Emissions from Residential Wood Combustion: Activity Data Survey and Results

Transcription

1 Emissions from Residential Wood Combustion: Activity Data Survey and Results Control # 103 Chun Yi Wu Minnesota Pollution Control Agency, 520 Lafayette Road North, St. Paul, MN Jean Mouelle, Keith L Jacobson Minnesota Department of Natural Resources, 500 Lafayette Road North, St. Paul, MN Ronald Piva U.S. Department of Agriculture, Forest Service, North Central Research Station, 1992 Folwell Ave., St. Paul, MN John Crouch HPBA - Hearth Patio,& Barbecue Association, Sacramento office, 7840 Madison Ave suite 185, Fair Oaks, CA ABSTRACT The National-Scale Air Toxics Assessment (NATA), conducted by U.S. EPA for calendar year 1996, indicated that modeled statewide median concentration of Polycyclic Organic Matter (POM) for Minnesota exceeded a health benchmark, with a significantly higher value compared with other states. Residential wood combustion was the greatest contributor to this pollutant. In preparing the 1996 data, Minnesota Pollution Control Agency (MPCA) followed EPA's guidance in compiling the emissions inventory for residential wood combustion. The activity data (fuelwood consumption) were obtained from a survey conducted by the Minnesota Department of Natural Resources (DNR) for the heating season. These data were believed to be the more accurate than generic activity data used by EPA for other states in the 1996 NATA. According to previous DNR surveys, there has been a decline in the fuelwood burned by residential households. This decline is expected to continue for a variety of reasons. Therefore, an activity data survey for residential wood combustion for the 2002 emission inventory was conducted. Four organizations participated in the process to accurately gauge the amount and type of residential fuelwood burned in Minnesota: DNR; MPCA; North Central Research 1

2 Station, U.S. Forest Service, U.S. Department of Agriculture; and the Hearth, Patio, & Barbecue Association (HPBA) which is the national trade association for wood, gas, and wood pellet burning fireplaces and heaters. This paper describes the survey design, methodology, results, and analyzes the impact of survey data to air toxics emissions. It shows a great improvement in accuracy for the emission inventory, which is important for the determination of the effectiveness of specific regulatory or voluntary management actions, such as the wood stove exchange program. INTRODUCTION The National-Scale Air Toxics Assessment (NATA), conducted by U.S. Environmental Protection Agency (EPA) for calendar year 1996, indicated that modeled statewide median concentration of Polycyclic Organic Matter (POM) for Minnesota (0.299 µg/m 3 ) exceeded a health benchmark for cancer (0.182 µg/m 3 ). 1 The health benchmarks for cancer represent the concentrations that are associated with an upper-bound excess lifetime cancer risk of 1 in 100,000. The Minnesota statewide median concentration of POM was also significantly higher than other states. The modeled nationwide median concentration of POM was µg/m 3, about one fifth of the Minnesota value. Approximately 8.4% of nationwide POM emissions were from Minnesota. 2 In this assessment, POM refers to 16 individual polycyclic aromatic hydrocarbon compounds (PAHs). Residential wood combustion was the greatest contributor to 16 PAH emissions. The 1996 NATA used emission estimates from the Minnesota Pollution Control Agency (MPCA) for the residential wood combustion. In preparing the 1996 data, MPCA staff followed EPA's guidance in compiling the emissions inventory for this category. The activity data (fuelwood consumption) were obtained from a survey conducted by the Minnesota Department of Natural Resources (DNR) for the heating season. 3 These data were believed to be more accurate than generic activity data used by EPA for other states in the 1996 NATA. However, according to previous DNR surveys, there has been a decline in the mount of wood burned by private households. This decline is expected to continue for a variety of reasons. Therefore, fuelwood consumption for the heating season does not represent current year activities. There is a need for current figures in order to obtain an emission inventory that is more accurate as well as to manage Minnesota forest resources more effectively. An activity data survey for residential wood combustion for the heating season was conducted. Four organizations participated into the processes to accurately gauge the amount and type of residential fuelwood burned in Minnesota. These organizations include DNR; MPCA; North Central Research Station, U.S. Forest Service, U.S. Department of Agriculture (USFS); and the Hearth Patio, & Barbecue Association (HPBA) which is the national trade association for wood, gas, and wood pellet burning fireplaces and heaters. The objectives of this survey were to Estimate the total volume of residential fuelwood harvested and consumed in Minnesota during the heating season, 2

3 Identify the sources of residential fuelwood (if fuelwood was purchased, given free, or self-harvested). Estimate the volume of residential fuelwood harvested from different land ownerships, live and/or dead trees, logging residue, and/or scrap lumber. Determine the geographic distribution of households burning fuelwood by type of usage (primary heating source, supplemental heating source, or for pleasure), and the type of wood burning appliance used. Identify trends in residential fuelwood consumption over time. Estimate air pollutant emissions from residential wood combustion. The focus of this paper is on emissions from residential wood combustion. METHDOLOGY The survey sample was based on the total number of households statewide from the 2002 Census that was obtained from the State Demographic Center. 4 The state was divided up into five U.S Forest Service Units for Minnesota Forests, with the seven metropolitan counties broken out as an additional unit. The regions included Aspen-Birch, Northern Pine, Central Hardwoods, Metro, and Prairie regions as shown on the map below (Figure1). Figure 1. Map of Survey Units. Northern Pine Aspen-Birch Central Hardwoods Prairie Metro 3

4 The basic population and housing data for counties from the Bureau of the Census indicated that there was no significant change in the number of households from previous fuelwood study in Since all regions have at least 100,000 households, the sample size was stratified into five regional groups. Previous studies were designed to have a sampling error of plus/minus six percentage points at 95% confidence level. Based on calculations from the Minnesota Center for Survey Research at the University of Minnesota, it was determined that 267 completed surveys for each region would give the same sampling error. Survey Sampling, Inc. (Fairfield, CT), which provided the mailing list, estimated the number of survey questionnaires to be mailed out by factoring in the rate of deliverable mails at 85%, and the expected response rate at 35%. The total number of questionnaires mailed was 6,600. To mitigate the lower response rate for mailing survey questionnaires, a postcard was mailed in May 2003 two weeks before the survey questionnaire was sent out to alert potential respondents of the upcoming survey questionnaire. When the expected number of responses was not obtained from the mail survey questionnaires, a selection of names were picked at random from the mailing list, and a telephone interview was used to complete the study. A combination of mail survey questionnaires and telephone interviews was cost-effective. The questions in the survey questionnaires were kept simple and brief. Specific questions for the purpose of emission inventories were also included. For example, 8 types of wood burning facilities were listed; brand name and certification status were asked. This kind of information was not provided in previous residential wood combustion surveys. RESULTS AND DISCUSSION A total of 1,408 households responded to the survey. Table 1shows the number of households responded to the survey by survey unit. Residential fuelwood consumption was analyzed by reason for burning, by type of wood-burning facility, by burning tenure, by type of fuelwood, and by wood species group. Results also show household possession and use of wood-burning facilities, size of fuelwood purchased, and place of consumption (Primary, Secondary residence, ). Percentage of households burning wood (Table 2) was higher in the two north survey units (Northern Pine and Aspen-Birch) than in the other three units. The total volume of wood burned in Minnesota decreased from 751,215 cords in the heating season to 665,463 cords in the heating season. Table 1. Households sampled by survey unit. Total Number of Survey Unit Number of Households Responded Households in Population in Aspen-Birch , ,653 Central Hardwoods ,520 1,008,558 Metro 252 1,053,853 2,708,916 Northern Pine , ,585 Prairie , ,949 4

5 Total Number of Survey Unit Number of Households Responded Households in Population in Total 1,464 1,953,636 5,033,661 Table 2. Households burning wood by survey unit in the heating season. Survey Unit Households With Wood-Burning Facilities Households Burning Wood Percent of Households Burning Wood Volume of Wood Burned (Cord) Aspen-Birch 37,576 32, ,415 Central Hardwoods 77,169 62, ,187 Metro 295, , ,296 Northern Pine 44,579 35, ,506 Prairie 58,153 41, ,059 Total 513, , ,463.1 The wood consumption data were summarized into 10 categories of wood-burning facilities, and three types of wood burned: manufactured logs/pellets, roundwood, and wood residues. Table 3 shows the volume of wood burned by each category of wood-burning facilities. The largest amount of wood was used in regular fireplaces. Table 3. Volume of wood burned by facility category (in cords). Category of Wood-Burning Facility Manufactured Logs/Pellets Roundwood Wood Residues Total Regular Fireplace 10, , , ,102.2 Fire Pit/Ring , , ,936.2 Modified Fireplace/Insert , , ,696.8 Certified Non-Catalytic Fireplace Insert ,323.7 Certified Catalytic Fireplace Insert Conventional Woodstove 1, , , ,393.6 Wood Burning Boiler 1, , , ,549.9 Wood Burning Furnace , , ,035.4 Certified Catalytic Woodstove , , ,024.4 Certified non-catalytic woodstove 23, , ,416.8 Grand Total 16, , , ,

6 Although it was attempted to collect detailed information on facility types, uncertainties were associated with survey results due to a wide variety of brands and models in the hearth product industry. The variability in terms associated with residential wood combustion facilities and fuels may cause confusion in survey respondents. Respondents that were uncertain of the detailed category of wood-burning facility were included in the generic categories: conventional woodstove, regular fireplace, and modified fireplace/insert. In order to use the survey results in emission inventory, wood-burning facilities need to be classified with Source Classification Codes (SCCs) and the volume of wood (cords) need to be converted into the mass of wood (tons). Table 4 shows the map of facility category to SCC. Fireplace inserts are woodstoves designed to fit into an existing fireplace cavity. Generally, regular fireplace, non-epa-certified fireplace inserts, and conventional woodstoves have no emission control and have high emissions. Catalytic woodstoves and fireplace inserts that are certified by EPA use a built-in catalyst to reduce emissions. Non-catalytic woodstoves and fireplace inserts that are certified by EPA reduce emissions with the design technology. Table 4. Mapping of facility category to SCC. Category of Wood-Burning Facility SCC Description SCC Regular Fireplace Fireplaces: General Fire Pit/Ring Fireplaces: General Modified Fireplace/Insert Fireplaces: Inserts - non-epa-certified Certified Non-Catalytic Fireplace Insert Fireplaces: Inserts - Non-catalytic, EPA-certified Certified Catalytic Fireplace Insert Fireplaces: Inserts - Catalytic, EPA-certified Conventional Woodstove Woodstoves - Conventional Wood Burning Boiler Woodstoves - Conventional Wood Burning Furnace Woodstoves - Conventional Certified Catalytic Woodstove Woodstoves Catalytic, EPA-certified Certified Non-Catalytic Woodstove Woodstoves - Non-catalytic, EPA-certified The density of manufactured logs/pellets was determined as Tons/Cord based on the information provided by OMNI Consulting Services, Inc. 5 The density of wood residues was estimated as Tons/Cord by the U.S. Department of Agriculture, Forest Service, North Central Research Station. 6 The density of roundwood, Tons/Cord, was calculated as a weighted average density of 13 species burned in the state. 7 The mass of wood burned for each SCC is shown in Table 5. For a comparison, the mass of wood burned for each SCC in the heating season was also estimated based on the previous survey that was conducted for the heating season and adjusted with total household numbers in For the 1996 survey data, it was assumed that 92% of wood by weight were burned in non-epa-certified facilities; 5.7% in certified, non-catalytic; and 2.3% in certified, catalytic for all types of facilities except regular fireplace. 7 This assumption was made because of a lack of information on the survey for The total mass of wood burned in the heating season based on the 6

7 current survey is 82.2% of the mass based on the 1996 survey. The percentage of wood burned by weight in each SCC does not show a significant change. Table 5. Mass of wood burned by SCC in the heating season. SCC Wood Burned Based on the Current Survey (Ton) Percent of Wood Burned Based on the Current Survey Wood Burned Based on the 1996 Survey (Ton) Percent of Wood Burned Based on the 1996 Survey , , , , , , , , , , , , , , Total 795, , Air pollutant emissions from residential wood combustion were estimated by using emission factors from the 2002 EPA s draft documentation for area source. 9 In this document, emission factors are only available for dioxins and criteria pollutants for SCC , general fireplace. However, there is no reason to assume that no emissions of other pollutants, such as PAHs, came from general fireplaces. Therefore, emission factors for other pollutants for SCC were used for SCC Table 6 shows estimated emissions of air pollutants from residential wood combustion in the heating season. The percent difference in Table 6 was calculated as the difference of emissions estimated based on the current survey and emissions estimated based on the 1996 survey divided by emissions estimated based on the 1996 survey. Overall, total emissions estimated based on the current survey are 81.4% of those based on the 1996 survey. A similar pattern is observed for emissions of pollutant groups and most pollutants. Higher emissions were estimated only for several pollutants based on the current survey than based on the 1996 survey. This is due to a lack of emission factors of these pollutants for some SCCs. Table 6. Emissions of air pollutants from residential wood combustion in the heating season. State Total on the 1996 State Total on the Current Percent Difference Pollutant Cas No. 1,2,3,4,6,7,8- Heptachlorodibenzodioxin E E Dioxins 1,2,3,4,6,7,8-Heptachlorodibenzofuran E E ,2,3,4,7,8,9-Heptachlorodibenzofuran E E ,2,3,4,7,8-Hexachlorodibenzodioxin E E

8 State Total on the 1996 State Total on the Current Percent Difference Pollutant Cas No. 1,2,3,6,7,8-Hexachlorodibenzodioxin E E ,2,3,7,8,9-Hexachlorodibenzodioxin E E ,2,3,4,7,8-Hexachlorodibenzofuran E E ,2,3,6,7,8-Hexachlorodibenzofuran E E ,2,3,7,8,9-Hexachlorodibenzofuran E E ,3,4,6,7,8-Hexachlorodibenzofuran E E Octachlorodibenzodioxins, All Isomers E E Octachlordibenzofurans, All Isomers E E ,2,3,7,8- Pentachlorodibenzodioxin E E ,2,3,7,8- Pentachlordibenzofuran E E ,3,4,7,8- Pentachlordibenzofuran E E ,3,7,8-Tetrachlorodibenzo-P-Dioxin E E ,3,7,8-Tetrachlorodibenzofuran E E Dioxins Total 6.01E E PAH Acenaphthene E E Acenaphthylene E E Anthracene E E Benz[a]Anthracene E E Benzo[a]Pyrene E E Benzo[b]Fluoranthene E E Benzo[g,h,i,]Perylene E E Benzo[k]Fluoranthene E E Chrysene E E Dibenzo[a,h]Anthracene E E Fluoranthene E E Fluorene E E Indeno[1,2,3-c,d]Pyrene E E Naphthalene E E Phenanthrene E E Pyrene E E PAH Total 4.20E E Other HAPs Benzene E E Benzo(e)Pyrene E E Benzo(g,h,i)Fluoranthene E E Biphenyl E E Cadmium Compounds 2.05E E Dimethylbenz(a)Anthracene E E Manganese Compounds 1.58E E Methyl Ethyl Ketone E E Nickel Compounds 1.32E E o-xylene E E Perylene E E Toluene E E

9 State Total on the 1996 State Total on the Current Percent Difference Pollutant Cas No. Other HAP Total 2.99E E Criteria Pollutant CO 1.61E E NOX 2.57E E PM E E PM E E SO2 3.87E E VOC 1.10E E Criteria Pollutant Total 3.19E E Grand Total 3.22E E CONCLUSIONS The amount of fuelwood burned by private households continues to decline in Minnesota. A comparison of air pollutant emissions in 2002 estimated based on the current survey and the 1996 survey indicated an overall reduction of 18.6%. However, the mass distribution of fuelwood burned by facility types (SCC) did not change significantly. Therefore, it is necessary to promote specific regulatory or voluntary management actions, such as the wood stove exchange program, to further reduce emissions from residential wood combustion. A periodic activity data survey for residential wood combustion is necessary for a more accurate emission inventory as well as for more effective management of forest resources. ACKNOWLEDGEMENTS The authors would like to appreciate Mr. Rick Dahlman (DNR) and Dr. James E. Houck (OMNI Consulting Services, Inc., Beaverton, Oregon) for their inputs on the activity data survey. REFERENCES 1. U.S. EPA, National-Scale Air Toxics Assessment Results: Modeled Ambient Concentrations, U.S. Environmental Protection Agency: Research Triangle Park, NC. (accessed January 2004). 2. U.S. EPA, National-Scale Air Toxics Assessment Results: Emissions: Data Tables, U.S. Environmental Protection Agency: Research Triangle Park, NC. (accessed January 2004). 3. Minnesota Residential Fuelwood Survey: Heating Season, Minnesota Department of Natural Resources: St. Paul, MN, Minnesota State Demographic Center. Population and household estimates. (accessed January 2004). 9

10 5. Comments on Minnesota Residential Wood Combustion Survey, Houck, J.E., OMNI Consulting Services, Inc., Beaverton, Oregon, July Release No. 232, Cord-Cubic Volume of Relationship of Slabwood and Edgings, Bell, G. E. and Brooks, E., American Pulpwood Association. New York, NY, Extension Circular 1023, Hansen, H.J., Oregon State University, Corvallis, Oregon, Sept U.S. EPA, Documentation for the Final 1999 Nonpoint Area Source National Emission Inventory for Hazardous Air Pollutants (Version 3), U.S. Environmental Protection Agency: Research Triangle Park, NC, Aug ftp://ftp.epa.gov/emisinventory/finalnei99ver3/haps/documentation/nonpoint/nonpt99ver3_a ug2003.pdf (accessed March 2004). 9. Huntley, R., Draft Documentation for the 2002 Nonpoint Area Source National Emission Inventory for Hazardous Air Pollutants, U.S. Environmental Protection Agency: Research Triangle Park, NC, Dec KEY WORDS Residential wood combustion, Fuel wood, Air toxics, Emission inventory, Minnesota 10