistent associations. ► Surface and mass concentrations may be modified by air mass origin. ► Effects of particle number concentrations were not modified by air mass origin.

Introduction

Cardiovascular morbidity and mortality have been associated with mass concentrations of particulate matter (PM) with an aerodynamic diameter smaller than 10 μm or 2.5 μm (PM10 or PM2.5, respectively) (Brook et al., 2010, Pope and Dockery, 2006). Nevertheless, questions remain regarding the physical or chemical properties of PM responsible for the health effects. Besides chemical composition, particle characteristics like size, number concentration, and surface area are discussed to determine the potential to induce inflammatory injury, oxidative damage, and other biological effects (Brook, 2008, Valavanidis et al., 2008).

In particular, ultrafine particles (particles with an aerodynamic diameter less than 100 nm; UFP) may contribute to the observed health effects because of their high particle number concentrations and larger active surface area; thus, having a high deposition efficiency in the pulmonary region (Brook, 2008, Delfino et al., 2005, Pekkanen and Kulmala, 2004, Peters et al., 2006). UFP can be further divided into two sub-fractions: Nucleation mode particles and Aitken mode particles. Nucleation mode particles are often defined as particles with an aerodynamic diameter less than < 0.03 μm, whereas Aitken mode particles are then defined as particles with an aerodynamic diameter between 0.03 and 0.1 μm; see, for example, Halonen et al. (2009) or Peters et al. (2009) (it should be noted, however, that there are also studies using different size ranges for Nucleation mode and Aitken mode particles; see, for example, Yue et al., 2009, Branis et al., 2010). Both sub-fractions differ in dynamics and may also have varying effects on health. Nucleation mode particles mainly result from gas-to-particle conversion of different chemical compounds. Aitken mode particles, on the other hand, are directly emitted from combustion processes, such as soot particles from car traffic. They may also result from condensational growth and coagulation of nucleation mode particles. Aerosols in the accumulation mode (0.1–0.8 μm; ACP) are generally produced by the coagulation of smaller particles and by the heterogeneous nucleation of condensable vapors onto existing aerosol particles.

Due to the limited availability of appropriate measurement data, there are only few epidemiological studies on the short-term associations between daily cardiovascular mortality and more accurately size-segregated particles (Atkinson et al., 2010, Branis et al., 2010, Halonen et al., 2009, Peters et al., 2009, Stölzel et al., 2003). Nearly all studies on health effects of smaller particles have been conducted in North America and Europe; there remains a need for replicating these findings in China, as there are different concentration levels. There might be also differences in specific sources and their proportional contributions to the air pollution mixture, which might influence size distribution and chemical composition of particles and the associations between particles and human health.

This study aimed to investigate whether daily changes in ambient concentrations of particle size fractions in the sub-micrometer range are associated with cause-specific cardiovascular mortality in different age groups in Beijing, China. Moreover, we aimed to better delineate whether particle number, mass, or surface area concentrations may be responsible for the associations. Additionally, we investigated modifications of air pollution effects by air mass origin defined by backward trajectories.

Section snippets

Study area and period

The study was conducted in the urban area of Beijing, China, from March 4, 2004 to August 31, 2005 (546 days). Beijing is located about 150 km southeast of the Bohai Sea, and is surrounded by mountains in the north, northwest, and west. In 2005, the Beijing urban area comprised eight districts with a total area of about 1368 km2 and had a population size of approximately 10 million inhabitants (Beijing Municipal Bureau of Statistics, 2006) [Appendix A, Fig. A.1].

Mortality data

Cardiovascular death count data for

Descriptives

Overall, there were 15,769 cardiovascular deaths during the study period from March 4, 2004 to August 31, 2005. Ischemic heart diseases and cerebrovascular diseases were the two major death causes for cardiovascular mortality; each category accounted for around 42% of the deaths. Elderly people (≥ 65 years) accounted for at least 75% for all causes of death.

Descriptive parameters of death counts, particle metrics, and meteorological data are provided in Table 1. Daily death counts and

Discussion

We observed adverse associations between particle NC and cardiovascular mortality for a 2-days delay. Moreover, all particle parameters except particle NC below 30 nm showed 2-days-delayed associations with ischemic heart disease mortality. The strongest association was found for NC of particles in the size range 0.03–0.1 μm. This association also did not change when adjusting for other particle metrics. Mortality effects of particle NC were not modified by air mass origin. In contrast, results

Conclusions

This analysis showed an elevated risk of cardiovascular mortality in Beijing from short-term exposure to particulate air pollution in the sub-micrometer range. Results especially point to a delayed association between particle NC and cardiovascular mortality. Results also indicate that locally produced ultrafine particles and regionally transported ACP may exhibit different effects in Beijing.

Disclosure statement

The authors declare they have no competing financial interests.

Acknowledgments

This research was funded by the German Research Foundation (DFG) (grants PE 1156/1-2 and WI 621/16-1). Parts of this work were funded by a scholarship being awarded to Liqun Liu (File no. 2008601213) under the State Scholarship Fund by the China Scholarship Council (CSC). We would like to thank the Institute for Tropospheric Research (IfT) for providing guidance of the particulate measurements.

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