ARTICLE pubs.acs.org/est
Particle Size Distribution and Polycyclic Aromatic Hydrocarbons Emissions from Agricultural Crop Residue Burning Hefeng Zhang,†,‡ Dawei Hu,† Jianmin Chen,*,† Xingnan Ye,† Shu Xiao Wang,‡ Ji Ming Hao,*,‡ Lin Wang,†,|| Renyi Zhang,§ and Zhisheng An† †
Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China School of Environment, State Key Joint Laboratory of Environment Simulation and Pollution Control, Tsinghua University, Beijing 100084, China § Department of Atmospheric Sciences, Texas A&M University, College Station, 77843, United States Research Institute for Changing Global Environment, Fudan University, Shanghai 200433, China
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‡
bS Supporting Information ABSTRACT: Laboratory measurements were conducted to determine particle size distribution and polycyclic aromatic hydrocarbons (PAHs) emissions from the burning of rice, wheat, and corn straws, three major agricultural crop residues in China. Particle size distributions were determined by a wide-range particle spectrometer (WPS). PAHs in both the particulate and gaseous phases were simultaneously collected and analyzed by GC-MS. Particle number size distributions showed a prominent accumulation mode with peaks at 0.10, 0.15, and 0.15 μm for rice, wheat, and cornburned aerosols, respectively. PAHs emission factors of rice, wheat, and corn straws were 5.26, 1.37, and 1.74 mg kg1, respectively. It was suggested that combustion with higher efficiency was characterized by smaller particle size and lower PAHs emission factors. The total PAHs emissions from the burning of three agricultural crop residues in China were estimated to be 1.09 Gg for the year 2004.
’ INTRODUCTION Biomass burning is an important source of particulate pollutants and volatile organic compounds in the atmosphere and has a significant impact on global climate change and adverse effects on human health.14 A number of measurements have been performed to characterize the emissions of biomass burning, including field measurements,5,6 aircraft-based measurements,79 and/or laboratory studies.10,11 Burning of agricultural crop residues, including field burning and burning as domestic fuel, is a common practice of land preparation and disposal of crop wastes in China. It releases a large amount of pollutants into the atmosphere, including CO, CO2, particulate matter, hydrocarbons, and other matters, which could cause serious local and regional environmental impacts.1113 In an extreme case, it was observed that smoke emitted from field burning reduces visibility drastically and leads to the variations of cloud condensation nuclei (CCN) activation.14 In addition, smoke emitted from domestic fuel burning could cause reduced indoor air quality and contribute to acute and chronic respiratory diseases.15 Studies on particle size distributions of smoke emissions from the burning of agricultural crop residues are rather scarce. Keshtkar and Ashbaugh developed a specifically designed combustion chamber to simulate agricultural burning and examined the particle size distribution.16 Da Rocha et al. measured agricultural biomass burning in S~ao Paulo state, Brazil and r 2011 American Chemical Society
estimated the influence on aerosol size distribution and dry deposition.17 Li et al. performed a field burning experiment to estimate particle mass size distribution from open burning of wheat straw and corn straws in China.6 Stohl et al. measured particle chemical composition and size distribution during the period of agricultural fires in Eastern Europe.18 Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants. PAHs are chiefly byproducts of incomplete combustion of both fossil fuels and biomasses.19,20 A few studies on PAHs emissions from the burning of agricultural crop residues have been conducted. Dhammapala et al. measured pollutants from postharvest agricultural burning and presented emission factors of PAHs from field burning of wheat stubble.21 Keshtkar and Ashbaugh simulated agricultural waste residue burning and determined emission factors of PAHs from rice straw burning.16 Jenkins et al. developed a wind tunnel to simulate agricultural burning and measured total PAHs emissions.22,23 Because of lack of measurement data in China, current estimates of PAHs emissions from the burning of straws were given by Xu et al.24 based on the median values of PAHs emission factors (log-normally distributed), which introduced uncertainties in emission factors of PAHs. Received: December 1, 2010 Accepted: May 17, 2011 Revised: March 16, 2011 Published: May 26, 2011 5477
dx.doi.org/10.1021/es1037904 | Environ. Sci. Technol. 2011, 45, 5477–5482
Environmental Science & Technology
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Figure 1. Schematic graph of PAHs sampling system.
In this study, laboratory measurements were conducted to characterize particle size distribution and PAHs emissions from the burning of three typical agricultural crop residues in China. The measurements examined particle size distribution of fresh smoke and the evolution of the size distribution, as well as provided the possible growth mechanism of particle size in a steady-state environment. Furthermore, because of the potential adverse effects of PAHs on human health, the estimated emission factors and emission inventories of PAHs from the burning of agricultural crop residues were also evaluated.
’ METHODOLOGY Combustion Experiments and Particle Sampling. A schematic view of the particle sampling and PAHs sampling system was shown in Figure 1. Particle sampling was carried out using a self-designed combustion stove and a stainless-steel environmental aerosol chamber equipped with a set of sampling instruments, described in detail elsewhere.11 PAHs sampling system consisted of five parts: air supply system, combustion stove, PAHs sampler, flowmeter, and aerosol chamber (Figure 1). The stove was a cylinder 60 cm in diameter and 80 cm high. Air supply was controlled by an air inlet at the bottom. The volume of the aerosol chamber was 4.50 m3 with a mixing fan at the bottom. The inner temperature and relative humidity (RH) of aerosol chamber was be measured by a hygroclip monitor (model IM-4, Rotronic). A condensation particle counter (CPC) and a wide-range particle spectrometer (WPS) were connected to the aerosol chamber through a control valve. Rice, wheat, and corn straws, which account for 78% of the total yield of agricultural residues in China,25,26 were chosen as representatives of agricultural crop residues. Three agricultural crop residues were collected from the rural residential areas in China.11 Before each measurement, agricultural crop residues were dried for 24 h at 100 °C in an oven and weighed on an analytical balance (Sartorius BP211D) with a detection limit of 10 μg. About 20 g of agricultural crop residue for each test was ignited in the combustion stove. The produced smoke was introduced into the chamber immediately. After reaching the pressure equilibrium between the inside and the outside of the chamber, a “steady-state environment” was established. Then, the particle analytical instruments, such as a condensation particle counter (CPC) and a wide-range particle spectrometer (WPS), were connected to the aerosol chamber through the sampling valve. Particle sampling was conducted every 30 min. To maintain the inside-to-outside pressure equilibrium of the aerosol chamber during the sampling, the ambient
air screened by activated charcoal and HEPA filters was supplemented into the chamber. For each agricultural crop residue, five parallel burns were conducted. Before each test, levels of background particles and PAHs were measured. During the experiment periods, background temperature and RH were between 26 and 29 °C and 55 and 69%, respectively. After burning, the unburned straws and ash were collected for weighing. Particle Sampling Instrument. The particle number concentrations in the range of 0.013 μm were monitored by a CPC (model 3771, TSI Inc., USA) with a flow rate of 1 L/min. The smoke size distribution was recorded online by a WPS (model 1000XP, MSP Co., USA) with a wide size range from 10 nm to 10 μm and a sheath flow rate of 3 L/min. Before and after the observation, the WPS was calibrated with NIST PSL spheres (0.1007, 0.269, 0.701, 1.36, 1.6, and 4.0 μm mean diameter). Combustion Efficiency (CE) and Modified Combustion Efficiency (MCE). Flaming and smoldering combustion are distinguished by their different combustion efficiencies (CE), defined as the ratio of released carbon in the form of CO2 to the total mass of carbon released during combustion (CE = C[CO2]/ C[total]).27 Modified combustion efficiency (MCE) can be used if only CO2 and CO are measured (MCE = C[CO2]/(C[CO2]þ C[CO])). CE and MCE are usually close to 1 during the flaming phase. Smoldering combustion is a lower-temperature oxidation process ( 0.9).11 From Figure 3, we can conclude that the emissions from the burning of agricultural crop residues were dominated by fine particles (less than 2.5 μm), implying a significant threat to human health. Figure 4 shows the surface, volume, and mass distributions (log-normal fitting) from the burning of rice, corn, and wheat straws, respectively. The particle mass distribution was obtained by assuming a particle density of 1 g cm3. All size distributions showed a feature of unimodal spectra similarly to number size distributions. The results revealed that fresh smoke emitted from agricultural fires was characterized by unimodal distributions in the accumulation mode. Evolution of Particle Size Distribution. Figure 5 presents the evolution of particles emitted from the burning of rice, wheat, and corn straws in the “steady-state environment”. The evolution of particle number concentrations and size distributions was prominent during the aging. The initial peak number concentrations of particles emitted from the burning of rice straw, wheat straw, and corn straws were about 2.5 105, 3.4 105, and 2.0 105 particles cm3, with a median diameter of 0.10, 0.15, and 0.15 μm, respectively. After 4 h aging, the final peak number concentrations shrunk to 0.4 105, 1.1 105, and 0.4 105 particles cm3, and the corresponding particle diameters grew to 0.24, 0.23, and 0.27 μm, respectively. The decay of number concentration was obvious during the aging. However, the size distribution showed a relatively stable mode with a slight shift toward larger particle diameters. The evolution of size distribution could be explained with dilution, coagulation, growth by condensation of low-volatility gases onto the particles, or shrinkage. Emission Factors of PAHs. Emission factors of PAHs (gaseous þ particulate phase) are shown in Table 1. The average PAHs emission factors from multiple tests of rice, wheat, and corn straws were 5.26, 1.37, and 1.74 mg kg1, respectively. Jenkins et al. reported that particulate PAHs emission factors of agricultural fuels ranged from 0.12 to 4 mg kg1.22 Particulate PAHs emission factor given by Keshtkar and Ashbaugh was about 18.6 mg kg1 for rice straw.16 Dhammapala et al. concluded that PAHs emission factors for both particulate and gaseous phase was 17 ( 8.2 mg kg1 for wheat straw.21 They also indicated that PAHs emission factors for wheat stubble were higher in a chamber experiment (700 ( 100 mg kg1) than those from field burning (200 ( 200 mg kg1).33 The total PAHs emission factor for indoor straw burning was 343.3 mg kg1.34 Compared with those studies, the data in this study were much lower than most values reported above. The variation could be attributed to different combustion condition, such as combustion type (pile fire versus spreading fire), moisture content, or fuel burning amount. In this study, the three kinds of agricultural crop residues burning were dominated by flaming (MCE > 0.9),11 which might contribute to the lower emission factors of PAHs. Atmospheric Implication. The total consumption of agricultural crop residues in China was about 446 Tg during 2004, in which 24% (about 106 Tg) was burned as domestic fuel and 22% (about 100 Tg) was burned by field burning.11 The total consumption of agricultural crop residues in China was provided in our previous paper, of which about 23.7% of rice straw, 25.5% 5480
dx.doi.org/10.1021/es1037904 |Environ. Sci. Technol. 2011, 45, 5477–5482
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Table 1. Emission Factors of PAHs from Agricultural Crop Residue Burning (Units: mg kg1) rice straw (n = 5) PAHs
a
particle
corn straw (n = 5) gasa
particlea
wheat straw (n = 5) gasa
particlea
gasa
naphthalene
0.01
1.88
/
0.41
/
acenaphthylene
0.02
0.67
0.03
0.2
0.03
0.28 /
acenaphthene
0.02
0.08
0.11
0.03
0.14
0.19
fluorene
0.01
0.06
0.04
0.04
0.02
0.02
anthracene
0.33
0.40
0.17
0.06
0.09
/
phenanthrene
0.04
0.11
0.07
0.01
0.06
0.01
fluoranthene
0.27
0.09
0.17
0.01
0.14
0.02
pyrene benz [a] anthracene
0.23 0.06
0.07 0.02
0.11 0.01
0.01 0.01
0.11 /
0.01 0.01
chrysene
0.17
0.08
0.13
0.02
0.07
0.02
benzo [a] pyrene
0.10
0.04
/
/
/
/
benzo [b] fluoranthene
0.04
/
0.04
/
0.02
/
benzo [k] fluorathene
0.08
0.03
0.05
0.01
0.04
0.01
benzo [g,h,i] perylene
0.12
0.04
/
/
/
0.03
indeno [1,2,3-cd] pyrene
0.14
/
/
/
/
0.05
dibenz [a,h] anthracene ΣPAHs
0.13 1.64
0.05 3.62
/ 0.93
/ 0.81
/ 0.72
/ 0.65
Note: “/” denotes “Not detected”.
agricultural straws for the year of 2003 were about 6.53 Gg.24 Our data were lower than Xu’s results, which may be mostly attributed to the PAHs emission factors.24 The PAHs emission density in individual province and municipality in 2004 are presented in Figure 6. PAHs emission density in eastern China was much higher than that of other provinces in the west. The emission densities of Shandong, Henan, and Jiangsu ranked as the top three. It should be stressed in this study that the emission estimation of PAHs could be underestimated because it was obtained mainly based on the PAHs emission factors for the flaming conditions. However, open field burning and domestic fuel burning also include the smoldering phase, whose emission factors of PAHs are believed to be higher. Therefore, further investigations under smoldering phase are needed to evaluate the total PAHs emissions from the burning of agricultural crop residues in China.
Figure 6. Geographical distribution of PAHs emission density (area normalized) in China (units: g km2).
of wheat straw, and 50.8% of corn straw were estimated to be burned.11 According to PAHs emission factors and agricultural crop residue consumption, the PAHs emissions were estimated to be 1.09 Gg in the year 2004 (Table S1). Detailed PAHs emission information on individual province is provided in Table S1. Considering enormous differences in economic development and people’s behavior to utilize agricultural crop residues, PAHs emissions varied significantly among provinces in China. The annual PAHs emissions at provincial level ranged from 0.6 103 g in Xizang to 81 103 g in Shandong. As a typical agricultural province, Shandong contributed the largest portion of PAHs emissions in China. Henan ranked second in the PAHs emissions. Xu et al. estimated the total PAHs emissions from
’ ASSOCIATED CONTENT
bS
Supporting Information. Emissions of total, particulate, and gaseous PAHs from burned rice, wheat, and corn straws in China (Table S1). This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*Phone: þ86-21-65642521; fax: þ86-21-65642080; e-mail:
[email protected] (J.C.),
[email protected] (J.M.H).
’ ACKNOWLEDGMENT This work is supported by the National Natural Science Foundation of China (21077025, 41005061, 40875053, 41075088) 5481
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Environmental Science & Technology and Science & Technology Commission of Shanghai Municipality (10231203801, 10JC1401600, 09160707700).
’ REFERENCES (1) Levine, J. S.; Cofer, W. R.; Cahoon, D. R.; Winstead, E. L. Biomass burning: a driver for global change. Environ. Sci. Technol. 1995, 29 (3), 120A–125A. (2) Andreae, M. O.; Merlet, P. Emission of trace gases and aerosols from biomass burning. Global Biogeochem. Cycles 2001, 15 (4), 955–966. (3) Andreae, M. O. Biomass burning: Its history, use, and distribution and its impact on environmental quality and global climate. In Global Biomass Burning, Atmospheric, Climatic, and Biospheric Implications; Levine, J. S., Ed.; MIT Press: Cambridge, MA, 1991; pp 321. (4) Lighty, J. S.; Veranth, J. M.; Sarofim, A. F. Combustion aerosols: factors governing their size and composition and implications to human health. J. Air Waste Manage. Assoc. 2000, 50, 1565–1618. (5) Hays, M. D.; Fine, P. M.; Geron, C. D.; Kleeman, M. J.; Gullett, B. K. Open burning of agricultural biomass: physical and chemical properties of particle-phase emissions. Atmos. Environ. 2005, 39 (36), 6747–6764. (6) Li, X. H.; Wang, Sh. X.; Duan, L.; Hao, J. M.; et al. particulate and trace gas emissions from open burning of wheat straw and corn stover in China. Environ. Sci. Technol. 2007, 41, 6052–6058. (7) Hobbs, P. V.; Reid, J. S.; Kotchenruther, R. A.; Ferek, R. J.; Weiss, R. Direct radiative forcing by smoke from biomass burning. Science 1997, 275 (5307), 1776–1778. (8) Yan, X.; Ohara, T.; Akimoto, H. Bottom-up estimate of biomass burning in mainland China. Atmos. Environ. 2006, 40, 5262–5273. (9) Mieville, A.; Granier, C.; Liousse, C.; Guillaume, B.; Mouillot, F.; Lamarque, J. F.; Gregoire, J. M.; Petron, G. Emissions of gases and particles from biomass burning during the 20th century using satellite data and a historical reconstruction. Atmos. Environ. 2010, 44 (11), 1469–1477. (10) Burling, I. R.; Yokelson, R. J.; Griffith, D. W. T.; Johnson, T. J.; Veres, P.; Roberts, J. M.; Warneke, C.; Urbanski, S. P.; Reardon, J.; Weise, D. R.; Hao, W. M.; de Gouw, J. Laboratory measurements of trace gas emissions from biomass burning of fuel types from the southeastern and southwestern United States. Atmos. Chem. Phys. 2010, 10 (22), 11115–11130. (11) Zhang, H.; Ye, X.; Cheng, T.; Chen, J. M.; Yang, X.; Wang, L.; Zhang, R. Y. A laboratory study of africultural crop residue combustion in China: emission factors and emission inventory. Atmos. Environ. 2008, 42, 8432–8441. (12) Guo, H.; Wang, T.; Simpson, I. J.; Blake, D. R.; Yu, X. M.; Kwok, Y. H.; Li, Y. S. Source contributions to ambient VOSs and CO at a rural site in eastern China. Atmos. Environ. 2004, 38, 4551–4560. (13) Duan, F.; Liu, X.; Yu, T.; Cachier, H. Identification and estimate of biomass burning contribution to the urban aerosol organic carbon concentrations in Beijing. Atmos. Environ. 2004, 38, 1275–1282. (14) Dusek, U.; Frank, G. P.; Hildebrandt, L.; Curtius, J.; Schneider, J.; Walter, S.; Chand, D.; Drewnick, F.; Hing, S.; Jung, D.; Borrmann, S.; Andreae, M. O. Size matters more than chemistry for cloud-nucleating ability of aerosol particles. Science 2006, 312, 1375–1378. (15) Ezzati, M.; Kammen, D. M. The health impacts of exposure to indoor air pollution from solid fuels in developing countries: knowledge, gaps, and data needs. Environ. Health Perspect. 2002, 110, 1057–1068. (16) Keshtkar, H.; Ashbaugh, L. L. Size distribution of polycyclic aromatic hydrocarbon particulate emission factors from agricultural burning. Atmos. Environ. 2007, 41, 2729–2739. (17) Da Rocha, G.; Allen, A. G.; Cardoso, A. A. Influence of agricultural biomass burning on aerosol size distribution and dry deposition in Southeastern Brazil. Environ. Sci. Technol. 2005, 39, 5293–5301. (18) Stohl, A.; Berg, T.; Burkhart, J. F.; et al. Arctic smoke-record high air pollution levels in the European Arctic due to agricultural fires in Eastern Europe in spring 2006. Atmos. Chem. Phys. 2007, 7, 511–534. (19) Mastral, A. M.; Callen, M. S. A review on polycyclic aromatic hydrocarbon (PAH) emission from energy generation. Environ. Sci. Technol. 2000, 34, 3051–3057.
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(20) Pozzoli, L.; Gilardoni, S.; Perrone, M. G.; De Gennaro, G.; De Rienzo, M.; Vione, D. Polycyclic aromatic hydrocarbons in the atmosphere: Monitoring, sources, sinks and fate. I: Monitoring and sources. Ann. Chim. 2004, 94, 17–32. (21) Dhammapala, R.; Claiborn, C.; Jimenez, J.; Corkill, J.; Gullett, B.; Simpson, C.; Paulsen, M. Emission factors of PAHs, methoxyphenols, levoglucosan, elemental carbon and organic carbon from simulated wheat and Kentucky bluegrass stubble burns. Atmos. Environ. 2007, 41, 2660–2669. (22) Jenkins, B. M.; Jones, A. D.; Turn, S. Q.; Williams, R. B. Emission factors for polycyclic aromatic hydrocarbons from biomass burning. Environ. Sci. Technol. 1996, 30, 2462–2469. (23) Jenkins, B. M.; Jones, A. D.; Turn, S. Q.; Williams, R. B. Particle concentrations, gas-particle partitioning, and species intercorrelations for polycyclic aromatic hydrocarbons (PAH) emitted during biomass burning. Atmos. Environ. 1996, 30 (22), 3825–3835. (24) Xu, S. S.; Liu, W. X.; Tao, S. Emission of polycyclic aromatic hydrocarbons in China. Environ. Sci. Technol. 2006, 40, 702–708. (25) Ministry of Agriculture, P. R. C. China Agriculture Statistical Report 2004; China Agriculture Press: Beijing, China, 2005. (26) Department of Industry and Transport Statistics, National Bureau of Statistics, P. R. C., and Energy Bureau, National Development and Reform Commission, P. R. C. China Energy Statistical Yearbook 2004; China Statistics Press: Beijing, China, 2005. (27) Ward, D. E.; Susott, R. A.; Kauffman, J. B.; Babbitt, R. E.; Cummings, D. L.; Dias, B.; Holben, B. N.; Kaufman, Y. J.; Rasmussen, R. A.; Setzer, A. W. Smoke and fire characteristics for Cerrado and deforestation burns in Brazil: BASE-B experiment. J. Geophy. Res. 1992, 97 (D13), 14601–14619. (28) Reid, J. S.; Koppmann, R.; Eck, T. F.; Eleuterio, D. P. A review of biomass burning emissions part II: intensive physical properties of biomass burning particles. Atmos. Chem. Phys. 2005, 5, 799–825. (29) Ykelson, R. J.; Susott, R.; Ward, D. E.; Reardon, J.; Griffith, D. W. T. Emissions from smoldering combustion of biomass measured by open-path Fourier transform infrared spectroscopy. J. Geophys. Res. 1997, 102, 18865–18877. (30) Hao, W.-M.; Ward, D. E. Methane production from global biomass burning. J. Geophys. Res. 1993, 98, 20657–20661. (31) Lian, J. J. Study on polycyclic aromatic hydrocarbons and their alkyl derivatives in dustfall and smog emitted from biomass burning. Ph. D. Article. Fudan University, 2009. (32) Ren, Y.; Cheng, T. T.; Chen, J. M. Polycyclic aromatic hydrocarbons in dust from computers: one possible indoor source of human exposure. Atmos. Environ. 2006, 40, 6956–6965. (33) Dhammapala, R.; Claiborn, C.; Simpson, Ch.; Jimenez, J. Emission factors from wheat and Kentucky bluegrass stubble burning: Comparison of field and simulated burn experiments. Atmos. Environ. 2007, 41, 1512–1520. (34) Zhang, Y.; Dou, H.; Chang, B.; Wei, Z.; Qiu, W.; Liu, S.; Liu, W.; Tao, S. Emission of Polycyclic Aromatic Hydrocarbons from indoor straw burning and emission inventory updating in China. Ann. N.Y. Acad. Sci. 2008, 1140, 218–227.
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