Article pubs.acs.org/est
Emission Characteristics of Particulate Matter and Volatile Organic Compounds in Cow Dung Combustion Duckshin Park,† Mona L. Barabad,†,‡ Gwangjae Lee,§ Soon-Bark Kwon,† Youngmin Cho,† Duckhee Lee,† KiChul Cho,∥ and Kiyoung Lee*,⊥ †
Eco-Transport Research Division, Korea Railroad Research Institute, Uiwang-si, Gyeonggi-do 437-757, Republic of Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 305-350, Republic of Korea § Center for Environment, Health and Welfare Research, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea ∥ Department of Bio and Environmental Science, Dongnam Health College, Suwon-si, Gyeonggi-do 440-714, Republic of Korea ⊥ Department of Environmental Health and Institute of Health and Environment, Graduate School of Public Health, Seoul National University, 1 Gwanak-ro, 1 Gwanak-gu, Seoul 151-742, Republic of Korea ‡
ABSTRACT: Biomass fuel is used for cooking and heating, especially in developing countries. Combustion of biomass fuel can generate high levels of indoor air pollutants, including particulate matter (PM) and volatile organic compounds (VOCs). This study characterized PM and VOC emissions from cow dung combustion in a controlled experiment. Dung from grass-fed cows was dried and combusted using a dual-cone calorimeter. Heat fluxes of 10, 25, and 50 kW/m2 were applied. The concentrations of PM and VOCs were determined using a dust spectrometer and gas chromatography/mass spectrometry, respectively. PM and VOC emission factors were much higher for the lower heat flux, implying a fire ignition stage. When the heat flux was 50 kW/m2, the CO2 emission factor was highest and the PM and VOC emission factors were lowest. Particle concentrations were highest in the 0.23−0.3 μm size range at heat fluxes of 25 and 50 kW/m2. Various toxic VOCs, including acetone, methyl ethyl ketone, benzene, and toluene, were detected at high concentrations. Although PM and VOC emission factors at 50 kW/m2 were lower, they were high enough to cause extremely high indoor air pollution. The characteristics of PM and VOC emissions from cow dung combustion indicated potential health effects of indoor air pollution in developing countries.
1. INTRODUCTION Biomass fuel is one of the most common cooking and heating fuels in the world. More than 50% of those living in developing countries rely on biomass fuel.1 Biomass fuels account for as much as 95% of domestic energy consumption in some lowincome countries.2 The major sources of domestic biomass fuels are wood, dung, and crop residue. Biomass fuel combustion is the most important source of black carbon in the South Asia region, and such emissions can influence regional climate change.3 Because biomass fuels are often burnt in traditional open stoves without a proper ventilation system,4 biomass fuel combustion is associated with high levels of indoor air pollution.5,6 Cow dung is widely used as a domestic fuel in developing countries because it is easily obtained and possesses a high heating value. Indoor air pollution from biomass fuel combustion is one of the most important sources of ill health in developing countries. Indoor air pollution from solid fuel use was responsible for the direct premature death of 3.5 million people in 2010, especially in developing countries.7 Indoor air pollution in developing © 2013 American Chemical Society
countries has increased the risk of chronic obstructive pulmonary disease, acute respiratory infections, low birth weight, infant and perinatal mortality, pulmonary tuberculosis, nasopharyngeal and laryngeal cancer, cataracts, and lung cancer.5 Pollution from biomass burning has been found to negatively influence human health and plant productivity because of enhanced ozone and aerosol concentrations.8 Biomass burning can release a significant amount of various air pollutants. Air pollutants emitted from biomass burning include both particulate matter (PM) and gaseous compounds, such as carbon monoxide, formaldehyde, acrolein, benzene, toluene, nitrogen dioxide, and ozone.6,9−12 The particle size distribution from solid fuel combustion peaks in the accumulation mode of 0.75−2.23 μm.13 The size distribution of biomass fuels was unimodal, with a mass median Received: Revised: Accepted: Published: 12952
July 9, 2013 October 14, 2013 October 21, 2013 October 21, 2013 dx.doi.org/10.1021/es402822e | Environ. Sci. Technol. 2013, 47, 12952−12957
Environmental Science & Technology
Article
aerodynamic diameter range of 0.42−1.31 μm.14 Increased burn rates of biomass fuels were associated with higher emission rates of PM2.5, with a larger organic carbon content.14 Very high concentrations of total suspended particulates (TSPs) with elevated concentrations of toxic elements of cadmium (Cd), arsenic (As), and lead (Pb) have been measured during yak dung combustion.15 The high PM emission factors for cow dung combustion suggested significant indoor air pollution in a residential environment. Among the various biofuels that have been studied, animal dung emits the highest level of respirable particles.5 Dung cake combustion generates more PM and CO than wood burning.16 Smoke from cow dung combustion has caused histopathological changes in the lung tissues of rats.17 Fine particles emitted from the burning of dung cake are highly oxidative because of the redox active metals that they contain.18 Such high emission factors and the potential toxicity of cow dung combustion products suggests that the use of ventilation systems is needed. In addition to PM, the combustion of biofuel generates atmospheric pollutants, such as NOx, SO2, respirable PM, formaldehyde, and benzene.9 Animal dung combustion generates much more PM, CO, and cancer-causing benzene than the combustion of other fuels.10,19 Characterizing emission factors for air pollutants generated by cow dung combustion is important for better exposure assessment. The purpose of this study was to determine the size distributions of PM and the specific volatile organic compounds (VOCs) emitted from cow dung combustion. This study characterized the emission of fine particles and VOCs from cow dung combustion in controlled experiments.
kW/m2), smoke production rate (SPR, m2/s), CO and CO2 concentrations (%), oxygen consumption rate (OCR, g/s), mass change, time to ignition (TTI), time to flameout (TTF), and total heat release rate (THR, mJ/m2). The radiating electric heater of the cone calorimeter was designed to emit radiation heat of up to 100 kW/m 2 horizontally and vertically. In this study, the radiation strength of the electric heater was set at 15, 25, and 50 kW/m2. The cone calorimeter was designed for an experiment to simulate fire. It met the European Union (EU) train carrier fire protection standard (EN 45545-2) for a designated heat strength of 50 kW/m2 for fire simulations in wall or ceiling materials and 25 kW/m2 for fire simulations in floor materials. A heat strength of 15 kW/m2 was added to evaluate the emission characteristics at low combustion temperatures, such as the ignition period. According to ISO 5660-1, the combustion temperatures were estimated to be 459, 560, and 735 °C when the radiation strengths were 15, 25, and 50 kW/ m2, respectively. The dimension of the sample holder was 100 mm (W) × 100 mm (L) × 36 mm (T). The distance between the sample and heat-generating plate was set at 25 mm, and the exhaust fan capacity was fixed at 24 L/s. Before the test, N2, CO, and CO2 were calibrated using standard gases and O2 was calibrated using air. The scale and smoke detector were calibrated before the test. During the test, the gas flow rate and concentration were continuously monitored to maintain the initial conditions. The dung of five grass-fed cows was mixed and dried at room temperature in the laboratory before testing. Because the cow dung specimens were typically larger than the sample holder, they were cut into small pieces. Each piece was about 1 g, and one sample holder held about 65−70 pieces of dried cow dung. To measure the size distribution of fine particles discharged during the combustion of cow dung, a dust spectrometer (1.108; Grimm, Ainring, Germany) with a 16-channel decomposition capacity was used. The flow rate of the spectrometer was 1.6 L/min. The sampling inlet of the monitor was placed inside the duct of the cone calorimeter. The measurement was adjusted by the weight of dust collected inside the spectrometer. A 6-L silicon canister (Restek Co., Bellefonte, PA) with an internal surface and valve coated with inert silica to prevent the adsorption of VOCs was used to collect air samples while controlling the flow rate. The sampling inlet was aligned with a dust spectrometer. VOC sampling was conducted for 1 min during combustion experiments. The collected samples were preconcentrated in the lab and analyzed with a gas chromatograph/mass selective detector (GC/MSD). The GC/MSD system determined 57 chemicals designated by the United States Environmental Protection Agency (U.S. EPA) as key substances for the consideration of toxicity because of their potential carcinogenic and mutagenic properties.20 Emission factors (EFs) for PM and VOCs during cow dung combustion were determined on the basis of the measurement of flue gas volume and the mass concentration of pollutants using eq 1. EFs were expressed in milligrams of pollutants per kilogram of dried combusted cow dung.
2. METHODS This study used a dual-cone calorimeter (Fire Testing Technology, East Grinstead, West Sussex, U.K.) to observe the generation of PM and VOCs from cow dung samples at various combustion temperatures. Figure 1 shows a schematic
Figure 1. Schematic diagram of the cow dung experimental system.
diagram of the experimental system. The cone calorimeter consisted of a cone-shaped radiating electric heater, oxygen analyzer, exhaust system, mass meter to measure the sample mass, sample holder, spark ignition circuit, heat flux meter, burner to measure the methane heat release rate, a data acquisition and analysis system, and a non-dispersive infrared detector (NDIR) analyzer to measure carbon monoxide (CO) and carbon dioxide (CO2). The built-in analyzer of the cone calorimeter was used to measure the heat release rate (HRR, 12953
dx.doi.org/10.1021/es402822e | Environ. Sci. Technol. 2013, 47, 12952−12957
Environmental Science & Technology
Article
Table 1. Experimental Results for the Combustion of Cow Dung Samples 15 kW/m2 mass (g)
initial loss remaining time (s) ignition flameout heat (kW/m2) THR peak HRR CO2 emission factor (mg/dry kg) CO emission factor (mg/dry kg)
67.4 47.7 19.7 110 185 139.9 117.3 638.0 81.5
± ± ± ± ± ± ± ± ±
25 kW/m2
3.5 3.5 0.0 14 19 23.7 30.2 77.8 4.9
64.3 44.9 19.4 30 224 79.9 131.7 1297.3 80.7
± ± ± ± ± ± ± ± ±
50 kW/m2
1.8 0.2 2.0 13 130 25.0 8.1 756.5 8.7
70.1 54.4 15.7 8 1089 113.4 156.3 1407.7 41.3
± ± ± ± ± ± ± ± ±
3.2 3.3 0.9 2 220 32.8 8.0 138.2 7.0
EF (mg/kg) = concentration of pollutants (mg/m 3) × flow rate (m 3/min) × sampling time (min) /weight of burned cow dung (kg)
(1)
Concentrations of pollutants were determined using a dust spectrometer for PM and GC/MSD for VOCs. The flow rate, total sampling time, and weight of burnt material were recorded automatically by the cone calorimeter. The combustion experiments were repeated 3 times for each heat flux. SPSS version 13.0 (SPSS, Inc., Chicago, IL) was used to statistically analyze the data.
Figure 2. PM concentrations and size distributions for three different heat fluxes.
PM10 emission factors decreased as the heat flux increased, as shown in Table 2. The PM10 emission factor was 3476.5 ±
3. RESULTS Table 1 presents the results of cow dung combustion experiments. The average initial weights of the dried cow dung used in the three replicate tests were 67.4 ± 3.5, 64.3 ± 1.8, and 70.1 ± 3.2 g at heat fluxes of 15, 25, and 50 kW/m2, respectively. The weights after combustion at 15, 25, and 50 kW/m2 changed by 47.7 ± 3.5, 44.9 ± 0.2, and 54.4 ± 3.3 g, respectively. The ignition time was 110 ± 14 s at 15 kW/m2. The ignition times decreased substantially when the radiation from the electric heater was increased. The ignition and flameout times were inversely proportionally correlated with the coefficient of −0.695. The maximum heat generation (peak HRR) was 117.3 kW/m2 and gradually rose as the heater temperature increased to reach 156.3 kW/m2 at 50 kW/m2. The CO2 emission factor was 0.638 g/kg at 15 kW/m2, which increased as the heater temperature rose, as shown in Table 1. The CO2 emission factor at 50 kW/m2 was more than twice the CO2 emission factor at 15 kW/m2. The CO emission factor (mg/kg) was lowest at the highest heater temperature, indicating that the sample combustion efficiency became higher as the heater temperature increased. The particle size distribution was different for the different heat fluxes, as shown in Figure 2. When the heat flux was 15 kW/m2, 36.9% of the particles generated were sized between 3 and 4 μm. Particles of between 2 and 5 μm comprised about 62% of the total PM10 mass concentration at 15 kW/m2. When the heat flux was 25 kW/m2, particles smaller than 0.5 μm comprised 86% of the PM10 concentration. Particles between 0.23 and 0.3 μm comprised 35% of the PM10 concentration at a heat flux of 25 kW/m2. At 25 kW/m2, no particles greater than 4 μm were detected. At 50 kW/m2, the PM size distribution was substantially different. At a heat flux of 50 kW/m2, particles between 0.23 and 0.3 μm comprised 50% of the PM10 concentration and about 90% of the PM10 was smaller than 0.5 μm.
Table 2. PM Emission Factors (mg/kg) at Different Heat Fluxes emission factor (mg/kg) PM size (μm) 0.23−0.30 0.30−0.40 0.40−0.50 0.50−0.65 0.65−0.80 0.80−1.0 1.0−1.6 1.6−2.0 2.0−3.0 3.0−4.0 4.0−5.0 5.0−7.5 7.5−10.0 total
15 kW/m2 31.7 62.2 50.6 79.9 62.7 104.2 442.7 474.1 449.4 1283.4 430.7 4.5 0.4 3476.5
± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.7 13.6 8.8 20.7 10.3 6.0 93.9 167.5 207.7 739.4 322.8 2.8 0.3 1594.5
25 kW/m2 ± 69.9 ± 34.4 ± 20.4 ± 30.9 ± 9.1 ± 3.4 ± 1.2 ± 0.4 ± 0.2 0.0 0.0 0.0 0.0 589.1 ± 169.9
207.8 174.0 126.4 59.3 13.7 4.9 1.8 0.7 0.2
50 kW/m2 21.8 14.6 2.2 1.1 0.4 0.2 0.3 0.2 0.8 0.5 0.4 0.4 0.1 43.2
± ± ± ± ± ± ± ± ± ± ± ± ± ±
5.5 2.9 2.2 1.0 0.2 0.1 0.1 0.0 0.2 0.2 0.1 0.4 0.1 12.9
1594.5 mg/kg at 15 kW/m2. The PM10 emission factors at 25 and 50 kW/m2 were substantially lower at 589.1 ± 169.9 and 43.2 ± 12.9 mg/kg, respectively. The PM10 emission factor at 50 kW/m2 was only 1.2% of the value at 15 kW/m2. The highest emission factor at 15 kW/m2 was for the 3.0−4.0 μm particle size fraction. The emission factor was substantially reduced for particle sizes greater than 5 μm. When the heat flux was 25 kW/m2, the emission factor for the 3.0−4.0 μm particle size fraction was reduced to 0 mg/kg. The highest emission factors at 25 and 50 kW/m2 were for the 0.23−0.30 μm particle size fraction. While the PM1.0/PM10 ratio at 15 kW/m2 was 0.1, the PM1.0/PM10 ratios at 25 and 50 kW/m2 were 0.99 and 0.94, 12954
dx.doi.org/10.1021/es402822e | Environ. Sci. Technol. 2013, 47, 12952−12957
Environmental Science & Technology
Article
Table 3. Average VOC Concentrations (μg/m2) and the Emission Factor (mg/kg) During Cow Dung Combustion concentration (μg/m2) heat flux (kW/m )
15
25
methylchloride 1,3-butadiene methyl bromide ethylchloride acetone isopropyl alcohol 1,1-dichloroethene dichloromethane carbondisulfide trans-1,2-dichloroethylene methyl-tert-butyl-ether vinyl acetate methyl ethyl ketone cis-1,2-dichloroethylene ethylacetate hexane benzene cyclohexane bromodichloromethane heptane cis-1,3-dichloropropene methyl isobutylketone 1,1,2-trichloroethane toluene 1,2-dibromoethane tetrachloroethylene chlorobenzene ethylbenzene m,p-xylene styrene o-xylene 4-ethyltoluene 1,3,5-trimethylbenzene 1,2,4-trimethylbenzene benzyl chlororide 1,4-dichlorobenzene 1,3-dichlorobenzene 1,2-dichlorobenzene 1,2,4-trichlorobenzene
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
66.8 ± 52.9 322.4 ± 69.8 19.9 ± 17.3 3.0 ± 5.2 3432.5 ± 57.6 53.2 ± 2.0 29.6 ± 1.6 2.9 ± 2.9 24.4 ± 0.3 7.8 ± 0.3 2.9 ± 0.4 1025.6 ± 41.1 1062.9 ± 46.2 9.5 ± 0.3 12.7 ± 0.4 175.0 ± 3.2 840.4 ± 14.7 31.0 ± 0.1 51.5 ± 1.9 229.8 ± 144.1 34.5 ± 1.1 37.7 ± 1.9 48.4 ± 0.6 1369.0 ± 11.7 25.0 ± 21.6 16.2 ± 0.6 20.6 ± 0.4 189.1 ± 3.8 255.6 ± 5.4 362.2 ± 6.5 124.5 ± 2.2 42.9 ± 7.1 29.6 ± 0.3 61.9 ± 1.5 81.0 ± 6.0 ND ND ND ND
2
a
270.2 276.3 28.8 6.0 3357.1 27.1 1.7 4.8 28.8 6.1 3.0 541.8 1113.4 11.4 23.0 164.2 738.8 29.1 35.4 144.0 31.3 47.3 43.1 1170.8 37.7 15.9 20.2 159.5 209.6 281.3 100.8 35.7 27.2 51.0 83.5 22.4 7.9 33.3 56.0
76.1 64.8 1.4 5.8 234.1 0.8 0.0 0.7 1.5 0.3 0.4 67.9 33.3 0.7 3.3 8.4 22.6 1.5 0.8 5.4 2.3 2.2 0.8 17.7 0.1 0.6 0.3 1.4 2.6 5.0 0.8 0.2 0.2 1.4 7.3 19.4 6.8 28.9 48.5
emission factor (mg/kg) 50
15 a
ND 210.8 ± 5.7 ND ND 682.2 ± 10.8 35.4 ± 0.0 2.8 ± 1.0 10.0 ± 0.4 7.7 ± 0.1 0.5 ± 0.9 3.4 ± 0.2 199.3 ± 1.6 152.3 ± 3.5 2.6 ± 2.2 14.5 ± 3.4 19.6 ± 0.5 380.5 ± 2.8 7.2 ± 0.1 6.3 ± 0.2 47.4 ± 0.7 22.7 ± 0.2 13.1 ± 0.3 16.6 ± 0.8 298.7 ± 8.2 ND 16.4 ± 0.7 14.3 ± 0.2 48.2 ± 0.2 67.5 ± 0.3 103.4 ± 0.9 32.9 ± 0.3 27.1 ± 0.3 21.2 ± 1.9 27.3 ± 0.0 66.3 ± 1.7 ND ND ND ND
114.3 116.9 12.2 2.5 1420.1 11.5 0.7 2.0 12.2 2.6 1.3 229.2 471.0 4.8 9.7 69.5 312.5 12.3 15.0 60.9 13.2 20.0 18.2 495.3 15.9 6.7 8.6 67.5 88.7 119.0 42.7 15.1 11.5 21.6 35.3 9.5 3.3 14.1 23.7
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
25 32.2 27.4 0.6 2.5 99.0 0.4 0.0 0.3 0.6 0.1 0.2 28.7 14.1 0.3 1.4 3.6 9.5 0.6 0.3 2.3 1.0 0.9 0.3 7.5 0.0 0.3 0.1 0.6 1.1 2.1 0.3 0.1 0.1 0.6 3.1 8.2 2.9 12.2 20.5
29.6 ± 143.0 ± 8.8 ± 1.3 ± 1522.0 ± 23.6 ± 13.1 ± 1.3 ± 10.8 ± 3.5 ± 1.3 ± 454.8 ± 471.3 ± 4.2 ± 5.6 ± 77.6 ± 372.6 ± 13.7 ± 22.8 ± 101.9 ± 15.3 ± 16.7 ± 21.5 ± 607.0 ± 11.1 ± 7.2 ± 9.2 ± 83.8 ± 113.3 ± 160.6 ± 55.2 ± 19.0 ± 13.1 ± 27.5 ± 35.9 ± NA NA NA NA
50 23.4 30.9 7.6 2.3 25.5 0.9 0.7 1.3 0.1 0.1 0.2 18.2 20.5 0.2 0.2 1.4 6.5 0.1 0.8 63.9 0.5 0.8 0.3 5.2 9.6 0.3 0.2 1.7 2.4 2.9 1.0 3.2 0.1 0.7 2.7
NA 85.7 ± NA NA 277.5 ± 14.4 ± 1.1 ± 4.1 ± 3.1 ± 0.2 ± 1.4 ± 81.1 ± 61.9 ± 1.0 ± 5.9 ± 8.0 ± 154.8 ± 2.9 ± 2.6 ± 19.3 ± 9.2 ± 5.3 ± 6.7 ± 121.5 ± NA 6.7 ± 5.8 ± 19.6 ± 27.5 ± 42.1 ± 13.4 ± 11.0 ± 8.6 ± 11.1 ± 27.0 ± NA NA NA NA
2.3
4.4 0.0 0.4 0.1 0.0 0.3 0.1 0.7 1.4 0.9 1.4 0.2 1.1 0.0 0.1 0.3 0.1 0.1 0.3 3.3 0.3 0.1 0.1 0.1 0.4 0.1 0.1 0.8 0.0 0.7
ND = not detected (i.e.,
