Tracer element for indoor PM2.5 in China migrated from outdoor

doi:10.1016/j.atmosenv.2017.12.034

Atmospheric Environment

Volume 176, March 2018, Pages 171-178

https://doi.org/10.1016/j.atmosenv.2017.12.034 Get rights and content

Highlights

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Iron was proved to be a suitable tracer of outdoor PM_2.5 in China.
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Sulfur or nickel was not a suitable tracer for China.
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102 pairs of indoor and outdoor PM_2.5 samples were analyzed in Beijing.
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Two-thirds of the indoor PM_2.5 derives from outside.

Abstract

Sulfur and nickel have been widely used as tracers of outdoor PM_2.5 (particulate matter with an aerodynamic diameter ≤ 2.5 μm) in the United States and Europe; however, their feasibility as tracers has not been verified yet in China. We aim to verify whether sulfur or nickel could be used as a tracer element and, if not, to identify a suitable tracer element for outdoor PM_2.5 in China. We conduct two types of experiments, namely, preliminary and main-study experiments. We analyze 102 pairs of indoor and outdoor PM_2.5 samples in Beijing. The correlation between the I/O (indoor/outdoor) ratio of an element and the I/O ratio of total PM_2.5 is one of the criteria used to test whether this element can be used as a tracer element. The average concentrations of nickel are found to be below the detection limits in both preliminary and main-study tests. Thus, nickel cannot be used as a tracer element in China. Based on the correlations of elemental I/O ratios and the I/O ratio of total PM_2.5 in the preliminary and main-study tests, sulfur also cannot be used as a tracer element; however, it should be feasible to use iron as a tracer element in Beijing according to the test results. The estimated infiltration factor obtained by using iron as tracer is extremely consistent with the calculations based on the mass balance model. In summary, iron is found to be more suitable as a tracer for outdoor PM_2.5 in Beijing than sulfur or nickel.

Graphical abstract

Introduction

Numerous epidemiological studies have been conducted on the associations between exposure to PM_2.5 (particulate matter with an aerodynamic diameter ≤ 2.5 μm) and adverse health effects including respiratory infections, cardiopulmonary disorders, ischemic heart disease, and lung cancer (Anenberg et al., 2010, Brauer et al., 2012, Lim et al., 2012, van Donkelaar et al., 2010, Wu et al., 2014). However, a limitation of most of these studies was that outdoor PM_2.5 concentrations were used to estimate the population exposure, which apparently overlooks the fact that people spend approximately 90% of their time indoors (Klepeis et al., 2001). In most previous epidemiological studies, there has been virtually no differentiation between exposure to particles of outdoor origin and those generated indoors, and failure to account for related exposure variations in epidemiologic studies can lead to exposure misclassifications and bias in the epidemiologic results (Allen et al., 2012, Goldman et al., 2012, Ji and Zhao, 2015, Kioumourtzoglou et al., 2014, Shi et al., 2017).

The fraction of outdoor PM_2.5 that migrates into the indoor environment and remains suspended is represented by the infiltration factor. The infiltration factor can be an important tool for distinguishing the outdoor PM_2.5 exposure from total personal exposure. The infiltration factor varies with the building characteristics, window opening state, seasons, and so forth (Chen and Zhao, 2011). As the infiltration factor cannot be measured directly, it is generally estimated by the dynamic or steady-state solution to the indoor PM_2.5 mass balance equation (Diapouli et al., 2013). Alternatively, the infiltration factor can be evaluated by employing a PM constituent, with no indoor sources, as a tracer element of indoor PM that originated outside. The infiltration surrogates show good agreement, and the method is easy to apply when chemical composition data are available (Diapouli et al., 2013). Sulfur has been used in several studies as a tracer of outdoor PM_2.5 to estimate the infiltration factor (Allen et al., 2012, Cohen et al., 2009, Meng et al., 2005, Sarnat et al., 2002, Wallace and Williams, 2005). Long and Sarnat (2004) focused on six elements, namely, sulfur, nickel, zinc, iron, potassium, and silicon that were detected consistently in both indoor and outdoor samples, and the authors proposed that several elements, particularly nickel, could serve potentially accurate tracers for the infiltration of total PM_2.5 mass- and size-resolved particles into residential buildings.

In the United States and European cities, sulfur or other elements have been employed as surrogates for outdoor PM_2.5 (Diapouli et al., 2013); however, no study has verified yet whether sulfur could be a tracer element of outdoor PM_2.5 in China. Therefore, we aimed to verify whether sulfur or nickel could serve as such a tracer element. We conducted preliminary experiments in 14 residences, and 28 kinds of elements were analyzed to determine which elements may be treated as tracer elements, i.e., surrogates of infiltration. Then, we conducted a main-study experiments, 88 pairs of tests were conducted and five kinds of elements were analyzed according to the results of preliminary experiments and the literature review. The elements and the total PM_2.5 concentrations were analyzed, and the feasibility of using each of the elements as the tracer element for outdoor PM_2.5 was compared. In addition, the data were used to examine the infiltration factor for outdoor PM_2.5 and the contributions of the PM_2.5 that originated outdoors to the total indoor PM_2.5.

Section snippets

Preliminary experiments

Fourteen families were recruited to participate in the preliminary tests; all voluntarily agreed to engage after the participating requirements had been explained to them. The families were residents in the urban and suburb districts of Beijing (Haidian district, Chaoyang district, Xicheng district, Fengtai district and Fangshan distract), within the sixth ring road that circles the capital city of China. From November 2015 to March 2016, we sampled each participating house once during a heavy

Indoor–outdoor associations for preliminary experiments

The indoor and outdoor mass concentrations of PM_2.5 and 28 elements were analyzed, and the results are shown in Table 1. The mean indoor and outdoor concentrations of PM_2.5 were 146.8 and 254.8 μg/m³, respectively, for the 14 samples. The mean indoor mass concentrations of the 28 elements ranged from 8.8 ng/m³ to 3.28 μg/m³. For 19 kinds of elements with an average concentration below 100 ng/m³, their average concentrations were all below the detection limits except for aluminum, magnesium, and

Conclusions

Our study proved that although sulfur is commonly used in other countries, iron would be an ideal tracer element for outdoor PM_2.5 in China. By using the I/O ratio of iron, we analyzed the infiltration of outdoor PM_2.5 and the contribution of outdoor PM_2.5 to indoor PM_2.5 where indoor sources were present. We found that nearly two-thirds of the indoor PM_2.5 was derived from the outside.

In view of iron being identified as a suitable tracer element in China, we analyzed the contributions of

Competing financial interests

The authors declare that they have no competing financial interests.

Acknowledgments

This work was supported by the National Key Research and Development Plan of the Ministry of Science and Technology of China through Grant No. 2016YFC0700500, by the funding received from the Innovative Research Groups of the National Natural Science Foundation of China [No. 51521005] and by grants from the National Natural Science Foundation of China [Nos. 91543112, 81571130090]. We greatly appreciated the volunteer families participating in this work.

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Tracer element for indoor PM2.5 in China migrated from outdoor

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Preliminary experiments

Indoor–outdoor associations for preliminary experiments

Conclusions

Competing financial interests

Acknowledgments

Atmos. Environ.

Environ. Pollut.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Lancet

Environ. Pollut.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Environ. Pollut.

Sci. Total Environ.

Environ. Res.

Modeling the residential infiltration of outdoor PM2.5 in the multi-ethnic study of atherosclerosis and air pollution (MESA air)

Environ. Health Perspect.

An estimate of the global burden of anthropogenic ozone and fine particulate matter on premature human mortality using atmospheric modeling

Environ. Health Perspect.

Exposure assessment for estimation of the global burden of disease attributable to outdoor air pollution

Environ. Sci. Technol.

PM2.5 and Environment

Approach to estimating participant pollutant exposures in the multi-ethnic study of atherosclerosis and air pollution (MESA air)

Environ. Sci. Technol.

Tracer element for indoor PM_2.5 in China migrated from outdoor

Modeling the residential infiltration of outdoor PM_2.5 in the multi-ethnic study of atherosclerosis and air pollution (MESA air)