Elsevier

Environmental Pollution

Volume 253, October 2019, Pages 190-198
Environmental Pollution

The impact of household air cleaners on the chemical composition and children's exposure to PM2.5 metal sources in suburban Shanghai

https://doi.org/10.1016/j.envpol.2019.07.003Get rights and content

Highlights

  • Six sources of elements in indoor, outdoor, and personal exposure PM2.5 were found.

  • Air cleaner can reduce indoor concentrations of elements from most PM2.5 sources.

  • Personal exposure to some elements and sources was reduced by the air cleaner.

Abstract

Increased public awareness of the health impacts of atmospheric fine particulate matter (PM2.5) has led to increased demand and deployment of indoor air cleaners. Yet, questions still remain about the effectiveness of indoor air cleaners on indoor PM2.5 concentrations and personal exposure to potentially hazardous components of PM2.5. Metals in PM2.5 have been associated with adverse health outcomes, so knowledge of their sources in urban indoor and outdoor areas and how exposures are influenced by indoor air cleaners would be beneficial for public health interventions. We collected 48-h indoor, outdoor, and personal PM2.5 exposure samples for 43 homes with asthmatic children in suburban Shanghai, China during the spring months. Two sets of samples were collected for each household, one set with a functioning air filter placed in the bedroom (“true filtration”) and the other with a non-functioning (“sham”) air cleaner. PM2.5 samples were analyzed for elements, elemental carbon, and organic carbon. The major sources of metals in PM2.5 were determined by Positive Matrix Factorization (PMF) to be regional aerosol, resuspended dust, residual oil combustion, roadway emissions, alloy steel abrasion, and a lanthanum (La) and cerium (Ce) source. Under true filtration, the median indoor to outdoor percent removal across all elements increased from 31% to 78% and from 46% to 88% across all sources. Our findings suggest that indoor air cleaners are an effective strategy for reducing indoor concentrations of PM2.5 metals from most sources, which could translate into improved health outcomes for some populations.

Introduction

Metals constitute a small fraction of PM2.5 mass but are an important PM component associated with adverse health outcomes. Several in-vitro studies have shown that transition metals are associated with increased cellular reactive oxygen species, which can induce cellular oxidative stress and inflammation (Brehmer et al., 2019; Shafer et al., 2010; Shuster-Meiseles et al., 2016). Elevated PM2.5 are a major health concern in China, where ambient PM2.5 concenrations in some regions can reach annual averages as high as 95 μg m−3, nearly five times higher than the World Health Organization's 24-h guideline of 20 μg m−3 (Ma et al., 2014; WHO, 2006). PM2.5 metal concentrations are highest in urban centers that contain numerous anthropogenic sources of PM2.5 including vehicle exhaust and coal burning (Chen et al., 2016; Li et al., 2016; Xu et al., 2012). In Shanghai, potentially hazardous metals like chromium and manganese have been reported at concentrations 3 to 6 times higher than those found in some cities in Europe and the United States (Duan and Tan, 2013; Wang et al., 2013; Wiseman and Zereini, 2014). Given the adverse health outcomes associated with exposure to PM2.5 and its chemical components, effective intervention strategies aimed to reduce exposure to PM2.5 must be investigated.

The indoor environment may offer some protection from potentially hazardous outdoor PM2.5 sources like traffic emissions and coal combustion; however, severe outdoor pollution can infiltrate the indoor environment and significant exposures to potentially hazardous PM may still occur (Wang et al., 2016). The home environment does provide a setting for control of PM contaminants generated both indoors and outdoors. Methods to improve indoor air quality include measures that prevent the infiltration of outdoor pollution (e.g. increased insulation, improved HVAC systems) and remove indoor pollution (e.g. ventilation hoods). Indoor air filtration systems, like air cleaners with high-efficiency particulate air (HEPA) filters, are one common approach to control contaminants. Studies have found that HEPA filters are effective at reducing indoor concentrations of PM2.5 and may improve cardiovascular outcomes in some population groups, but not others (Fisk, 2013; Kelly and Fussell, 2019). Since the potential health impacts of PM2.5 may vary by source and chemical composition, these studies need to be replicated using detailed chemical analyses and source apportionment methods. Additionally, as households are not the only indoor environment where personal exposure to PM occurs, it is important to understand the limitations of remediation using a household air cleaner.

Positive matrix factorization (PMF) is a quantitative source apportionment tool that has been applied to PM2.5 samples from various settings around the world (Chuang et al., 2016; B. Liu et al., 2017; Liu et al., 2018; Zhang et al., 2015). The US Environmental Protection Agency (EPA) PMF 5.0 model contains 3 error estimation methods that aid in the selection of an optimal model solution (Brown et al., 2015). To our knowledge, no study has employed quantitative source apportionment methods with samples collected from an intervention study. Source contributions derived from the EPA PMF 5.0 model that includes chemical measurements from an intervention study may provide more detailed information on the effectiveness of the intervention.

This study was conducted to: (a) characterize PM2.5 bound elements and some bulk components in the context of an air cleaner intervention; (b) determine the sources of the elements in indoor, outdoor, and personal PM2.5 exposure samples; and (c) evaluate the effectiveness of air cleaners on reducing personal exposure to PM2.5 elements and their sources. A study of this design will further inform public health intervention strategies that aim to reduce personal exposure to PM2.5 air pollution.

Section snippets

Sampling

We enrolled 43 children ages 5–14 with physician diagnosed asthma to participate in our study. Sample collection took place in the Shanghai suburb of Songjiang, China from February 14 to April 27, 2017. Integrated 48-hr indoor, outdoor, and personal PM2.5 exposure samples were collected on 37 mm PTFE (Teflon) filters (Zeflour, Pall Laboratory, USA). Additional samples were collected on 37 mm quartz filters for indoor and outdoor characterization of organic and elemental carbon. Stationary

PM2.5 bulk composition

The mass concentrations and indoor to outdoor removal of PM2.5 mass, organic matter, elemental carbon, dust, sulfate, and trace elements (sum of ICPMS quantified elements not included in the dust calculation) are shown in Fig. 1 and Table 1. Arithmetic mean (AVG ± STD) indoor PM2.5 mass concentrations were lower (Wilcoxon signed-rank test p-value < 0.01) indoors under true filtration (15 ± 9.6 μg m−3) compared to sham filtration (34 ± 17 μg m−3). Outdoor and personal PM2.5 exposure mass

Conclusion

The results from our study show that indoor air cleaners were effective at reducing the indoor concentrations of all sources of metals except for the alloy steel abrasion and La and Ce source. These findings show that air cleaners can create a healthier indoor environment by reducing indoor concentrations of sources that contain potentially hazardous elements in PM2.5. Populations that spend a significant amount of time in indoor environments without a PM2.5 filtration system may benefit from a

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Acknowledgements

This work was made possible by Jiaqi Sun (Tsinghua University), field staff, and participants in Shanghai. We also thank Pam Skaar, Angela Albrech, and Robel Kebede from the Wisconsin State Laboratory of Hygiene for assisting with sample analysis and data processing. This work was funded by Underwriters Laboratory (UL) and the National Natural Science Foundation of China (51420105010). Opinions and findings reflect the views of the author(s), and do not necessarily reflect the views of the

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