Environ. Sci. Technol. 2008, 42, 2503–2508
Particle and Gas Emissions from a Simulated Coal-Burning Household Fire Pit L I N W E I T I A N , † D O N A L D L U C A S , * ,‡ SUSAN L. FISCHER,† S. C. LEE,§ S. KATHARINE HAMMOND,† AND C A T H E R I N E P . K O S H L A N D †,4 School of Public Health, Lawrence Berkeley National Laboratory, and Energy and Resources Group, University of California, Berkeley, Berkeley, California 94720, and The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Received July 5, 2007. Revised manuscript received November 16, 2007. Accepted January 7, 2008.
An open fire was assembled with firebricks to simulate the household fire pit used in rural China, and 15 different coals from this area were burned to measure the gaseous and particulate emissions. Particle size distribution was studied with a microorifice uniform-deposit impactor (MOUDI). Over 90% of the particulate mass was attributed to sub-micrometer particles. The carbon balance method was used to calculate the emission factors. Emission factors for four pollutants (particulate matter, CO2, total hydrocarbons, and NOx) were 2–4 times higher for bituminous coals than for anthracites. In past inventories of carbonaceous emissions used for climate modeling, these two types of coal were not treated separately. The dramatic emission factor difference between the two types of coal warrants attention in the future development of emission inventories.
Introduction Coal burning is a major source of the greenhouse gases (GHG) and airborne particulate matter (PM). China leads the world in coal production and consumption. Coal is the dominant energy source in China, accounting for 75 and 69% of its energy production and consumption (by calorific value calculations), respectively, in 2002 (1), and the predominance of coal in the China energy structure is not expected to change significantly within the next few decades. A sizable fraction of the coal in China is consumed in small household combustion devices. In 2002, the residential coal consumption per capita was 59.4 kg, accounting for 5.6% of the total coal consumption (1066.9 kg/capita) (1). Household coal use in urban areas of China has decreased due to policies that substitute gas and other, cleaner burning fuels, but in rural areas household coal use seems to be increasing to relieve the pressure on biomass resources (2). Emission factors of greenhouse gases and PM from coal used in household stoves are different from those used in * Corresponding author phone: 510-486-7002; fax: 510-486-7303; e-mail:
[email protected]. † School of Public Health, University of California, Berkeley. ‡ Lawrence Berkeley National Laboratory, University of California, Berkeley. § The Hong Kong Polytechnic University. 4 Energy and Resources Group, University of California, Berkeley. 10.1021/es0716610 CCC: $40.75
Published on Web 02/21/2008
2008 American Chemical Society
industrial combustion, since the combustion temperature is lower and pollution control measures are generally absent in small stove combustion devices. Zhang et al. (3) systematically measured emissions from 28 fuel/stove combinations in China, a large fraction of the combinations in use worldwide, to provide the first database for emissions from this type of combustion. In their work, coal stoves included brick and metal stoves with and without flues. Not included was a “fire pit” (“Huo Tang” in Chinese), a household combustion device long used in provincial areas of China, especially the southwest. A primitive fire pit is composed of three stones in a pit in the living room. Figure 1 shows a 0.6 m × 0.6 m fire pit in the floor of the family residence’s main room in Xuan Wei, China. In the center of the pit, four to six bricks are arranged to surround the pile of wood or coal. Between the bricks are open slots that allow air in and ash out. A tripod is used to support the cooking pot. Here we present emissions from burning 15 different fuels in a laboratory system designed to mimic the fire pits used in Xuan Wei County, China. In addition, Xuan Wei County has been the focus of many studies linking high lung cancer rates with indoor coal burning in fire pits. The lung cancer mortality rate for women in this county is China’s highest, and the men’s is among China’s highest (4). Within this county, the lung cancer rates vary by 2 orders of magnitude among different communes that use different fuels. Epidemiological studies revealed a closer association of lung cancer with the indoor burning of bituminous coal (as opposed to anthracite or wood) than with tobacco use or occupation (5–7). The gas and particle emission results presented in this paper can be used to improve emission inventories for both the local air pollution and health studies in Xuan Wei and the global climate effects of household fire pits.
Experimental Procedures Simulated Fire Pit. Figure 2 shows the laboratory stove constructed to simulate the fire pit shown in Figure 1. A metal plate at the base contains the ash, and a square firebrick plate (30 cm × 30 cm × 2 cm) provides heat insulation. Four firebricks form a base with cross-grooves that allow stoking of the fire and removal of the ash, and six standing firebricks are arranged in a circle that encloses the fire. The assembly is placed on an insulating fiber mat and an electronic scale (HP-40K) to monitor the fuel mass during the burning process. Above the fire is a 2 L stainless steel pot, filled with 1.5 L of water. The pot is independently supported so that the mass losses due to fuel combustion and water vaporization can be measured separately. Fuel Preparation. Figure 3 shows the different types of fuels burned. As obtained from local mines in Xuan Wei County, the bituminous coals are chunks approximately 10 cm in diameter. Before burning, they are broken into 2–5 cm diameter lumps. The anthracites are mostly powder and are made into briquettes in a method similar to that used in Xuan Wei. The coal powder is mixed with yellow clay purchased from a local art store in a 4:1 by mass ratio. The coal and clay are mixed with water and formed into a cylindrical pie-shaped mass ∼20 cm in diameter and ∼3 cm in height. The mixture is dried in an oven at 150 °C for about 3 h and then broken into 2–5 cm diameter lumps. Besides the 15 coal samples, one oven-dried pine wood sample, collected from a household in the research area, was also burned. The kindling used to start the coal and wood fires was Fatwood StarterStix. The composition data for the 15 coals (8), categorized by coal rank, are given in the Supporting VOL. 42, NO. 7, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
2503
FIGURE 1. The fire pit used in Xuan Wei, China
FIGURE 2. Simulated fire pit in the laboratory. Information (Table 2). No composition data are available for either the pine wood sample or the kindling. Fume Hood. The stove assembly is placed in a chemical fume hood (Figure 4) with a 26 cm diameter duct fitted with a manual damper. The draft flow, calculated from the crosssectional area and velocity measured by a hot-wire anemometer at multiple locations in the duct, is maintained at 6.4 m3/min. This flow rate was chosen to meet two constraints: high enough for the hood to contain all the emissions without visible spillage of the smoke but low enough to not disturb the fire. The front glass panels of the hood were removed to further reduce the air velocity at the fire. The resulting air velocity at the front surface of the hood is 0.1 m/s, lower than that of typical air currents (0.25 m/s) in a closed room (9, 10). Burn Cycle. The coal fire requires about 15 min to light. First, three to five pieces of kindling wood (∼50 g) are lit by a propane torch. After 2 min, when the kindling is burning well, ∼100 g of additional kindling is added. The kindling is piled to fill the stove to the highest level possible with a limited amount of wood. Between 5 and 8 min, when some wood embers have built up in the bottom layer of the wood pile, about 500 g of coal are gradually added to the fire. If the coal is difficult to light, 30 g of kindling are reserved and added at minute 8. The coal is also divided, with 100 g reserved and added with the reserved kindling. At minute 12, when most of the kindling has burned and the bottom bed of the coal has been lit, the water pot is placed above the fire. The fire is not disturbed until about minute 20; at this point, more coal is added if the fire does not appear sustainable. If coal lumps become plastic and congeal into a large piece, an event that blocks the air flow and tends to extinguish the fire, the fire is stoked and poked. 2504
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 7, 2008
The experimental cycle involves heating 1.5 kg of water from ambient temperature to boiling and then simmering for 10 min. Water is brought to boil as rapidly as possible during the heating phase and is then maintained within 5 °C of boiling during the simmering phase. These phases take 20-60 min, so the entire process takes 30–70 min depending on the fuel type. After the experiment, the remaining ash is weighed. The burn cycle is similar in time and scale as in the households of Xuan Wei, where lighting a fire and cooking a meal usually takes 1–1.5 h. The fire can smolder for another hour if left alone. In the field, the fire is allowed to die or it is maintained until the next meal is cooked. In the laboratory, the fire is extinguished by a water spray after each experiment. Because each type of coal burned differently, it was difficult at first to obtain repeatable results. Many coal fires were studied to determine how best to obtain consistent results; only results from fires that were considered “normal” are presented here. Gas and Particulate Matter Monitoring. The apparatus for monitoring gases and particles is illustrated in Figure 4. Total hydrocarbons (THC), oxygen (O2), nitrogen oxides (NOx), carbon monoxide (CO), and carbon dioxide (CO2) are measured each minute with a Horiba online gas-analyzer system (FMA-220, CLA-220, AIA-210, and AIA-220). The system is calibrated and zeroed daily. Particulate matter (PM) is monitored continuously with a MIE personal DataRAM 1200 particulate monitor; the instrument is set to measure PM2.5 in the 0.001–400 mg/m3 range (11). The instrument is calibrated by comparing the recorded time-weighted average (TWA) with the TWA measured gravimetrically on a filter downstream from the optical chamber. Size-Segregated Particle Sample Collection. Isokinetic air samples are also drawn from an 18 mm diameter thinwall probe. A microorifice uniform deposit impactor (MOUDI Model 110, MSP Corp.), operating at a flow rate of 30 L/min, is used to collect size-fractionated samples on polycarbonate filters (FPC4537 filter, Zefon International). The filter samples are measured gravimetrically and examined with scanning electron microscopes. The impactor has 50% cut-point aerodynamic diameters of 10, 5.6, 3.2, 1.8, 1.0, 0.56, 0.32, 0.18, 0.1, and 0.056 µm on stages one through ten, respectively. A 37 mm Teflon filter is used as the after-filter. Flow rate and stagnation pressure are continuously monitored. To prevent overloading the filters, particle samples are collected for 30 s every 3 min during the burn cycle. Airborne Particle Sample Collection. Airborne particle samples are collected with various filter media for different analytic techniques. Teflon membrane filters are used for mass weighing and elemental analysis, silver membrane filters for electron microscopy studies, and Pallflex Teflon coated on glass-fiber filters for free radical and PAH analysis, and for toxicity tests. The system for collecting airborne particle samples is not isokinetic in that the inlet velocity in the probe is 5 times higher than in the duct (see Figure 4). Air is drawn from the duct through ¼ in. stainless steel sampling probes 0.5 m downstream of the duct inlet and 1 m upstream of the damper. Calculations estimate that up to 20% of particles 3–10 µm in size are lost by the probe, but the collection efficiency of particles smaller than 3 µm is not affected (12). The average stack temperature at the location of the sampling probes during the combustion experiments was 30 ( 1 °C, which is 5 °C higher than that of ambient air. Copper lines are used between sampling probe and the ports for filter sampling and gas monitoring. The mass of particulate matter on the 37 mm Teflon filters is measured with a Cahn 29 Electro Balance (sensitivity, 0.001 mg). Humidity and temperature in the weighing room were held at 35 ( 5% and 75 ( 5 °F,
FIGURE 3. Photographs of the fuels burned: (a) kindling used to light the fire; (b) pine wood from Xuan Wei, China; (c) chunks of a bituminous coal; (d) powder of an anthracite; (e) yellow clay used as a binder to make coal briquettes; (f) briquettes made from d and e.
FIGURE 4. Schematic of the experiment . respectively. All filters are equilibrated to the room temperature and humidity for at least 24 h before weighing. EC/OC Analysis. The thermal/optical reflectance (TOR) method was applied to determine organic and elemental carbon (EC/OC) (13). Quartz fiber filter samples were analyzed for OC/EC by DRI Model 2001 thermal/optical carbon analyzer. The protocol involves heating a 0.526 cm2 punch aliquot of a filter stepwise in a nonoxidizing helium (He) atmosphere to measure organic carbon, and in an oxidizing atmosphere of 2% oxygen in a balance of helium to measure elemental carbon (14).
Emission Factor Calculation. The carbon balance method (3, 15), which does not require the measurement of the duct flow rates, was applied to calculate the emission factors (EF) of particulate matter and gases. The results were comparable to those obtained by the direct method of EF calculation (8), which multiplies the average duct concentration by the air flow rate in the duct and the duration, divided by the fuel consumed. The mass balance for carbon is described as Cf - Ca ) CCO2 + CCO + CTHC + CPM, with Cf ) carbon mass in the fuel and Ca ) carbon mass in the bottom ash, including the unburned solid fuel VOL. 42, NO. 7, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
2505
FIGURE 5. Real time monitoring of three representative burn cycles of anthracite, bituminous coal, and kindling wood. or char. Rearranging and defining K as the ratio of the airborne carbon released as products of incomplete combustion to the carbon released as CO2 leads to K ) CPIC ⁄ CCO2 If the K-factor and the amount of fuel carbon consumed are determined for a burn cycle, the emission factor of CO2 per mass of fuel consumed (Mf) can be calculated as EFCO2 ) 44(Cf - Ca) ⁄ 12Mf(1 + K) Similar expressions are used for other pollutants, including NOx using its molar ratio to CO2.
Results and Discussion Characterization of Coals. Three anthracite and 12 bituminous coals from Xian Wei were tested for their moisture content, ash, volatile, and fixed carbon content and carbon, hydrogen, nitrogen, sulfur, and oxygen content (Table 2 in the Supporting Information). The bituminous coals all contained less than 0.5% sulfur, while the anthracite coals had 3–5% sulfur. According to the Chinese coal quality standards (GB/T 15224-2004), the three anthracites are classified as high-sulfur (>3%) and high-ash (>30%); the 12 bituminous coals contain extremely low levels of sulfur (2100 °C) operations such as those encountered in cyclone burners. The mass fraction of nitrogen is below 1.5% in the 15 bituminous coals measured in the current study, and the corresponding emission factor is below 4.0 g/(kg of fuel), while anthracite contains less than 0.8% nitrogen and yields less than half as much NOx as the bituminous coals. Emission Factors. The emission factors (g/kg) for anthracite and bituminous coals on a fuel mass basis are shown in Table 1. VOL. 42, NO. 7, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
2507
TABLE 1. Mean Emission Factors (g/kg) for the Two Coal Types mean emission factor (g/(kg of fuel)) pollutant emitted
anthracite coals
bituminous coals
PM CO2 CO THC NOx
2.9 ( 0.3 1751 ( 105 92.9 ( 8.7 15.5 ( 1.3 1.10 ( 0.17
11.2 ( 1.0 2269 ( 59 73.7 ( 3.7 37.0 ( 3.1 2.61 ( 0.16
The summary statistics for the anthracite coal group and bituminous coal group were determined from the means for three anthracite and 12 bituminous coals, respectively, with a minimum of three experiments for each individual coal (62 total coal experiments). A detailed table (Table 3) is presented in the Supporting Information. For coal fires, emission factors for four pollutants, all except for CO, are significantly higher from the bituminous coals than the anthracites. Bituminous coal PM emission factors (11.2 g/kg) are nearly 4 times as high as those of anthracites (2.9 g/kg). Similarly, Butcher and Ellenbecker (24) reported a PM emission factor for bituminous coal, 10.4 g/kg, which was 20 times larger than that for anthracite, 0.33–0.62 g/kg. In past inventories of carbonaceous emissions used for climate modeling, these two types of coal were not treated separately (25). The dramatic emission factor difference between the two types of coal warrants attention in the future development of emission inventories.
Acknowledgments We thank Kirk Smith for helpful discussions and Robert Chapman of the USEPA for the coals. We also thank Scott McCormick and his staff for their assistance. This work was supported by the Environmental Health Sciences Superfund Basic Research Program (Grant No. P42ESO47050-01) from the National Institute of Environmental Health Sciences, the Wood Calvert Chair in Engineering (UCB), the National Cancer Institute, and the University of California Toxics Substances Research and Training Program.
Supporting Information Available Tables on the proximate and ultimate analyses of the 15 coals and the emission factors of the pollutants from each experiment. This material is available free of charge via the Internet at http://pubs.acs.org.
Literature Cited (1) Lin X. Y. China Energy Statistics Yearbook 2000–2; China Statistics Publishing House: Beijing, 2004. (2) Smith K. R.; Tian L. W. Indoor coal smoke and cancer. In Air Pollution and Cancer; Cogliano V, Straif K, Samet J., Eds.; IARC: Lyon, France; in press. (3) Zhang, J.; Smith, K. R.; Ma, Y.; Ye, S.; Jiang, F.; Qi, W. Greenhouse gases and other airborne pollutants from household stoves in China: A database for emission factors. Atmos. Environ. 2000, 34, 4537–4549. (4) Mumford, J. L.; He, X. Z.; Chapman, R. S.; Cao, S. R.; Harris, D. B.; Li, X. M. Lung cancer and indoor Aair-pollution in XuanWei. China Sci. 1987, 235 (4785), 217–220.
2508
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 7, 2008
(5) Mumford, J. L.; Harris, D. B.; Williams, K. Indoor air sampling and mutagenicity studies of emissions from unvented coal combustion. Environ. Sci. Technol. 1987, 21, 308–311. (6) Chapman, R. S.; Mumford, J. L.; Harris, D. B.; He, Z. Z.; Jiang, W. Z.; Yang, R. D. The epidemiology of lung cancer in Xuan Wei, China: Current progress, issues, and research strategies. Arch. Environ. Health 1988, 43 (2), 180–5. (7) He X.; Yang R. Lung Cancer and Indoor Air Pollution from Coal Burning; Yunnan Science and Technology Publishing House: Kunming, China, 1994. (8) Tian L. W. Coal Combustion Emissions and Lung Cancer in Xuan Wei, China. Ph.D. dissertation, University of California, Berkeley, CA, 2005. (9) Ballard-Tremeer G. Emissions of Rural Wood-Burning Cooking Devices. Ph.D. dissertation, University of the Witwatersrand, Johannesburg, South Africa, 1997. (10) Ballard-Tremeer, G; Jawurek, H. H. The ”hood method” of measuring emissions of rural cooking devices. Biomass Bioenergy 1999, 16 (5), 341–345. (11) MIE. Instruction Manual: Personal DataRam Models pDR1000AN and pDR-1200; MIE: Bedford, MA, 2000. (12) Hinds W. C. Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles, 2nd ed.; Wiley: New York, 1999. (13) Chow, J. C.; Watson, J. G.; Chen, L. W. A.; Arnott, W. P.; Moosmiller, H. Equivalence of elemental carbon by thermal/ optical reflectance and transmittance with different temperature protocols. Environ. Sci. Technol. 2004, 38, 4414–4422. (14) Cao, J. J.; Lee, S. C.; Ho, K. F.; Zhang, X. Y.; Zou, S. C.; Fung, K. Characteristics of carbonaceous aerosol in Pearl River Delta Region, China during 2001 winter period. Atmos. Environ. 2003, 37 (11), 1451–1460. (15) Smith, K. R.; Khalil, M. A. K.; Rasmussen, R. A.; Thorneloe, S. A.; Manegdeg, F; Apte, M. Greenhouse gases from biomass and fossil-fuel stoves in developing countriessA Manila pilot study. Chemosphere 1993, 26 (1–4), 479–505. (16) Rau, J. A. Composition and size distribution of residential wood smoke particles. Aerosol Sci. Technol. 1989, 10 (1), 181–192. (17) Bond T. C. Covert D. S. Kramlich J. C. Larson T. V. Charlson R. J. Primary particle emissions from residential coal burning: Optical properties and size distributions. J. Geophys. Res., [Atmos.] 2002, 107, D21. (18) Venkataraman, C.; Rao, G. U. M. Emission factors of carbon monoxide and size-resolved aerosols from biofuel combustion. Environ. Sci. Technol. 2001, 35, 2100–2107. (19) Kleeman, M. J.; Schauer, J. J.; Cass, G. R. Size and composition distribution of fine particulate matter emitted from wood burning, meat charbroiling, and cigarettes. Environ. Sci. Technol. 1999, 33, 3516–3523. (20) Gupta, S.; Saksena, S.; Shankar, V. R.; Joshi, V. Emission factors and thermal efficiencies of cooking biofuels from five countries. Biomass Bioenergy 1998, 14 (5–6), 547–559. (21) Mitra, A.; Sarofim, A. F.; Barziv, E. The influence of coal type on the evolution of polycyclic aromatic-hydrocarbons during coal devolatilization. Aerosol Sci. Technol. 1987, 6 (3), 261–271. (22) Xian Y., Qiao J., Wang G. Personal exposure levels of air pollutants in Xuan Wei. In Lung Cancer and Indoor Air Pollution from Coal Burning; He, X., Yang, R, Eds.; Yunnan Science and Technology Publishing House: Kunming, China, 1994; pp 151–157.. (23) Sarofim A. F. Pollutant formation and destruction. In Fundamentals of the Physical-Chemistry of Pulverized Coal Combustion; Lahaye, J., Prado G., Eds.; Kluwer Academic Publishers;: Boston Hingham, MA, 1987; pp 245–268.. (24) Butcher, S. S.; Ellenbecker, M. J. Particulate emission factors for small wood and coal stoves. J. Air Pollut. Control Assoc. 1982, 32 (4), 380–384. (25) Cooke, W. F.; Liousse, C.; Cachier, H.; Feichter, J. Construction of a 1 degrees × 1 degrees fossil fuel emission data set for carbonaceous aerosol and implementation and radiative impact in the ECHAM4 model. J. Geophys. Res., [Atmos.] 1999, 104 (D18), 22137–22162.
ES0716610
