Article pubs.acs.org/est
Real-Time Particulate and CO Concentrations from Cookstoves in Rural Households in Udaipur, India Anna Leavey,† Jessica Londeree,‡,⊥ Pratiti Priyadarshini,§ Jagdeesh Puppala,§ Kenneth B. Schechtman,∥ Gautam Yadama,‡ and Pratim Biswas*,† †
Aerosol and Air Quality Research Laboratory, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, Campus Box 1180, St. Louis, Missouri 63130, United States ‡ George Warren Brown School of Social Work, Washington University in St. Louis, Campus Box 1196, St. Louis, Missouri 63130, United States § Foundation for Ecological Security, Udaipur Team, Opp Jyoti School, Fatehpura, Udaipur 313 001, Rajasthan, India ∥ Division of Biostatistics, Washington University School of Medicine, Campus Box 8067, St. Louis, Missouri 63110, United States S Supporting Information *
ABSTRACT: Almost 3 billion people around the globe use traditional three-stone cookstoves and open fires to warm and feed themselves. The World Health Organization estimates annual mortality rates from domestic solid fuel combustion to be around 4 million. One of the most affected countries is India. Quantifying pollutant concentrations from these cookstoves during different phases of operation and understanding the factors influencing their variability may help to identify where improvements should be targeted, enhancing indoor air quality for millions of the world’s most vulnerable people. Gas and particulate measurements were collected between June and August, 2012, for 51 households using traditional cookstoves, in the villages of Udaipur district, Rajasthan, India. Mean pollutant concentrations during steady-state mode were 4989 μm2 cm−3, 9835 μg m−3, and 18.5 ppm for lungdeposited surface area, PM2.5, and CO, respectively. Simple and multivariate regression analysis was conducted. Fuel amount, fuel diameter, duration of the cookstove run, roof-type, and the room dimension explained between 7% and 21% of the variability for the pollutant metrics. CO demonstrated weaker correlations with explanatory variables. Some of these variables may be indicative of socio-economic status and could be used as proxies of exposure in lieu of pollutant measurements, hence these variables may help identify which households to prioritize for intervention. Such associations should be further explored.
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INTRODUCTION Biomass fuels are cheap, relatively abundant, and CO2 neutral, provided they are harvested sustainably.1 Approximately two million tons of biomass are burned daily around the globe, in traditional three-stone cookstoves, open fires, or some type of improved cookstove (ICS), enabling around 2.8 billion people to warm and feed themselves.2,3 However, many of the pollutants emitted during incomplete combustion, which comprise a complex mixture of both aerosols and gas-phase species, have been classed as either irritants, allergens, carcinogens, neurotoxins, mutagens, or of inducing oxidative stress and inflammation.4 The harm inflicted by these noxious emissions is enhanced because of the poorly ventilated environments in which they are released. Recent estimates by the World Health Organization (WHO) and other leading experts put the 2010−2012 mortality rate from household air pollution (HAP) from solid fuel combustion at between 3.5 and 4.3 million, more than doubling previous estimates, and making it one of the highest risk factors for global disease © 2015 American Chemical Society
burden, ranked fourth behind high blood pressure, tobacco smoking, and alcohol use.5,6 Causes of mortality and morbidity from solid fuels include lower respiratory infections (for example pneumonia), ischemic heart disease (IHD), COPD, stroke, cataracts, asthma, and adverse pregnancy outcomes, including stillbirth and low birth weight.3,5 One of the most affected countries is India. According to the 2011 India Census, almost 63% of rural households use firewood, 12.3% use crop residue, and 10.9% use cowdung cakes for cooking,7 and fewer than 9% of households have access to ICS.2 In fact, more than 13% of deaths among children younger than 5 years old in 2012 have been attributed to HAP.6 Although the use of cleaner fuels is increasing, this is mainly among the higher income sectors of society and in urban areas, and burning biomass in cookstoves Received: November 10, 2014 Accepted: May 15, 2015 Published: May 18, 2015 7423
DOI: 10.1021/acs.est.5b02139 Environ. Sci. Technol. 2015, 49, 7423−7431
Article
Environmental Science & Technology Table 1. Experimental Test Plan Conducted at Each Householda test
description
duration (min)
rationale
L1_OR
outside prior to the lighting of the cookstove
5
outdoor baseline measurements
L2_IR
inside the household prior to the lighting of the cookstove during initial ignition: start-up mode
5
indoor baseline measurements
3−7
during steady-state mode cookstove has reached optimal conditions when the cookstove is extinguished
5−15
pollutant concentrations while cookstove is warming up pollutant concentrations during main operating mode to examine pollutant concentration patterns
L2_SU L2_SS L2_Ex
20
limitations may have been affected by other emission sources sometimes cookstoves were left smoldering difficult to know exact length of phase
cookstoves were not always extinguished
a
L1 = 1 m from the household wall; L2 = 1 m horizontal distance from the cookstove, 1 m height; OR = outdoor baseline; IR = indoor baseline; SU = start-up mode; SS = steady-state mode; Ex = extinguishing.
members. The average household income ranged from Rs. 10 000 to 25 000 (180−460 USD) per annum. Tribal communities dominate these remote areas, are among the poorest socio-economic group, and are dependent almost entirely upon agriculture and on solid fuel. The vast majority of households use wood, collected by women from nearby fields, and cowdung cakes. This work was performed in cooperation with the local Foundation for Ecological Security (FES) (Udaipur team). Measurements were conducted in 22 villages, and the number of households surveyed in each village ranged from 1 to 5. The selection of villages and households was largely at the discretion of FES and based on personal contacts either with FES employees or with villages that were being contacted by FES for other outreach programs. In order for a village to be included, FES staff had to consult all the village leaders and obtain permission. Only after permission was granted could the household selection begin. Household selection criteria included a willingness to participate, most frequently the decision of the male head of household. Eligibility requirements included cooking indoors, ideally on a traditional single pot cookstove. These cookstoves tend to be U-shaped, made of mud clay, and open on one side to facilitate the addition of fuel. Participants were also required to cook with either biomass, dung, or both, and any combination was acceptable; other types of supplemental fuel to help ignition were also frequently used. The objective of this study was capturing pollutant concentrations under real-world scenarios, and according to Zhang et al.,9 in-field measurements represent everyday cooking practices. Therefore, no attempt was made to control how the cookstove was operated, as long as the initial eligibility criteria were satisfied. The different household or fuel characteristics, all nonidentifying, were instead captured in a questionnaire for subsequent regression analysis. Finally, the woman had to be available to cook, and so measurements were conducted at times when the woman was not out collecting wood, and due to personnel and time constraints, this was not always during actual meal times, and so frequently only water for tea was boiled. Household Description. A household typically consisted of 1 or 2 rectangular rooms: a kitchen and a bedroom, and a small outdoor veranda. Walls tended to be constructed from mud bricks, and the floors also from mud. The cookstove was the main object in the kitchen and was generally installed in the corner of the room, by the wall adjacent to the front door. Sometimes it was located next to a window, and other times not. Windows and doors were always open as they could not be closed. Aside from the cookstove, rooms were essentially bare,
will remain the principal method of cooking food in rural India for the foreseeable future.8 With the exception of several field studies that have measured a range of particle metrics including particle number counts, particle number and mass size distributions, and chemical composition in rural households in China, Bangladesh, and Mexico,9−11 most studies tend to measure PM2.5 and CO,12−17 and aside from Sahu et al.,18 lung-deposited surface area (SA) has not been investigated. The inclusion of an SA metric would provide useful information on exposure risks given that SA is increasingly identified as an important dose metric for predicting proinflammatory responses in pulmonary toxicity studies.19−21 While many studies have conducted indoor measurements over 24- and 48-h time periods, this study aimed to measure lung-deposited SA, PM2.5 and CO concentrations from the burning of biomass and dung in traditional cookstovesimmediately prior to, during and immediately after cookstove operation. The aims were to quantify pollutant concentrations from each stage of operation, and to highlight the key parameters influencing these concentrations through simple and multivariate regression analysis, achieved with the help of questionnaire/survey data. Given the continued inaccessibility of ICS and cleaner fuels for the majority of rural Indian households, and the assertion that significant reductions in HAP are achievable without ICS or cleaner fuels,22 identifying those factors which influence HAP the most will help to identify where efforts should be targeted in order to improve the indoor air quality (IAQ) for millions of the world’s most vulnerable people. At the same time, these explanatory factors could be used as proxies of exposure in lieu of pollutant measurements, identifying which households should be prioritized for intervention. It is hoped that the results from this study will add a valuable contribution to existing studies.
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METHODS AND ANALYSIS Site Description. The city of Udaipur is situated close to the southern tip of Rajasthan, India’s largest state, located in the northwest of the country, and where up to 89% of households use biomass as their primary cooking fuel.23 Udaipur has a population of around 600 000, 55% of whom live below the poverty line.24 Villages within the two nearby tehsils of Gogunda and Jhadol were selected for the measurement campaign. Although these villages are approximately 10−45 km from Udaipur City, the hilly terrain makes access challenging, exacerbating their remoteness. Each village has between 50 and 200 households, and each household has between 2 and 12 7424
DOI: 10.1021/acs.est.5b02139 Environ. Sci. Technol. 2015, 49, 7423−7431
Article
Environmental Science & Technology
displayed on the laptop that was controlling the CO sensor. This ensured that the measurement and activity times matched on the Emissions Log Form, and so tests could be reliably compared. Standard quality assurance procedures were followed: all data were checked for completeness and cleaned and erroneous data removed. Three lung-deposited SA samples and one CO sample were lost due to the incorrect operation of the instruments. These control measures ensure the reliability of the retained samples. A matrix was generated from the survey responses and recoded for subsequent statistical analysis. A list of these variables is presented in the SI Table S2. All pollutant measurements and continuous variables were log-transformed and added to the matrix, for simple and multivariate regression analysis. All statistical analysis was conducted in R (version 2.10.1, R Foundation for Statistical Computing), while graphics were created using SigmaPlot (version 11.0, Systat Software, Inc.).
with only a shelf or 2 on which a few cooking utensils or materials to aid ignition sat. Roofs were either thatched or constructed from cement or plastic and leaves; gaps and holes within the roofs facilitated ventilation. None of the households had electricity; interiors were therefore dark, except for a few beams of light that were able to penetrate through the cracks and holes in the walls and roofs. A map of the general area, mean temperature, and rainfall, and photos typifying the surrounding environment and cookstove setting are presented in the Supporting Information (SI) Figures S1−S4. Study Design. Measurements were collected over 18 nonconsecutive days, between 9:00 in the morning and 7:00 in the evening between June and August, 2012. The experimental test plan is presented in Table 1. All indoor measurements were made 1 m vertically and horizontally from the cookstove (position L2), representing the pollutant environment of the woman who was cooking while ensuring the instruments were not exposed to overly high temperatures. All tests included an indoor and outdoor measurement prior to lighting the cookstove so that a baseline could be established. Start-up and steady-state modes were also distinguished. Several methods to extinguish the cookstove were observed, as this may affect the decay-rate of indoor pollutant concentrations and subsequent exposure of the women and children within the vicinity of the cookstove. All measurement times were logged on an Emissions Log Form, and several time−activity diaries were constructed for the duration of the cookstove run. Household and fuel characteristics were also collected during each test, primarily through observation by a member of the field team, but in some cases by the participant, generally the mother. These forms are provided in the SI (Figure S5 and Table S2). Emission Measurements. The lung-deposited SA concentration of particles (μm2cm−3) between 0.01 and 1 μm in size and depositing in the tracheobronchial (TB) region of the lung was measured using an AeroTrak 9000 (TSI Inc., Shoreview, MN). The AeroTrak charges particles via diffusion, and a voltage trap ensures that only the fraction of particles that would deposit in the lung, according to the International Commission on Radiological Protection (ICRP) deposition curves, pass through to the electrometer for final measurement. Mass (PM2.5) particle concentrations (μg m−3) were measured using a DustTrak 8532, also from TSI. This instrument uses the principles of light scattering in which the amount of light scattered is detected by a photodetector and the subsequent voltage is linearly proportional to the mass concentration. Finally, the Lascar EL-USB-CO sensor (Lascar Electronics) was used to measure carbon monoxide (CO). This sensor uses electrochemical sensing technology to oxidize and convert the CO gas that has diffused into the sensor into an electric current that is linearly proportional to the gas concentration. A laptop controls the start and end times. All instruments were lightweight, easily portable and provided real-time highresolution data. Additional information may be found in the SI and in previously published work.25−27 All instruments were new purchases and recently calibrated; these calibrations were verified before and after the measurement campaign. All startup and zero-calibration operations were performed every morning prior to use, and each instrument was cleaned daily, according to protocol, following the completion of the day’s measurements. Data Analysis. Instruments were synchronized every morning before heading to the field, according to the time
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RESULTS AND DISCUSSION Household and Fuel Descriptives. Measurements were collected for a total of 54 households; of these, 51 used traditional cookstoves while 3 used some type of improved cookstove. Five households possessed functioning chimneys, and four of these belonged to traditional cookstoves. The dimensions of the rooms in which the cookstoves operated were measured crudely and ranged from 8 to 250 m3, with a mean of 59 m3. Some 21 households had no windows per se, although the majority of households had numerous holes in both the walls and roofs, which made it difficult to construct a separate ventilation variable, discussed later. Most households had between 1 and 2 windows; only 6 had more than 2 windows. Windows were without glass or shutters and thus permanently open. The majority of households possessed thatched roofs (N = 37). Because these roofs cannot be completely sealed they are sloped to a specific angle to prevent rainwater from entering, which at the same time offers additional ventilation; the remaining roofs were constructed from either cement (6) or plastic and leaves (7). Roof-type tended to be similar within villages. Tobacco smoking occurred 6 times during measurement collection, always by males. Of the 54 households, 35 burned only biomass, while 19 burned a mixture of biomass and dung. The different types of biomass included logs, sticks, twigs, corn stalks, hay and straw, and the vast majority of households (N = 47) dried the biomass prior to burning it. Dung was frequently soaked in kerosene before being burned, and 55% of households also added kerosene to enhance ignition. In addition, small amounts of paper, plastic and fabric were also burned, most frequently as kindling. The amount of fuel used during each session ranged from 0.25 to 5 kg. However, these estimates are crude and may be more indicative of the amount available to burn rather than the actual amount burned. This variable was hence recoded for regression analysis as low, moderate, or high. While outdoor temperatures hovered around 32 °C during the course of the measurement campaign, rain patterns changed as the Monsoon season moved in, discussed in more detail in the Simple and Multiple Regression Analysis section. Finally, only 14 households cooked food (roti, chapati, and some different vegetables) while the majority boiled water for tea, principally in metal pots but sometimes clay; a lid was almost never used (
