# Contribution of Wood Smoke to Particle Matter Levels in Connecticut
Source Characterization of Outdoor Wood Furnaces
Prepared by NESCAUM 

## September 9, 2008

### Members of Northeast States for Coordinated Air Use Management

Arthur Marin, Executive Director Northeast States for Coordinated Air Use Management

Paul Miller, Deputy Director Northeast States for Coordinated Air Use Management

Anne Gobin, Bureau Chief Connecticut Department of Environmental Protection, Bureau of Air Management

James P. Brooks, Bureau Director Maine Department of Environmental Protection, Bureau of Air Quality

Barbara Kwetz, Director Massachusetts Department of Environmental Protectio n, Bureau of Waste Prevention Robert Scott, Director New Hampshire Department of Environmental Services, Air Resources Division William O’Sullivan, Director New Jersey Department of Environmental Protection, Office of Air Quality Management David Shaw, Director New York Department of Environmental Conservation, Division of Air Resources Stephen Majkut, Chief Rhode Island Department of Environmental Management , Office of Air Resources

Richard A. Valentinetti, Director Vermont Department of Environmental Conservation, A ir Pollution Control Divisioniii 

# Contribution of Wood Smoke to Particle Matter Levels in Connecticut

Source Characterization of Outdoor Wood Furnaces

Prepared by NESCAUM



## September 9, 2008iv 

# C ONTRIBUTION OF 

# W OOD 

# S MOKE TO 

# P ARTICLE



# M ATTER 

# L EVELS IN 

# C ONNECTICUT


## S OURCE CHARACTERIZATION OF 

## O UTDOOR 

## W OOD 

## F URNACES

Project Manager George Allen, NESCAUM

Principal Contributors Executive Summary: George Allen, NESCAUM Chapter 1: George Allen, Lisa Rector Chapter 2: George Allen Chapter 3: George Allen Chapter 4: Lisa Rector, George Allenv



## Acknowledgments NESCAUM gratefully acknowledges the funding supportprovided by the Connecticut Department of Environmental Protection, Bureau of A ir Management, and the United States Environmental Protection Agency. NESCAUM is an ass ociation of the eight northeast state air pollution control programs that provides technical guidance and policy advice to its member states. We also acknowledge CT DEP staff that provided assi stance with the OWB testing field work: Peter Babich Joseph Kowalczyk Mark Spiro
NESCAUM also thanks the following individuals for p roviding comments on this report: Mark Spiro, Aileen Matta, and Anne Gobin – CT DEP Paul Miller – NESCAUM

Printed: September 10, 2008vi



## Executive Summary
This report was undertaken by the Northeast States for Coordinated Air Use Management (NESCAUM) for the Connecticut Department of Environ mental Protection (CT DEP) as part of an effort to assist policymakers at the national, s tate, and local levels in better understanding the contribution of the biomass burning sector to air p ollution problems and to investigate control options for reducing wood smoke emissions from outd oor wood furnaces.


### ES-1. Introduction Outdoor wood furnaces (commonly called outdoor woodboilers or OWBs) are a growing concern as large sources of wood smoke in residenti al areas in the Northeast. NESCAUM, under contract to CT DEP, performed several particu late mass (PM) stack emission (source) tests on a typical OWB (approximately 500,000 Btu p er hour input capacity, a common size for residential use) under a range of burn conditions. These tests allow us to gain a better understanding of how “burn practices” can effect st ack PM emissions and determine the range of particle emissions that could be expected to be fou nd from an in-use uncontrolled OWB. In-use here means an existing OWB installation that was ro utinely being used for space heating during the cold weather season. PM measurements were made using a continuous method (TEOM ® ) to allow us to observe short-term variations in PM emi ssions and segregate damper open from damper closed emissions. 

### ES-2. OWB Testing Protocols A total of eleven test burn days were performed dur ing four different weeks; two in October 2007, one in March and one in April, 2008. Week one used a full load of the wood (600 pounds) from the OWB owner’s woodpile. During the first test day, the unburned wood was removed after the day’s tests. During the second a nd third days of week one, a new 600 pound load was burned for two successive days. A limitednumber of speciated total (gas and particle phase) poly-aromatic hydrocarbon (PAH) samples were collected during week one of testing. Week two consisted of two test days burning the sam e Owb user’s wood but samples were collected downstream of an early prototype oxidatio n catalyst. Weeks three and four (six test days total) focused on evaluation of PM emissions o ver a wide range of burn practices. Burn practices evaluated include the type of wood (hard or soft cord-wood), the moisture content (seasoned or “green” wood), and the size (weight) o f the load relative to the volume of the burn chamber. To give some context of our tests to labo ratory emission tests, an EPA method 28 “crib” was used for one of the test days. A crib i s a structure assembled from seasoned dimensional oak lumber in a predefined way to provi de optimal burn conditions. 

### ES-3. Summary of OWB Testing Results During testing, it became clear that on a PM grams per hour basis, nearly all the emissions occurred when the OWB damper was open. T herefore, the table of emissions presented here shows the average emissions constrai ned to times when the OWB damper was open over the course of each day’s burn. All data are at standard temperature and pressure (STP), and are not corrected for water vapor or dif ferences between TEOM and Teflon filter gravimetric samples (the TEOM data are different by approximately ± 25percent). In the case of the week two catalyst tests, results are also constrained to when the catalyst was operating properly (i.e., self-firing).vii

Table ES-1. Summary of OWB Test Results: Emissions with Damper Open
Date of Test PM emissions,

grams/hour STP Wood Load

Description Wood Moisture

Content Range (%) 10/2/07 71 611 lb user’s hardwood, split 14-29

10/3/07 55 614 lb user’s hardwood, split 14-29

10/4/07 24 continued burn of 10/3 load n/a
10/10/07 (Catalyst) 12 610 lb user’s hardwood, split 14-29
10/11/07 (Catalyst) 1.5 continued burn of 10/10 load n/a

3/11/08 221 300 lb wet Hemlock Slab, 48" lengths 21-35
3/12/08 265 300 lb “kiln dry” white Pine split 11-28

3/13/08 147 300 lb “wet” mixed hardwood split 26-36

4/8/08 81 300 lb EPA Crib 14-29 4/9/08 96 300 lb seasoned hardwood, split 13-39

4/10/08 81 150 lb seasoned hardwood, split 15-37 (same

woodpile as 4/9)

Not including data from the catalyst test days, PM “damper open” emissions varied by an order of magnitude, ranging from 24 to 265 grams per hour for the same OWB. The difference in emissions on each test day was driven by burn pract ices and how long the wood had been in the OWB (day two of a two-day load burn is cleaner than day one).viii



### ES-4. Findings Summary The work completed indicates several issues that ma y require development of or revisions to existing policy to assure public health protections . The issues include: • EPA test methods for OWBs may under-represent rea l-world emissions by a factor of four; • Fuel specifications may be necessary in the futur e to ensure lowest possible emissions from wood burning; • There may be additional pollutants of concern, in cluding sulfur dioxide, naphthalene, and mercury from wood burning that may depend on the harvest location; • Add-on control technologies could significantly r educe emissions if and when they become commercially available.
4.1 Testing Protocols EPA Method 28 OWHH should be re-evaluated to more c losely approximate a worst case scenario. This would harmonize emission results fro m indoor woodstoves and OWBs and provide a better method for comparing emissions fro m residential wood burning devices. The difference in emissions from different fuels is significant, so more attention should be focused on developing fuel requirements. 4.2 Fueling Protocols This work suggests that the species of wood and moi sture content play critical roles in determining the extent of emissions from wood burni ng. It is possible that these parameters will play a critical role in emission outcomes in all wo od burning devices. 4.3 Other Pollutants than PM Emissions other than PM should be investigated further. Wood smoke contains many PAH species, especially naphthalene. SO2 emissions, atleast for eastern wood, are significant. It is likely that significant amounts of mercury are pres ent in wood smoke emissions. 4.4 Recommendations on Retrofit Technologies Little to no action has been focused on add-on tec hnology to reduce the emissions from existing units, which are a significant portion of the wood smoke related air quality problem. Based on the data obtained in this project, reducing emissio ns from existing units is technically feasible, but at this time there are no commercial retrofit p roducts available.Source characterization of Outdoor Wood Furnaces –Page 1-1

1 Schreiber, Judith et al. Smoke Gets in Your Lungs: Outdoor Wood Boilers in N ew York State . Office of the Attorney General; Albany, New York, 2005. Available at http://www.oag.state.ny.us/press/2005/aug/August 2005.pdf 

## 1. INTRODUCTION
1.1 Background and Need for Stack Testing
Due to the high cost heating fuels many people are turning to the use of wood for residential and commercial heating. Outdoor wood b oilers (OWBs), water-stoves or outdoor hydronic heaters (OWHH) create the greatest concern for public health. OWBs have been a controversial form of wood heating in the northeast ern and mid-western US and Canada for several years. The controversy is caused largely b y the smoke and health impacts the emissions from OWBs have on neighbors, but there has also bee n concern about the use of the units when burning various types of wood or for burning materi als other than natural wood. OWBs can be used in both residential and commercial applications. These units are primarily used for space heating and providing dome stic hot water. They are also used to heat swimming pools and hot tubs, and in agricultural op erations such as dairy and greenhouse operations. They come in a variety of sizes and sh apes but most look like small, freestanding metal tool sheds with stacks. Commonly, they have large fireboxes (20 cubic feet up to 150 cubic feet), which are surrounded by water jackets. The water is heated by the fire and is circulated underground via insulated pipes from the OWB to the house or other operation. The units are designed to burn large amounts of wood ov er long periods of time. 1 OWBs vary in size ranging from 115,000 Btu per hour up to 3.2 million Btu per hour, although residential OWBs tend to be less than 1 million Btu per hour. Accor ding to sales data, the size of the most commonly sold unit is 500,000 Btu per hour. OWBs h eat buildings ranging in size from 1,800 square feet to 20,000 square feet. These units are different than typical heating devi ces for the following reasons:

! Year Round Operation – OWBs are designed to provide heat and hot water year round. Owners often use them in the warmer months not only for domestic hot water but also to heat their swimming pools and/or spas.

! Cyclic Operation - The cyclic nature of OWB operati ons does not allow for complete combustion and creates an environment conducive to increased toxic and particulate emissions, unlike EPA certified wood stoves.

! Short Stack Heights – Stacks from OWBs, as per manu facturer’s installation instructions, are usually less than 12 feet from the ground, resu lting in poor dispersion of smoke and are more likely to cause fumigation within surround ing areas.

! Oversized Firebox – An OWB’s large firebox is builtsuch that a user could burn a variety of inappropriate materials that could not b e burned in wood stoves or fireplaces. Enforcement programs have discovered OWBs burning t ires, large bags of refuse, andSource characterization of Outdoor Wood Furnaces –Page 1-2

railroad ties. Even when used properly, overall OWB s emissions are greater than other residential wood burning devices. Many states have seen a significant increase in the use of these units while air emissions from them remain relatively un-characterized. The current vendor sponsored certification test data set represents new, cleaner units using a dime nsional red oak within a specific moisture content range. The limited vendor independent data available indicates that OWBs may pose a significant public health impact. Until this curre nt emissions test program, there has been no analysis to determine how fueling and use patterns can affect emissions. Emission standards have been developed to protect public health based upon the above referenced certification test. However, questions remain as to how the certificati on tests may represent real world conditions. In general, wood burning in residential or small co mmercial situations emits hundreds or even thousands times more particulate than burning oil or gas. While wood is a renewable local resource and is considered by some to be global warming neutral, more and more people choose to burn wood. The devices they use need to be more and more efficient in order to maintain the current air quality. Some long term effects of an increasing population that chooses poor wood burning technologies will be increased health care costs, premature deaths and a decreasing quality of life. The information obtained through this project will be valuable in developing control strategies and emission inventories while gaining a better understanding of the OWBs contribution to Connecticut’s PM 2.5 levels. In addition, the information developed un der this project is meant to assist in assessing the impacts of OWBs on air quality and public health. Currently, Connecticut and several other states are assessing the need to develop regulations that would require emission controls on these units. Ga ining a better understanding of OWB emissions should direct further action.


### 1.2 Project Design This OWB stack test project was limited to a single uncontrolled OWB that was in-use for heating a building. The OWB size was typical o f many installations, with a heat input of approximately 500,000 Btu per hour. The OWB was lo cated near the building, allowing us to run measurement instrumentation in a controlled env ironment and still sample from the stack without excessive sample line length. Constraining tests to a single unit allowed us to evaluate only the effect of burn practices on PM stack emiss ions. Variables included the type of wood (hard or soft, slab), the moisture content (green o r seasoned), the amount (weight) of the load used, damper status or duty cycle, and fresh load v ersus aged load emissions. There were some limitations to this work that are a result of testing an in-use field OWB. We could not measure the weight of wood actually bu rned, only the weight of the initial load and a visual inspection of the remainder of the load atthe end of the test burn. We could not measure actual heat output due to the complexity of the load plumbing used on the system. Therefore, we can not report emissions in units of mass of wood burned for a given heat input or output. We did not make measurements of stack wate r vapor, so results represent “wet” emissions. Stack water vapor is generally between 8 and 12 percent in OWBs, so this is not a large uncertainty given the very wide range of emis sions observed during the tests.Source characterization of Outdoor Wood Furnaces –Page 2-1



## 2. METHODS 2.1 Introduction Based on early experience during the OWB testing ph ase of this project, we realized that it was more practical to focus testing on a single OWB while varying the burn conditions instead of testing multiple OWBs. A 500,000 Btu per hour u ncontrolled OWB was used for all tests. The OWB we tested was heating only a portion of bui lding. This aspect of the building's plumbing prevented an accurate measurement of heat output. The damper was thermostatically controlled based on OWB water jacket temperature, b ut was manipulated manually for these tests. This facility also had an optional add-on p rototype catalytic after-burner available. This configuration allowed us to run tests with the cata lyst for one of the four test weeks to assess its performance. The burn-box volume of this OWB was measured as 60. 5 cubic feet, slightly different than the manufacturer's specification. Various wo od types (hard vs. soft, seasoned vs. green) and loads (150, 300, and 600 lb hardwood, EPA Metho d 28 crib) were used to vary the "burn practices" while keeping the OWB hardware constant. Wood moisture content was measured for each load of wood. Several moisture samples were p erformed on each of a few pieces of wood from each load. The original work plan was to perf orm two days of tests for each of the four weeks. Working at a fixed facility reduced the ove rall effort and allowed us to do three days of tests for each week except the week when the catalytic converter was tested. This approach also freed up resources to do limited speciated PAH samp ling during week one.



### 2.2 Measurement Methods

PM emissions were measured from the OWB during two weeks in October 2007, one week in March 2008 and one week in April 2008. The first two weeks of testing used a TSI/Matter Engineering Rotating Disk Dilutor (RDD), providing a 785:1 dilution ratio. SO2 was used to verify proper operation of the RDD by i ntroducing a known amount of SO2 upstream from the RDD inlet and measuring the SO2 c oncentration out of the RDD. OWB stack flows were measured by introducing a known amount o f SO2 into the stack and measuring the stack SO2 downstream; the background SO2 was subtra cted from these measurements. During week two, a prototype catalytic converter was used on the OWB; SO2 could not be used for stack flow measurements during these tests since th e catalyst converts SO2 to SO3. In addition, the OWB damper blower was used for the catalyst tes ts, since proper draft could not be obtained without it. The TSI RDD was unavailable for rental for the thir d and fourth weeks of testing. Therefore, tests for the last two weeks were done u sing an EPA-method dilution tunnel with a 110:1 dilution ratio that was built specifically fo r these tests. Tunnel flow and CO2 stack/tunnel concentration ratios were used to determine stack e missions; this work was done by the company running the dilution tunnel. Each test week consis ted of three days of sampling, except for week two. During that week, the OWB was tested with th e add-on, catalytic oxidizer for only two days. A day of testing was typically 7 to 8 hours burn duration. During tests with loads of 300 pounds or less, the load was fully charred and most ly burned at the end of the burn.Source characterization of Outdoor Wood Furnaces –Page 2-2

Other measurements include OWB stack temperature, O WB water jacket temperature (a rough indicator of heat output), wood moisture cont ent using a Delmhorst (Towaco NJ) model J-2000 meter, real-time PM measurements (TEOM) fromthe dilution system, speciated PAH (week-one only, five samples), and for the first te st using the rotating disk dilutor, a verification of dilution ratio. During the first test, stack SO 2 was also measured. A Thermo/MIE (Franklin, MA) DR-4 nephelometer was also used during the lasttwo weeks of testing; size correction was set to "off" and data were collected at 1-minute in tervals. The DR-4 data were not used, since it was clear from casual comparisons to the TEOM that the DR-4 was not able to measure the fresh smoke aerosol with any degree of consistency. PAH samples were collected using a filter/XAD-2 trap sampler and analyzed using CARB Method 429. The PAH data are the sum of both gas and particulate phase. The collection duration was four hours. Naphthalene do minates all other PAHs by a very large degree. Calculated PAH emissions in grams per hour for measured species are presented in table 3-1. A model 1400AB TEOM was used for PM measurements wi thout any size-cut inlet. Flow was reduced to 1.0 standard liters per minute, and time constants were reduced from 300/300 to 30/30 seconds. Data were recorded at 1- minute intervals. Slope and offset factors were set to 1.0 and 0 respectively. The system temperatures were set to between 20 and 30C depending on ambient dew point. This difference in filter temperature might affect results, with higher TEOM filter temperatures resulting in lower PM measurements. As a check on TEOM performance, 47-mm Teflon filter gravimetric samples were collected from the same sample location as the TEOM using Savillex filter holders. These filter samples were low flow (1 to 2 lpm) and short durati on (1-2 hours). These are conditions that minimize loss of semi-volatile PM from the filter. Samples were refrigerated immediately after collection and analyzed by CT DEP. Filters from we eks three and four were weighed both immediately after removal from refrigeration and th en again after 24-hours equilibration; there was a very consistent mass loss of 13 percent (R2 = 0.998). It is unclear if it is water or semi-volatile PM, but since the sample RH was not h igh and the sample composition being mostly organic carbon (not prone to absorbing water ), it can be assumed it is loss of volatile components of wood smoke aerosol. Another rational e that the loss is not water is that the filters were collected over a wide range of RH, and that wo uld cause a substantial range of water uptake if that were occurring. Thus, the very high correlation noted above indicates that it is unlikely that water loss that is driving the 13 per cent mass loss during filter equilibration.Source characterization of Outdoor Wood Furnaces –Page 3-1



## 3. SUMMARY OF PM EMISSION RESULTS FOR ALL TESTS 3.1 Introduction
PM emissions for these tests were characterized as grams per hour at 25C and 1013 mb (STP) and were not corrected for water vapor. Emis sions varied greatly depending on the damper mode (open or closed); damper open mode is w hen the bulk of emissions occur. Damper closed emissions are much lower and don't re ally contribute to the overall emissions because of much lower stack flows and much lower st ack PM concentrations. Taken together, these factors reduce damper closed PM emissions to a very low level, causing damper open emissions to drive the overall PM emission rates. Because of this, a mean emission rate (grams per ho ur) is sensitive to the ratio of damper open/closed time, which wasn't always the same acro ss all tests. One of the lessons learned is that having some idea of the overall OWB load with respect to the percent of time the firing air damper is open is essential in estimating average e missions for any in-use OWB. Results reported here focus on damper open PM emission rate s. It was also noted that emissions are much higher du ring the first half of the burn cycle. Emissions were especially high during the first hou r or so after a fresh load of wood. Once the wood is mostly burned to charcoal, PM emissions dro p substantially. For days when a 600 pound load was burned for two successive test days, PM emissions for the second test day were always substantially lower. Time-series plots for each run are presented below.



### 3.2 Results The emissions data presented here are constrained t o damper open mode, and are the mean pm in grams per hour. The range of percent wo od moisture content readings is also reported.


### 3.2.1 Fall tests with RDD; TEOM at 30C Oct. 2: 71 g/h 611 lb of wood on lot, seasoned har dwood for all three days in October.

Moisture: 14 to 29 percent Oct. 3: 55 g/h 614 lb fresh load of wood on lot (m oisture same as Oct. 2) Oct. 4: 24 g/h (continued burn of load from Oct. 3 - mostly charcoal)Source characterization of Outdoor Wood Furnaces –Page 3-2



### 3.2.2 Tests with catalyst The second week of fall testing was with the protot ype catalyst - these results can not be compared to other test burns. Data are constrainedto times when the catalyst was working. Catalyst performance was erratic, resulting in very different results for the two days. Moisture same as Oct. 2 (same OWB owner's wood pile): Oct. 10: 12 g/h 600 lb fresh load of wood on lot ( moisture same as Oct. 2) Oct. 11: 1.5 g/h (continued burn of Oct. 10 wood lo ad)


### 3.2.3 Dilution tunnel tests, winter/spring 2008
Week of March 11: TEOM at 20C. Mar 11: 221 g/h 300 lb wet hemlock slab; moisture range: 21-35 percent Mar 12: 265 g/h 300 lb "kiln-dry" white pine; moisture range: 11- 28 percent Mar 13: 147 g/h 300 lb "wet" mixed hardwood; moistu re range: 26 - 36 percent
Week of April 8: TEOM at 25C. Apr 8: 81 g/h 300 lb EPA Method 28 seasoned oak cr ib; moisture range: 14 - 29

percent Apr 9: 96 g/h 300 lb seasoned mixed hardwood; mois ture range: 13 - 39 percent Apr 10: 81 g/h 150 lb seasoned mixed hardwood, bu rned to end of load;

moisture range: 15 - 37 percentSource characterization of Outdoor Wood Furnaces –Page 3-3



### 3.2.4 PAH results Table 3-1. PAH Emissions PAH PAH Emissions in Grams per Hour @ STP, Wet Date 10/2/2007 10/3/2007 10/3/2007 10/4/2007 10/4/2007 naphthalene 0.83283 0.51363 3.60259 5.17109 4.94183 2-methylnaphthalene 0.02023 0.05119 0.08455 0.18409 0.07 079 acenaphthylene 0.00060 0.00164 0.00169 0.00236 0.00320 acenaphthene 0.00093 0.00187 0.00180 0.00234 0.00212 fluorene 0.00116 0.00311 phenanthrene 0.00151 0.00381 0.00323 0.00405 0.00185 anthracene 0.00023 0.00023 fluoranthene 0.00128 0.00504 0.00216 0.00121 0.00169 pyrene 0.00192 0.00650 0.00308 0.00268 benzo(a)anthracene 0.00283 0.00596 0.00143 0.00063 0.000 78 chrysene 0.00353 0.00736 0.00168 0.00061 0.07594 benzo(b)fluroanthene 0.00315 0.00047 benzo(k)fluroanthene 0.00687 0.00184 0.00035 benzo(e)pyrene 0.00094 0.00087 0.00029 0.00008 benzo(a)pyrene 0.00127 0.00149 0.00102 0.00026 0.00008 perylene 0.00018 0.00021 0.00027 0.00002 indeno(1,2,3-c,d)pyrene 0.00043 0.00083 0.00034 0.00013 0.00012 dibenzo(a,h)anthracene 0.00011 0.00024 0.00011 0.00003 benzo(g,h,i)perlene 0.00055 0.00104 0.00047 0.00014 0.00 013 PM g/h @ STP, Wet 30.7 42.9 14.5 17.1 14.5 Percent damper open: 34.7 48.3 41.3 54.7 51.3 Notes: Oct. 2 and 3 runs are with new full wood loa d; Oct. 4 is with Oct. 3's load. Empty cells indicate non-detects. Values are the s um of gas and vapor phase PAH. PM emissions match PAH sample collection time. Virtually all the PAH by mass is naphthalene for al l the samples. For the last three samples, it makes up 25 to 30 percent of the total PM emissions. While this does not mean PAHs make up that amount of the PM (since gas phase PAH is included here), it does indicate that OWBs can be very large sources of naphthalene. Additional detail on the PAH sampling method is included in the appendix to this report.Source characterization of Outdoor Wood Furnaces –Page 3-4



### 3.2.5 Summary of Results One would expect that average damper open PM emissi ons for October 2 and 3 would be somewhat similar to April 8-10, and that is what we observed. Softwood (hemlock, pine) is very dirty, as expected. Wet hardwood (maple, birch, oak) is dirtier than seasoned hardwood, again as expected. The PM emissions for seasoned hardwoo d (October 2-3 and April 8-10) are reasonably similar, giving confidence that the two different dilution methods are reasonably comparable. The EPA Method 28 crib burn was somewh at cleaner than a similar load of mixed hard cordwood, again as expected because of optimal air circulation with the crib load's construction. The smaller load of April 10 seasone d mixed hardwood was somewhat cleaner than the same but larger 300 pound load of April 9, again as expected. Time series plots for each burn day are included in the appendix to this report. There is a caveat for emission data across weeks in addition to the two different dilution methods used: the TEOM was run at different tempera tures each week for various reasons. The most important need was that filter temperature hadto be well above ambient dew point. Higher TEOM temperatures could result in lower PM measurem ents - how much is hard to estimate. A five degree C increase should not be the driver beh ind the March and April results. The gravimetric filter measurements let us control for different TEOM responses across the study; those differences varied from +30 percent to -20 pe rcent depending on the test week, and are not applied to the data presented here. Regressions of the TEOM PM vs. matching gravimetric filter data for each burn week (except the catalyst test w eek) are included in the appendix. Stack concentrations of SO2 were 20 to 30 ppm durin g the first week of tests. A sample of the wood being burned was sent to EPA for analys is. 100 ppm Sulfur was found in that sample. Presumably wet sulfur deposition is the so urce of the sulfur found in the wood, and the cause of SO2 emissions in the stack. The full elem ental analysis of that wood is presented in section 4.Source characterization of Outdoor Wood Furnaces –Page 4-1



## 4. Discussion and Conclusions 4.1 Effect on emissions due to fuel use The range in emissions of 24 to 265 grams per hour obtained from the testing program suggests that fuel type and characteristics will gr eatly affect “real-world” OWB emissions. Testing from this project indicates that fuel param eters, such as moisture content and wood species, play a vital role in determining air emiss ion outcomes. Test results showed that burning seasoned hardwood resulted in the lowest emission o utcomes. Table 4-1 displays the emissions from the hardwood loads. These data suggest that e missions from various seasoned hardwood loads occur within a small range from 55 grams per hour to 96 grams per hour. However, when the moisture content of the fuel charge increases b y 10 percent, emissions increase by 65 percent to 167 percent over those obtained with seasoned hardwood. Table 4-1. Emissions from Hardwood loads Date of Test PM Emissions,

grams/hour STP Wood Load Description Wood Moisture Content Range (%) 10/3/07 55 614 lb user’s hardwood, split 14-29 10/2/07 71 611 lb user’s hardwood, split 14-29 4/10/08 81 150 lb seasoned hardwood, split 15-37 (same woodpi le as 4/9) 4/8/08 81 300 lb EPA crib red oak dimensional lumber 14-29

4/9/08 96 300 lb seasoned hardwood, split 13-39 3/13/08 147 300 lb “wet” mixed hardwood, split 26-36 Emission tests conducted during this project (see T able 4-2) using softwood similar to that used for indoor woodstove testing indicated th at emissions from this fuel type could be 200 to 500 percent higher than those obtained from burn ing hardwood. In addition, the testing found that emissions were highest (265 g/hr) when using a fuel type similar to that used with EPA Method 28 for indoor woodstoves. This compares with an emission rate of 81 grams per hour when using the fuel type indicated with EPA Method 28 for OWBs. This indicates that the test for indoor woodstoves may be more rigorous than the test required for OWBs. Table 4-2. Emissions from Softwood Loads Date of Test PM Emissions,

grams/hour STP Wood Load Description Wood Moisture Content Range (%) 3/11/08 221 300 lb wet hemlock slab, 48” lengths 21-35 3/12/08 265 300 lb “kiln dry” white pine split 11-28 Testing indicates that emissions at the end of the fuel charge, as well as those during damper down times, may significantly underestimate short term impacts. Emissions from the continued loads represent the lowest emissions. Em issions from these loads were 50 percent to 90 percent cleaner than those from the first 8 hour s of the fuel charge (see Table 4-3). In order to determine accurate short term impacts, changes i n testing would be required to either set testing at a pre-determined time length or to use r eal-time monitoring techniques to capture changes in emissions over time.Source characterization of Outdoor Wood Furnaces –Page 4-2

Table 4-3. Emissions from end of fuel charge Date of Test PM Emissions,

grams/hour STP Wood Load Description Wood Moisture Content Range (%) 10/4/07 24 continued burn of 10/3 load n/a 10/11/07 (Catalyst) 1.5 continued burn of 10/10 load n/a


### 4.2 Issues Related to Fueling Protocols
Work could be done with EPA to revise EPA Method 28 OWHH to more closely approximate worst case scenario. Use of this optio n would harmonize emission results from indoor woodstoves and OWBs and provide a better method for comparing emissions across residential wood burning devices. There may be som e opposition from industry to this approach. One regulatory strategy would be to develop and enf orce fuel requirements for users. This option would be difficult and resource intensi ve to enforce. In addition, many states are precluded from taking enforcement actions in reside ntial situations. Emissions other than PM should be investigated further. This work suggests that the species of wood and moi sture content play critical roles in determining the extent of emissions from wood burni ng. It is possible that these parameters will play a critical role in emission outcomes in all wo od burning devices. States should consider developing fuel protocols for all wood burning sour ces, including wood pellets and wood chips, to ensure the lowest possible emission outcomes.


### 4.3 Use of Control Technologies This project tested the impact of an add-on control device to reduce emissions. This control device was external to the OWB, and was an oxidation catalyst with a propane preheater. Table 4 highlights the emission measured f rom using the prototype control device. Based on the testing, an 80 percent reduction in em issions could be obtained during high load times and a 94 percent reduction during low load ti mes. Table 4-4. Emissions from add on control devices Date of Test PM Emissions,

grams/hour STP Wood Load Description Wood Moisture Content Range (%) 10/10/07 (Catalyst) 12 610 lb user’s hardwood, split 1 4-29 10/11/07 (Catalyst) 1.5 continued burn of 10/10 load n/a



### 4.3.1 Recommendations To date, regulatory actions have focused on placing emission limits on new units. Within one year’s time, the regulatory actions have result ed in a reduction of emissions over previous units by as much as 95 percent. Little to no actio n, however, has been focused on add-on technology to address existing units, a significantportion of the air quality problem. Based on the data obtained in this project, reducing emissio ns from existing units is technically feasible. ItSource characterization of Outdoor Wood Furnaces –Page 4-3

is likely that emissions from existing OWBs could b e reduced significantly if programs were put in place that require the use of add-on control tec hnologies or require emission limits on the existing fleets of OWBs. However, there are no com mercially available retrofit technologies available at this time.



### 4.4 Other Pollutants of Concern The primary pollutant of concern from wood burning has traditionally been particulate matter, PAHs, and POMs. Under this work, NESCAUM a lso completed elemental analysis of a limited sample of the fuel used for testing. This analysis revealed elemental sulfur levels fifty times higher than anticipated based on EPA studies. While the data set completed under this project is too limited to make conclusive findings, it does raise concerns regarding the potential emissions of other pollutants, especially in areas prone to acid deposition and other pollutants often related to the burning of coal. Specific pol lutants of concern include sulfur dioxide and mercury. To this day, there has been no study of the elemental constituents of wood in the Northeast. Based upon these preliminary findings, NESCAUM recommends that emission tests on all wood burning in the Northeast should include characterization of sulfur dioxide and mercury emissions. Additionally, research regardin g the effects of soil constituents and air pollution on the elemental composition of wood woul d provide further insights. Table 4-5. Elemental analysis of OWB owner’s wood

## Appendices

1. Eleven time series plots of grams per hour PM e missions and stack mode/temperature 2. TEOM vs. filter scatter-plots for weeks 1, 3, a nd 4 3. Scatter-plot of mass loss over 24 hour filter e quilibration for weeks 3-4 4. PAH Laboratory report excerpt and documentatio n of sample run times and volumes.