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Seasonal and Diurnal Air Pollution from Residential Cooking and Space Heating in the Eastern Tibetan Plateau Ellison M Carter, Scott Archer-Nicholls, Kun Ni, Alexandra M Lai, Hongjiang Niu, Matthew H Secrest, Sara M Sauer, James J. Schauer, Majid Ezzati, Christine Wiedinmyer, Xudong Yang, and Jill Baumgartner Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b00082 • Publication Date (Web): 28 Jun 2016 Downloaded from http://pubs.acs.org on June 28, 2016
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Seasonal and Diurnal Air Pollution from Residential Cooking and Space Heating in the
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Eastern Tibetan Plateau
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Ellison Cartera, Scott Archer-Nichollsb, Kun Nic, Alexandra M. Laid, Hongjiang Niuc, Matthew
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H. Secrestg, Sara M. Sauerg, James J. Schauerd,e, Majid Ezzatif, Christine Wiedinmyerb, Xudong
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Yangc*, Jill Baumgartnera,g,* a
Institute on the Environment, University of Minnesota, St. Paul MN, USA National Center for Atmospheric Research, Boulder, CO, USA c Department of Building Science, Tsinghua University, Beijing, China d Department of Civil and Environmental Engineering, University of Wisconsin, Madison, WI, USA e Environmental Chemistry and Technology Program, University of Wisconsin, Madison, WI, USA f MRC-PHE Center for Environment and Health, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, UK g Institute for Health and Social Policy and Department of Epidemiology, Biostatistics & Occupational Health, McGill University, Montréal QC, Canada b
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*
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(1) Xudong Yang; Department of Building Science, Tsinghua University, Beijing Haidian
co-corresponding authors
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District, 100084, China; (+86) 10 62788845;
[email protected] 11
(2) Jill Baumgartner; Institute for Health and Social Policy and Department of Epidemiology,
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Biostatistics and Occupational Health, 1130 des Pins Avenue Ouest, Montréal, Québec H3A 1A3
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Canada; (+001) 514-398-6688;
[email protected] 14 15
Keywords: biomass burning, space heating, China, household air pollution, particulate matter,
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residential biofuel use, natural ventilation
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Abstract
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Residential combustion of solid fuel is a major source of air pollution. In regions where space
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heating and cooking occur at the same time and using the same stoves and fuels, evaluating air
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pollution patterns for household energy use scenarios with and without heating is essential to
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energy intervention design and estimation of its population health impacts, as well as the
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development of residential emission inventories and air quality models. We measured continuous
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and 48-h integrated indoor PM2.5 concentrations over 221 and 203 household-days, and outdoor
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PM2.5 concentrations on a subset of those days, in summer and winter, respectively, in 204
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households in the eastern Tibetan Plateau that burned biomass in traditional stoves and open
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fires. Using continuous indoor PM2.5 concentrations, we estimated mean daily hours of
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combustion activity, which increased from 5.4 hours day-1 (95% CI: 5.0, 5.8) in summer to 8.9
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hours day-1 (95% CI: 8.1, 9.7) in winter, and effective air exchange rates, which increased from
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15 ± 7 h-1 in winter to 18 ± 9 h-1 in summer. Indoor geometric mean 48-h PM2.5 concentrations
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were over two times higher in winter (252 µg/m3; 95% CI: 215, 295) than in summer
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(101 µg/m3; 95%: 91, 112), whereas outdoor PM2.5 levels had little seasonal variability.
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Introduction
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Air pollution from residential combustion of solid fuel (i.e., biomass and coal) is a leading
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contributor to the global burden of disease1 and impacts regional and global climate.2,3,4
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Reductions in residential solid fuel emissions through less polluting fuels and stoves could
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improve air quality and population health. These reductions are particularly relevant to China,
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which has pressing air quality concerns and where an estimated 20% of the world’s solid fuel
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users reside.5,6
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Seasonality and diurnal variation in residential energy use, especially combustion activity
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associated with space heating, has been noted as a knowledge gap in existing exposure
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assessments7,8 and emissions inventories.9—12 In rural China, numerous studies have measured
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higher integrated area concentrations and personal exposures in winter than in summer,13—18
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which study authors attributed to space heating. Household energy use in these studies involved
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multiple fuels and stoves that serve multiple purposes, including cooking, water boiling, and
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space heating. These studies highlight the potential for exposure reduction estimates associated
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with cooking-focused interventions to over- or under-report the impacts of these interventions,
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depending on the extent to which fuel and stove use for heating are also modified, and the need
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for repeated seasonal measurements throughout intervention studies.
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Quantifying stove use using temperature sensors has been successfully done with stationary
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stoves19 and is well suited for monitoring if a stove was used or not.20—22 However, temperature-
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sensors are not as well suited to measure the intermittent use of open fires and of movable fire
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pans that are common throughout China.16—18 They can be challenging to implement at the scale
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of several hundred households or more, each with numerous, multi-purpose stove-fuel
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combinations.13,14,18 Further, the use of a single stove for more than one purpose limits the
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interpretability of stove temperature data, even when paired with questionnaires. Analysis of
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indoor and outdoor air quality measurements to assess seasonal and daily patterns of combustion
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activity is an important complement to temperature-based stove use monitoring, especially in the
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context of intervention evaluation.
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Seasonal and daily patterns of residential energy use are also poorly represented in emission
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activity datasets.9,10 Previous emission inventory research in China and other parts of Asia
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suggests that residential solid fuel burning contributes the majority of total emitted
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anthropogenic carbonaceous aerosols.23—27 However, the magnitude of these emissions estimates
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is highly uncertain28—up to a factor of two29—as are their temporal distributions.30 Temporally
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resolved estimates of rural residential energy combustion based on field-collected measurements
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could reduce uncertainty in regional emission and emission reduction estimates, provide
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empirical data for model validation, and improve the estimates from air quality and population
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health models using them.7,11,12,31,32
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We conducted a study in 204 households in the eastern Tibetan Plateau that burned biomass in
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traditional stoves and intermittent open fires for cooking, water boiling, and space heating. We
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measured daily cooking fuel use and real-time indoor (kitchen) and outdoor particulate matter
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with aerodynamic diameter ≤ 2.5 µm (PM2.5) concentrations in summer and winter, estimated
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effective air exchange rates, and collected information on self-reported meals cooked and
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ventilation habits. We aimed to overcome the challenge of differentiating between combustion
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activity with and without space heating activity through analysis of continuous PM2.5 profiles
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collected during 48-h measurement periods. Using this analysis, we developed seasonal and
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diurnal patterns of biomass combustion and PM2.5 pollution.
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Methods
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Study Site and Population. Our study site on the eastern edge of the Tibetan Plateau in Sichuan
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Province has a cool and temperate climate, with monthly precipitation averages ranging from 6
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mm in December to 238 mm in July and annual total precipitation reaching 933 mm on average
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(Climate-Data.org). The average monthly high/low temperatures in July and January are
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28°C/16°C and 9°C/1°C, respectively. We enrolled 204 households from four administrative
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villages in Beichuan County, Sichuan. Homes are at 1000-1450m above sea level and 80 km
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northwest of the provincial capital of Chengdu. Eligible households were those that self-reported
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cooking with biomass fuel and that had at least one woman eligible for enrolment into a separate
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health study. Cooking fuel usage and indoor air quality measurements were conducted 10 May –
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14 August 2014 and 19 November – 9 February 2015. Village leaders and local staff assisted in
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identifying eligible homes. We obtained oral informed consent from all participants. Study
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protocols were approved by Institutional Review Boards at the University of Minnesota, USA,
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McGill University, Canada, and Tsinghua University, China.
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Household energy use. The housing characteristics, ventilation practices, and household fuels
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and stoves in our study site are described by Shan et al.33 and Ni et al.18 Briefly, all kitchens are
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indoors and most have traditional biomass chimney stoves with two combustion chambers
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(Supporting Information Figure S1), which are used for both cooking and heating activities.
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Nearly 90% of homes reported using wood as their primary cooking fuel. The remaining 10%
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reported using gaseous fuels (i.e. liquefied petroleum gas and biogas) or electricity as their
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primary fuel and biomass as secondary. Over 95% of homes reported using wood or wood-
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charcoal as their primary heating fuel during cooler months; of these, 98% reported daily
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combustion of wood or wood-charcoal in traditional chimney stoves or in fire pans and open
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fires (Supporting Information Figure S1). The chimney stoves have low overall thermal
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efficiency (
