An Overview of Particulate Matter, Health, Biomass Combustion, and Wood Smoke

An Overview of Particulate Matter, Health, Biomass Combustion,
and Wood Smoke
Benjamin Hallowell, MPH
May 28th, 2014
This white paper was written with the support of ClearStak LLC. This paper aims to provide a
factual, non-industry biased view of the topics addressed and in no way aims to condone, or
disapprove of any biomass combustion, or associated products mentioned in this paper.
This paper will continue to be revised as new data becomes available. For the most up-to-date
copy of this paper, please visit www.ClearStak.com
1 Table of Contents
Introduction……………………………………………………………………………….………3
Defining Particulate Matter ………………………………………………………………………3
Sources of Outdoor Ambient Particulate Matter………………………………………………….3
Sources of Indoor Ambient Particulate Matter……………………………………………………6
Standards on Ambient Particulate Matter Concentrations……………………...………………....7
Air Quality Index…………………………………………………………………………….........8
Health Affects of Particulate Matter and Wood smoke…….…………………………..................9
Wood smoke…………………………………………………………………………..…………12
Mitigation…………………………………………………………………………….……...…...13
Future Work………………………………………………………………………...……………18
Work Cited……………………………………………………………………………………….20
2 Introduction
This paper was written in response to the revised NSPS for new residential wood heaters,
and aims to provide an overview of particulate matter, biomass combustion, wood smoke, and
associated health effects. For the most current version of this paper, please visit
www.ClearStak.com.
Defining Particulate Matter
Particulate matter (PM), or particle pollution, is a mixture of solid particles and liquid
droplets that are suspended in air. PM can be generated from either natural or manmade sources,
and can be composed of acid, organic, metal, soil, or dust particles (EPA 2013). PM is classified
by their aerodynamic equivalent diameter (AED), and are generally placed in one of three
categories: AED <10 microns = PM10, < 2.5 microns = PM2.5, and < 0.1 microns = PM0.1.
Particulate matter is considered coarse when between 2.5-10 microns, fine when less than 2.5
microns, and ultrafine (or nanoparticles) when less than 0.1 microns in diameter. Using these
definitions PM10 includes all course, fine, and ultrafine particulate matter. Because PM larger
than 10 microns is filtered out through the nose, cilia, and mucus of the respiratory tract, they are
of lesser public health concern (EPA 2013). Particulate matter begins to effect health when
particles are present that are smaller than 10 microns, PM10, and as such, these are the particles
and exposures that are most often studied.
Sources of Outdoor Ambient Particulate Matter
The US Environmental Protection Agency (EPA) classifies particulate matter into eight
categories, or source sectors, including: agriculture, dust, fires, fuel combustion, industrial
processes, miscellaneous, mobile, and solvent sources (EPA 2014). See Table 1.
3 Table 1: Emission source sectors and detailed category names
Major Source
Detailed Category Names
Sectors
Agriculture
-Fertilizer Application
-Crops & Livestock Dust
-Livestock Waste
Dust
-Construction Dust
-Paved Road Dust
-Unpaved Road Dust
Fires
-Prescribed Fires
-Wildfires
-Agricultural Field Burning
Fuel Combustion
-Commercial/ Institutional
(Biomass, Coal, Natural Gas,
Oil, or Other)
-Electric Generation
(Biomass, Coal, Natural Gas,
Oil, or Other)
-Industrial Boilers, ICEs (Biomass,
Coal, Natural Gas, Oil, or Other)
-Residential (Biomass, Coal,
Natural Gas, Oil, or Other)
Industrial Processes
-Non-ferrous Metals
-Oil & Gas Production
-Petroleum Refineries
-Pulp & Paper
-Storage and Transfer
-Cement Manufacturing
-Chemical Manufacturing
-Ferrous Metals
-Mining
-NEC
Miscellaneous
-Bulk Gasoline Terminals
-Commercial Cooking
-Gas Stations
-Miscellaneous Non-Industrial
-Waste Disposal
Mobile
-Aircraft
-Commercial Marine Vessels
-Locomotives
-Non-Road Equipment
(Diesel, Gasoline, or Other)
-On-Road Diesel Heavy or Light
Duty Vehicles
-On-Road Gasoline Heavy or Light
Duty Vehicles
Solvent
-Consumer & Commercial
Solvent Use
-Degreasing
-Dry Cleaning
-Industrial Surface Coating &
Solvent Use
-Non-Industrial Surface Coating
-Graphic Arts
Note: Table Adapted from: EPA. (2014). Air Emission Sources: Basic Information. Retrieved
from: http://epa.gov/air/emissions/basic.htm
4 In 2011, the EPA conducted a national summary of particulate matter emissions, and
organized the data based on particulate type (PM10 vs. PM2.5) and source sector (see Table 2
below; PM0.1 was not included in the EPA survey).
Table 2: PM10 Emissions by Source Sector, 2011
Source Sector
Total PM10 Emissions
(tons)
10,960,570
Total PM2.5 Emissions
(tons)
1,262,785
Agriculture
4,502,018
896,727
Fires
2,802,463
2,329,087
Fuel Combustion
947,462
805,751
Industrial Processes
863,280
324,550
Mobile
509,588
416,173
Miscellaneous
290,832
258,227
4,494
4,012
Dust
Solvent
Total
20,880,707
6,297,312
Note: Table Adapted from: EPA. (2011). Air Emission Sources: Particulate Matter. Retrieved
from: http://www.epa.gov/cgi-bin/broker?_
service=data&_debug=0&_program=dataprog.national_1.sas&polchoice=PM
Table 3 displays the PM10 and PM2.5 emissions by source sector for biomass combustion
products in the US. Fuel combustion generates 4.5% of all PM10 and 13% of all US PM2.5
emissions listed in Table 2. Biomass combustion products, a subset of fuel combustion, account
for 2.5% of all national PM10 emissions, and 8.1% of all national PM2.5 emissions. In some
communities, particularly in the winter months, biomass combustion’s contribution to ambient
PM levels are even more significant, with levels as high as 42-56% in some communities (Bari et
al., 2009; McGowan et al., 2002; Schauer & Cass 2000; Naeher et al., 2007; [56%] Gibson et al.,
2011; [42%] Fairley 1990; [49%] Larson et al., 2004).
5 Table 3: PM10 and PM2.5 Emissions from Biomass Combustion Products, 2011
Source Sector
Total PM10 Emissions
(tons)
13,123
Total PM2.5 Emissions
(tons)
11,229
2,182
1,873
Industrial Boilers
122,776
104,876
Residential
390,302
389,569
Commercial
Electric Generation
Total
528,383
507,547
Note: Table Adapted from: EPA. (2011). Air Emission Sources: Particulate Matter. Retrieved
from: http://www.epa.gov/cgi-bin/broker?_
service=data&_debug=0&_program=dataprog.national_1.sas&polchoice=PM
Sources of Indoor Ambient Particulate Matter
Previous studies have found that there is a high correlation between outdoor, indoor, and
personal PM exposures, with changes in outdoor PM levels often reflected in indoor/personal
exposures (Janssen et al., 2000; Janssen et al., 1998; Monn 2000). As one might expect, the
correlation between indoor, outdoor, and personal PM levels becomes stronger as particulate size
decreases (Monn 2000). Due to this, outdoor ambient PM2.5 levels are often used as a surrogate
for indoor and personal PM exposure (Monn 2000). Outdoor PM is second only to smoking in
contaminating indoor air (Monn 2000). In the absence of this or other human activity, about 70%
of indoor PM comes from outside sources (Monn 2000; Ozkaynak et al., 1996; Monn et al.,
1997). Personal PM exposures often exceed indoor and outdoor values due to various indoor
sources or human activity, including: cooking, the use of gas appliances, dusting, vacuum
cleaning, smoking, time spent in a vehicle, and human activity (as this re-suspends settled PM;
Janssen et al., 1998; Monn 2000; Weisel et al., 2005; Monn et al., 1997). In the presence of
these indoor sources, the percentage of PM attributed to outdoor sources drops to about 50%
(Janssen et al., 1998; Monn 2000; Weisel et al., 2005; Monn et al., 1997). Cooking, along with
6 cleaning, smoking, and human activity are the dominant indoor sources of PM10 (Jones et al.,
2000). Cooking and smoking are the major sources of indoor PM2.5 (Jones et al., 2000). It is
important to note that these studies were not done in homes heated with indoor or outdoor
biomass combustion products. Few studies have been conducted in developed countries to
monitor the impact of these units on indoor and personal PM exposure levels. It is hypothesized
that indoor and outdoor biomass combustion units, specifically non-epa certified units, could
significantly impact these exposures.
Standards on Ambient Particulate Matter Concentrations
The Clean Air Act requires the EPA to set National Ambient Air Quality Standards
(NAAQS) for air pollutants that could be considered harmful to public or environmental health.
Under the Clean Air Act, the EPA establishes primary and secondary air quality standards.
Primary standards are to protect the public health, as well as sensitive populations, including
individuals with respiratory morbidities, children, and elderly. Secondary standards protect the
environment, and are established to avoid creating adverse environmental effects that could
negatively impact human health (EPA 2012). As primary standards are intended to prevent
harmful short-term or long-term exposures, standards are set for average daily, and yearly,
exposures. In order to stay in compliance with NAAQS ambient air standards, PM2.5
concentrations cannot exceed an annual mean of 12 µg/m3 or a 24-hour mean of 35 µg/m3 (EPA
2012). PM10 concentrations cannot exceed a 24-hour mean of 150 µg/m3 (EPA 2012).
Currently, there is no annual mean regulation for PM10 concentrations set by the EPA (EPA
2012). If the 24-hour or annual PM2.5 level is exceeded once, or if the 24-hour PM10 level is
exceeded more than once in a year, that area or state is considered in non-attainment of NAAQS
standards (EPA 2012). If the state does not develop a State Implementation Plan to address the
7 issue and improve air quality, the Federal government may develop a Federal Implementation
Plan that the state would be forced to enact. As new highways could potentially increase air
pollution, states/areas that are in nonattainment of NAAQS standards are subject to the
withholding of federal transportation funding. In addition, the EPA may withhold all, or part, of
the grant funding it gives to the state that supports air quality monitoring, planning, and control
programs.
Contrary to the standards set by the EPA, the World Health Organization’s (WHO) Air
Quality Guidelines states that PM2.5 levels should not exceed an annual mean of 10 µg/m3, or a
24-hour mean of 25 µg/m3 (WHO 2014). The WHO Air Quality Guidelines state that PM10
levels should not exceed an annual mean of 20 µg/m3 and a 24-hour mean of 50 µg/m3 (WHO
2014). The WHO encourages all countries to take steps to attain these guideline values due to
the significant reduction that would take place in acute and chronic health morbidities associated
with elevated PM exposure (WHO 2014).
Air Quality Index
Using 24-hour pollutant concentrations, the EPA translates PM levels into an Air Quality
Index (AQI) score, which ranges from 0-500. Higher values on the AQI scale are based off of
the proportion of the population that is exposed to the pollutant, and the severity of the negative
health affects for the level of exposure, as can be seen below in Table 4.
8 Table 4: AQI Scores for PM2.5 and PM10 24-hour emission levels.
0-50
PM2.5 (µg/m3)
24-hour
0-12.0
PM10 (µg/m3)
24-hour
0-54
Moderate
51-100
12.1-35.4
55-154
Unhealthy for Sensitive Groups
101-150
35.5-55.4
155-254
Unhealthy
151-200
55.5-150.4
255-354
Very Unhealthy
201-300
150.5-250.4
355-424
Hazardous
301-400
250.5-350.4
425-504
Category
Good
AQI Value
401-500
350.5-500.4
505-604
Note: Table Adapted from: EPA. (2012).“National Ambient Air Quality Standards for
Particulate Matter; Final Rule,” 78 Federal Registry 10. (December 14th, 2012), pg 3086-3287.
Health effects of PM and Wood Smoke
Particulate matter begins to effect health when particles are present that are smaller than
10 microns, PM10, as larger particles are generally filtered out through the nose, cilia, and mucus
in the respiratory tract (EPA, 2013). These particles can settle in the lungs and bronchi and begin
to cause structural damage to the lungs. The size of greatest concern though is PM2.5 and PM0.1
as they are small enough to enter the alveoli of the lungs and travel into the blood stream
(American Lung Association 2008).
While particulate matter itself can do structural damage to the lungs, a major concern is
the other substances, specifically carcinogenic or toxic compounds, that these particles can carry
into an individual’s lungs and blood stream including: free radicals, hydrocarbons (PAHs,
benzene, and styrene), aldehydes, and phenols (Naeher et al., 2007; Leonard et al., 2000; Pryor,
1992; Schauer et al., 2001). It is important to note that while these chemicals are proven to cause
cancer, both in human and animal models, very little research has been done to study the health
9 effects and levels of exposure of these compounds when exposed via wood smoke (EPA 2008).
This was further confirmed in 2006 when the International Agency for Research on Cancer (in
Volume 95 of the IARC Monographs) declared smoke from biomass combustion products as
probably carcinogenic to humans (Group 2A), based off of limited evidence on the
carcinogenicity of biomass combustion emissions in humans and experimental animals,
sufficient evidence on the carcinogenicity of wood-smoke in experimental animals, and strong
evidence for the carcinogenicity of biomass combustion emissions in the mechanistic data (Straif
et al., 2006). If further research was conducted that confirmed the carcinogenicity of biomass
emissions to humans, however, biomass combustion emissions would be classified as a Group 1,
carcinogenic to humans. The health effects of particulate matter, however, have been
extensively studied both generally and through wood smoke exposure.
The American Lung Association and the American Heart Association has connected
short-term (hours or days) exposure to elevated particulate matter levels to a variety of negative
health outcomes including:

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
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increased deaths from respiratory and cardiovascular causes (Dominici et al., 2002; Hong
et al., 2002; Tsai et al., 2003; Brook et al., 2010)
increased number of heart attacks, specifically in individuals with previous underlying
heart conditions (D’Ippoliti et al., 2003; Brook et al., 2010)
increased hospitalizations for asthma and respiratory causes among children (Lin et al.,
2002; Norris et al., 1999; Tolbert et al., 2000)
increased hospitalizations for cardiovascular disease (Metzger et al., 2004; Tsai et al.,
2003)
increased ER visits among individuals with pre-existing respiratory problems (Van Den
Eeden et al., 2002)
increased severity of asthma attacks among children (Tsai et al., 2003)
increased mortality (Anderson et al., 2012)
increased medication usage (Anderson et al., 2012)
decreased lung function (Anderson et al., 2012)
and inflammation of lung tissue among healthly individuals (Ghio et al., 2000; Barregard
et al., 2006)
The American Lung and Heart Associations have also linked long term exposure to elevated
10 levels of particulate matter to higher rates of lung cancer, decreased lung function among
children and teenagers, overall lung damage, increased risk of cardiovascular morbidity and
mortality, and decreased life expectancy (American Lung Association 2008; Brook et al., 2010).
Adults over 65, children under 18, individuals with chronic lung conditions (asthma, chronic
bronchitis, emphysema), individuals with cardiovascular disease, and individuals with diabetes
are at higher risk for these problems (American Lung Association 2008; Brook et al., 2010). The
state of Washington estimated that “…the total cost of these diseases (not counting premature
deaths) for citizens, businesses, and state health care institutions is about $190 million each year
[in Washington State]. Total cost includes medical care, prescription drugs, reduced productivity,
lost work time, and missed school days” (State of Washington 2012).
The Harvard Six Cities cohort study found that for each 10 µg/m3 increase in PM2.5 levels,
the risk of all-cause mortality, cardiovascular mortality, and lung cancer mortality went up 14%,
26%, and 37% respectively (Lepeule et al., 2012). Lepeule et al., found that the linear
concentration response relationship remained significant to outdoor ambient PM2.5 concentrations
as low as 8 µg/m3 (Lepeule et al., 2012).
The EPA evaluated the impact of particulate matter exposure in nine cities (Detroit, Los
Angeles, Philadelphia, Pittsburgh, St. Louis, Boston, Phoenix, Seattle, and San Jose) and found
that it could be attributed to over 4,700 premature deaths annually (American Lung Association
2008). While this estimate was only for the nine cities studied, estimates nationally remain in the
tens of thousands annually, with some studies predicting in excess of 60,000 premature deaths
annually (State of New York 2008; American Lung Association 2008). In fact, the WHO
estimates that particulate matter emissions is responsible for approximately 800,000 premature
deaths each year, making it the 13th leading cause of death globally (Anderson et al., 2012;
11 Brook et al., 2010). It is important to note, however, that these studies looked at particulate
matter from all sources, and that the premature deaths, morbidities, and associated costs incurred
from biomass combustion emissions would be proportional to their contribution to national PM
levels.
Wood Smoke
Wood is primarily composed of two polymers: cellulose (50-70% by weight) and
lignin (approximately 30% by weight; Naeher et al., 2007; Simoneit et al., 1998). These two
polymers are the primary components in many biomass fuels, although the ratios of composition
may vary depending on the source (e.g. wheat, grasses, cherry pits, etc.; Naeher et al., 2007).
Wood also contains small amounts of low-molecular-weight organic compounds and various
trace metals, which often vary based on the soil composition and the climate where the wood
grew (Naeher et al., 2007; Kleeman et al., 1999). Even if they are contaminate free, due to the
difficulty in mixing the fuel to air ratio when burning biomass fuels (opposed to liquid or gas
fuels) complete combustion rarely occurs (Naeher et al., 2007). In addition to the carbon
dioxide, nitrogen, and water that is released from complete combustion, incomplete combustion
produces various inorganic gases (carbon monoxide, ozone, nitrogen oxides), polycyclic
aromatic hydrocarbons (PAHs), benzene, aldehydes, free radicals and inhalable particulate
matter, all of which have been shown to negatively impact health (Naeher et al., 2007). In
addition to these pollutants, a number of compounds present in biomass smoke have been shown
to be toxic and/or carcinogenic to humans, including free radicals, hydrocarbons (PAHs,
benzene, and styrene), aldehydes, and phenols (Naeher et al., 2007; Leonard et al., 2000; Pryor,
1992; Schauer et al., 2001). These compounds begin to affect health when they enter the lungs
and bloodstream by adhering to particulate matter, and as such, previous studies have found
12 wood smoke PM to be more potent, or comparable, to cigarette smoke (Naeher et al., 2007;
Cupitt et al., 1994; Claxton et al., 2001; Danielsen et al., 2011: Boman et al., 2003). This
becomes a concern because studies looking at the impact of biomass combustion products on
indoor benzene and polycyclic aromatic hydrocarbons have found that indoor levels were
elevated by 29% and 400% respectively for homes that heated with biomass products (Gustafson
et al., 2007; Gustafson et al., 2008).
Particulate matter that is released during biomass fuel combustion peaks at 0.1-0.2 µm in
diameter, with a majority of all particulate matter less than 1 µm in diameter (Kleeman et al.,
1999; Hays et al., 2002). Due to size, these particles are not easily extracted from air via
gravitational settling and can, and have been documented, traveling hundreds of kilometers
(Echalar et al., 1995; Andrae et al., 1988). It is important to note, however, that PM emissions
are highly dependent on fuel type, moisture content of the fuel, and the burn conditions (Khalil &
Rasmussen, 2003; Guillen & Ibargoitia, 1999). Bad burn practices combined with poor quality
fuel can quickly add more carcinogenic/toxic compounds to the list, especially when
homeowners burn construction materials, packaging crates or household garbage. In fact,
“According to a study conducted by EPA, the New York State Department of Health (DOH), and
the New York State Department of Environmental Conservation (DEC), burning approximately
ten pounds of household trash in a burn barrel releases as much air pollution as a modern, wellcontrolled municipal waste incinerator burning 400,000 pounds of trash” (State of New York,
2008).
Mitigation
For individuals, communities, or industries that decide to use biomass combustion
products to provide heat or electricity, there are five methods that can be used to further reduce
13 PM and other harmful carcinogenic emissions, these include: 1) using high quality fuel when
using biomass combustion products; 2) using high-efficiency units and/or replacing non-EPA
qualified units with newer, EPA qualified models; 3) using proper burn practices and unit
maintenance procedures; 4) installing emission reduction equipment; and 5) using indoor
filtration systems to further reduce existing PM levels.
Fuel Quality
Using fuels that have low moisture content, are clean (free from bark and foliage), and
derived from hardwoods have all been shown to reduce PM, CO and carcinogenic organic
compound emissions. This can apply to units that burn whole logs, split wood, wood chips, or
pellets. Currently, there are no fuel standards set by the EPA for whole logs, split wood, wood
chips, or pellets (BERC 2011). Previous studies have found that low moisture content fuel
reduces PM and organic matter emissions, while hardwoods reduce CO and PM emissions, with
negligible effects on organic matter (Preto 2005). While there is sufficient evidence on the
connection between fuel quality and PM emissions, future research needs to be done to better
understand the impact on CO and carcinogenic organic compounds.
High-efficiency units
Using an EPA-qualified biomass combustion product, or replacing an existing unit with
an EPA-qualified product, is another method that can be used to reduce emissions from biomass
combustion products. Using outdoor wood boilers as an example, the average unqualified
outdoor wood boiler emits 161 grams of particulate matter an hour, with models generally
averaging between 100-300 grams per hour (NESCAUM 2006; EPA 2013b). In contrast, an
outdoor wood boiler that is EPA Phase 2 qualified emits less than 4 grams of particulate matter
an hour, with some models averaging less than 2 (EPA 2013b). This could be comparable to the
14 emissions of a single idling heavy-duty diesel engine, with particulate levels at about 2.59 grams
per hour (EPA 2013c).
A stove change-out program conducted in Libby, Montana further illustrates the impact
that non-qualified units have on PM emissions, and the reduction in emissions that could be
achieved by replacing these units with EPA Phase 2 qualified units. Replacing 1,200 nonqualified stoves in Libby, Montana with EPA Phase 2 units, the community observed a 50%
reduction in outdoor ambient PM emissions for residential wood stoves, a 20% overall reduction
in outdoor ambient PM levels, and a 71% reduction in indoor PM2.5 levels (Ward et al., 2008;
Bergauff et al., 2009).
While the federal government has imposed some regulations on the sales and installations
of specific types (indoor residential) of biomass combustion products, currently there are no
regulations at the federal level that dictate the type of biomass combustion product that can be in
use.
Proper Burn Practices and Maintenance Procedures
Using proper burn practices and maintenance procedures on existing biomass combustion
products has also been associated with increased thermal efficiency and lower emission levels
(BERC 2011). However, while this statement is commonly accepted in the biomass industry, no
published research has been conducted to support this claim.
Emission Reduction Equipment
There are currently six types of emission reduction equipment that can be used to reduce
biomass combustion emissions, these include: catalysts, single cyclones, multi-cyclones, core
separator, bag houses (filter fabrics), and electrostatic precipitators. It is important to note,
15 however, that the latter five are mainly employed on larger commercial industrial units, and are
not used in residential units (BERC 2011).
Catalysts are unique from other biomass emission reduction technologies as they are the
only emission reduction technology that reduces CO and VOCs (volatile organic compounds) in
addition to reducing PM emissions. Providing a reactive surface that biomass emissions pass
over, CO, VOCs, and other unburned hydrocarbons and PM are further reduced to carbon
dioxide and water. Often, in order to become reactive, these catalysts need to get up to
temperature before they become effective, and as such, catalysts are often placed into two
categories, active or passive. Passive catalysts use the heat from the biomass combustion
emissions to heat the catalyst. Due to this process, these units can often take an extended period
of time to come up to temperature, and therefore have uncontrolled emissions during the start up
and refueling period. Active catalysts use electric or propane heaters to heat the catalyst to its
activation temperature, and therefore have continuous control over biomass emission levels. Due
to the nature of catalysts, they are very effective at reducing CO and VOC emissions, with
previous studies documenting catalysts reduction in CO and VOC levels of 95% and 80%
respectively (Ozil et al., 2009).
Single and multi-cyclones use centrifugal force to remove particulate matter from
biomass combustion emissions. As the air spins into the top of a cyclone chamber, the
gravitational force on the particulate matter causes it to settle and eventually drop out of the
cyclone body into a collection device located below while the “clean” air escapes through the top
of the chamber (BERC 2011). A single cyclone simply uses one cyclone body, while a multiple
cyclone unit uses multiple smaller cyclones to improve efficiency (BERC 2011). A single
16 cyclone can reduce PM10 emissions by 50%, and PM2.5 emissions by 5% (BERC 2011). Multicyclone units can reduce PM10 emissions by 75%, and PM2.5 emissions by 10% (BERC 2011).
A core separator system works to reduce particulate matter emissions from biomass
combustion products in a near identical way to that of the single-cyclone system. In a core
separator system biomass combustion emissions are cycled through a cyclone chamber using a
re-circulatory fan. Opposed to the single/multiple cyclone system, in the core separator system
the emissions are re-circulated through the cyclone multiple times before the “clean” emissions
are released (BERC 2011). Able to pass emissions through the cyclone multiple times, core
separators can reduce PM10 emissions by 29-56%, and PM2.5 emissions by 72-94% (BERC
2011). It is important to note, however, that these units are currently not available for
commercial purchase/use.
In bag houses, biomass combustion emissions are passed through fabric filters to remove
PM emissions. As these filters work best when not overloaded with particulate matter, these
units are often run in sequence with cyclones (which are efficient at removing course PM) prior
to passing the emissions through filter fabrics, which are much more effective at removing fine
PM (BERC 2011). While bag houses can be very effective, they are also known to catch fire
when hot embers come in contact with the fabric filters (BERC 2011). Due to the cyclone and
fabric filter however, bag houses are very efficient at removing PM emissions and can reduce
both PM10 and PM2.5 emissions by 99% (BERC 2011).
An electrostatic precipitator (ESP) reduces PM emissions by charging the emissions from
biomass combustion products (giving PM a positive charge) and then collecting it on a
negatively charged plate (BERC 2011). Plates are then cleaned periodically via hammers or
vibrations to dispose of collected PM. ESPs are very effective at removing PM emissions
17 (without the fire risk of bag houses) and can reduce PM10 emissions by 95% and PM2.5 emissions
by 90% (BERC 2011).
Indoor Filtration
In communities or homes where PM levels are high, another mechanism that can be used
to lower indoor and personal PM exposure is through indoor filtration devices. One study,
conducted by Allen et al. found that when a HEPA filter was placed in the main activity room
and bedroom, personal PM exposures were reduced by 60% (Allen et al., 2011).
Future Work
This paper has provided a brief overview of particulate matter, biomass combustion, wood
smoke and health. Through writing this paper, numerous topical areas have been uncovered
where future research should be conducted, including:
 Studying the impact of indoor or outdoor biomass combustion products on
indoor/personal PM levels. While extensive research has been done in developing
countries, little research has been done in developed countries evaluating this impact.
 Studying the carcinogenicity/toxicity of the chemical compounds present in wood smoke
when exposed via wood smoke. While the carcinogenic/toxic components of wood
smoke have been proven to cause cancer, both in human and animal models, very little
research has been done to study the health effects and levels of exposure of these
compounds when exposed via wood smoke.
 Studying the impact that fuel quality and moisture has on CO, PM, and carcinogenic
organic compound emissions from biomass combustion.
 Studying the impact of burn practices and proper maintenance procedures on biomass
combustion emissions.
18  Studying the reductions in CO, VOCs, and PM emissions that could be achieved through
the use of a catalyst on biomass combustion units.
Acknowledgements
The author would like to express sincere thanks to ClearStak LLC for providing the funding to
support the development of the initial and future versions of this paper.
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Anderson, J. O., Thundiyil, J. G., & Stolbach, A. (2012). Clearing the air: a review of the effects
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