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Air pollution from biomass energy (updated April 2011) 

Despite the frequent depiction of biomass as “clean” energy, data from air permit applications and real 

smokestack tests demonstrate quite clearly that biomass is a heavily polluting technology. 

Burning wood and other biological materials for energy emits as much or more pollution than burning 

fossil fuels, including coal. Emissions are function of the fuel type, combustion temperature, and pollution 

controls, but in PFPI’s analysis of air pollution permits in 7 states we have found that biomass burners are 

always more polluting than natural gas and are similar to coal - admittedly better for some pollutants like 

sulfur and mercury, but the same or worse for particulates and nitrogen oxides. Being similar to coal

hardly qualifies as clean, green energy. 

Biomass electricity generation facilities are major air polluters, and in many cases will significantly worsen 

air quality in the communities and regions where they are constructed. Yet in most cases biomass gets a 

break because it is (inaccurately) considered renewable and carbon neutral. 

The We Energies facility in Rothschild, Wisconsin is an example of regulators allowing a heavily polluting 

biomass facility to proceed precisely because it is classified as renewable and counts toward the state’s 

renewable energy goals. According to the facility’s air permit, the new biomass burner, located at the

Domtar paper mill, will be a huge air polluter. It will almost certainly throw the region into violation of air 

pollution health standards for particulate matter, which the US EPA considers a lethal form of air pollution 

that causes ten of thousands of premature deaths across the country each year and increases the 

incidence of asthma attacks in children; and it will emit 6 times as much carbon per unit of electricity 

generated as a natural gas burner being constructed on the same site. State regulators could have 

required cleaner burning fuels at the plant, but declined to do so specifically because the plant is 

producing “renewable” energy. 

Sanctioning and subsidizing major new sources of potentially lethal air pollution is not what anyone had in 

mind when establishing renewable energy standards. Regulators should take a clear-eyed, fact-based 

approach to evaluating whether or not these facilities should operate given the significant air pollution that 

they cause. In our view, biomass burners should not be allowed to operate until they can show that they 

are dramatically cleaner then all fossil fuel alternatives, if they are to qualify as renewable energy under 

state policies. 

What kind of pollution does a biomass burner emit? 

Burning biomass emits large amounts of pollutants, just like burning other solid fuels such as coal. 

Burning organic material emits particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), 

sulfur dioxide (SO2), lead, mercury, and other hazardous air pollutants (HAPs). 

Hazardous air pollutants are a group of 187 toxics that according to EPA “are known or suspected to 

cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse 

environmental effects”. EPA has recently released the newest National Air Toxics Assessment, which 

characterizes emissions and ambient air concentrations of toxics around the country. 

The HAPs emitted in the greatest quantities by burning biomass include the organic HAPs styrene, 

acrolein, and formaldehyde, and the acid gases hydrofluoric acid and hydrochloric acid,. Biomass burners 

commonly emit ten tons or more of the acid gases and from one to five tons of organics each year. Even

“clean wood” – that is, forestry-derived wood, as opposed to construction and demolition debris – emits 

these chemicals when burned. Burning clean wood also emits non-negligible amounts of heavy metals. 

Burning “urban wood” – a friendly term for construction and demolition debris (CDD) – significantly 

increases emissions of arsenic, chromium, copper, lead, and mercury, as well as dioxins/furans and 
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pentachlorophenol (PCPs). Biomass developers sometimes claim that sorting out the contaminated wood 

from CDD produces a “clean” and safe fuel stream, but it is virtually impossible (and not cost effective) to 

remove the contaminated wood using visual inspection and hand sorting. Even one or two percent 

contaminated wood can lead to significant emissions of metals when this material is burned (see a letter

documenting the inadequacy of CDD sorting for a proposed CDD-burner in Massachusetts, and a letter 

from the MA Department of Environmental Health expressing concerns about emissions of metals and 

other air toxics in the environmental justice community of Springfield, MA, where childhood asthma rates 

and incidence of high blood lead levels are already twice the State average). 

How much pollution do biomass-burning facilities emit? 

Most biomass plants do not use the most effective pollution controls, and small-scale biomass burners,

like those being installed to provide heat to schools around the country, typically only have minimal 

controls. Utility-scale biomass plants emit tens to hundreds of tons of particulates, nitrogen oxides, carbon 

monoxide, and and hazardous air pollutants each year. 

Emissions are typically expressed in air permits as pounds of pollution per million btu of heat input (as 

fuel). The problem with this approach is that it hides differences in efficiency that exist between facilities. 

Converting these rates so they are expressed in terms of emissions per unit energy delivered to the grid 

is a more accurate way of evaluating the impact of different technologies and fuels. 

To give an idea of how much pollution a biomass plant can produce, here are emissions numbers from 

the air permit and application documents for the proposed 100 MW Gainesville Renewable Energy Center 

(GREC) in Florida, contrasted with air permit numbers from the much larger Pioneer Valley Energy Center 

(PVEC), a 431 MW gas and diesel plant proposed in Westfield, Massachusetts. The emissions rate for 

the biomass plant far exceeds that for the gas plant for criteria air pollutants, HAPs, and carbon dioxide. 

Yet biomass proponents insist on calling biomass a “clean” fuel. 

Here are some more data on pollution emissions, showing how different the emissions are when the 

same burner is firing different fuels. The following table is from the air permit application for the Hu Honua 

facility in Hawaii, an old coal burner that is being retrofitted to burn wood and biodiesel. Pollution

emissions from the boiler (here expressed as pounds per million btu) are significantly greater when 

biomass is used as a fuel: 

The 100 MW Gainesville Renewable 

Energy biomass plant will emit 

dramatically more pollution than a 431 

MW gas/diesel plant in Massachusetts, 

both as total tons, and as lb per MWh

GREC: 100 

MW biomass: 

tons per year

GREC 

biomass 

lb/MWh

PVEC: 431 MW 

nat gas/diesel: 

tons per year

PVEC: nat 

gas/diesel 

lb/ MWh

GREC rate as % 

PVEC rate

Nitrogen oxides 416.4 0.95 91.9 0.05 1953%

Carbon monoxide 713.8 1.63 59 0.03 5214%

Particulate matter 249.8 0.57 49.1 0.03 2193%

Sulfur dioxide 243.9 0.56 16.7 0.01 6295%

Volatile organic compounds 77.3 0.18 23.8 0.01 1400%

Hazardous air pollutants 24.7 0.06 5.1 0.003 2087%

Carbon dioxide 1,232,225 2,813 1,432,825 759 371%
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Emissions data for school-sized boilers also highlight the difference between biomass and other fuels.

The Wyalusing School District in Pennsylvania applied for air permits for a new biomass burner, and a 

new oil burner. Emissions rates for the biomass burner are higher for PM, NOx, and CO, but are lower for 

VOCs and SO2 (differences in the total tons emitted are to some extent also a function of the different 

amounts of time the burners are projected to be used.). All rates are in units of lb/mmbtu. 

Control of particulate matter 

Particulate matter emissions are implicated in a wide range of health impacts, from asthma and heart 

disease to diabetes. Even when the most sophisticated emissions controls are used, biomass burning 

produces large amounts of the fine particulate matter that penetrates deeply into the lungs. There are a 

number of technologies for reducing emissions of filterable particulate matter, but three main technologies 

are often used with biomass burners. None is truly effective at removing fine particulates. 

Cyclone and multicyclone systems rely on centrifugal force to spin particulates out of the flue gas. 

Cyclonic systems are not effective at removing the fine particulate matter that has the greatest impact on 

air quality and health, although according to EPA, some high efficiency systems show removal of 60 to 

95% for PM10 and 20 to 70% for PM2.5. Cyclone systems are often found as the sole means of PM control 

at small-scale burners like those installed in schools around the country. Emissions data from the 

Wyalusing air permit, above, show that a typical school burner may emit around 9 tons of particulate 

Wyalusing Area School District - emissions from new biomass and oil burners

PM rate PM tons NOx rate NOx tons CO rate CO tons VOC rate VOC tons SO2 rate SO2 tons

Oil burner 0.03 0.29 0.12 1.18 0.04 0.39 0.025 0.25 0.21 2.06

Wood burner 0.22 8.68 0.182 7.18 0.163 6.48 0.004 0.16 0.002 0.08
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matter a year. These emissions occur from low stacks and impinge directly on children in playgrounds 

and as they sit in class. 

Electrostatic precipitators (ESPs) use an electric field to remove particles from the flue stream. They can 

remove up to 99% of fine particles (PM2.5) from the flue gas, although their efficacy in removing ultrafine 

particles is not well quantified. ESPs are expensive and are not typically installed in building-scale

biomass burners. 

Additionally, with all these control technologies, we are talking about removal of filterable particulate 

matter, which is just one component of total particulate matter. The other component is known as 

“condensable” particulate matter, and it consists of the fine and ultra-fine particles derived from sulfur, 

nitrogen, and VOC emissions that condense in the atmosphere after the flue gas has left the stack. 

Because the actual formation of condensable particulate matter depends both on emissions and 

atmospheric chemistry, it is not well characterized, therefore most air permitting agencies make some 

assumption about the ratio of condensable to filterable particulate matter when they are writing a permit 

for the amount of total particulate matter (filterable plus condensable) emitted by a facility. Such 

assumptions may or may not be well-justified. 

Fabric filters or baghouses are generally considered the most effective means of emissions control for

filterable particulates. They can show control efficiencies upwards of 99%. They are installed at some

mid-sized facilities and many utility-scale facilities. 

The amount of particulate matter emitted from a biomass burner is highly sensitive to small differences in 

control efficiency. The following table shows how much filterable PM10 is emitted in four different 

scenarios. Note that the first scenario combusts a much smaller amount of wood than the other three – 

this is meant to represent the operation, for instance, of a biomass burner at a mill that is generating 

power and heat for its own operation. Despite the relatively small amount of wood burned, the average

control efficiency of 80% for the multiclone system means that PM emissions are quite high. 

The three other scenarios (2-4) show a larger amount of wood, such as would be burned at a utility-scale 

biomass plant supplying power to the grid, and three different levels of control efficiency. Even a few 

tenths of a percent of control efficiency make a large difference to the total tons of PM emitted. This is 

also relevant to control of heavy metals, which are generally assumed to be emitted as a component of 

particulate matter, with the exception of mercury, which is emitted as a vapor. 

Emissions from small-scale biomass burning compared to wood stove emissions 

Biomass proponents will sometimes claim that biomass burners “emit less pollution than a woodstove”. 

For well controlled facilities, per unit wood burned, this is true, because baghouses and other pollution 

control equipment reduce the amount of pollution emitted. However, the sheer amount of material burned

Control of filterable particulate matter

Scenario

Control 

technology

control 

efficiency

uncontrolled 

PM10 

(lb/mmbtu) tons wood

tons PM 

(uncontrolled)

PM rate 

(lb/mmbtu)

tons PM 

emitted

1 Multiclone 80.0% 6.5 26,000 799 1.3 160

2 ESP 99.0% 6.5 400,000 12,298 0.065 123

3 Baghouse 99.5% 6.5 400,000 12,298 0.0325 61

4 Baghouse 99.9% 6.5 400,000 12,298 0.0065 12
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in a utility-scale facility or even at a medium-sized sawmill means that pollution emissions massively

exceed those from a residential wood-burner. And the emissions are no less harmful. The size distribution 

of the particulate matter that escapes control by a baghouse or ESP is shifted toward the smallest size 

fractions – and in the case of particulates (not to mention all the other pollutants) what you can’t see can 

definately can hurt you. 

But what about a school-sized facility, compared to a woodstove? Estimates of the amount of particulate 

matter emitted by a residential woodstove vary by a factor of ten or more, but assuming an average PM 

emission rate of 30 grams per hour (a value between old woodstoves and EPA-certified woodstoves), and 

assuming 6 months of stove operation at 18 hours per day, the average woodstove emits about 214 lb of 

particulate matter over the heating season. Assuming 6 months of operation for a school sized boiler of 

about 4 mmbtu, such a facility might emit around 1.9 tons of particulate matter. This would then be about 

the equivalent of PM emissions from about 18 residential woodstoves. 

How do emissions from biomass plants compare with coal plants? 

Different plants have different emissions rates depending the fuel burned, control equipment installed, 

and how well the facility is operated. The EPA “BACT Clearinghouse” (BACT means “Best Available 

Control Technology”) contains permitted emission rates for fossil fuel and biomass plants around the 

country. While the database is not comprehensive, and does not necessarily show the best controlled 

plants, it provides a representative sample of some of the lower emitting plants around the country. The 

following table shows a range of emission rates for existing coal plants and biomass plants from the 

BACT Clearinghouse, as well as the Ryegate biomass plant in Vermont, a recently re-permitted existing 

plant, and rates from a variety of permits for proposed biomass plants around the country. 

The data show that emission rates for NOx at some coal plants are lower than at many biomass plants. If 

the typical difference in plant efficiency were taken into account and the rates expressed on a per MWh 

basis, instead of a heat input basis, the difference would be even greater. Similarly, there is a high degree 

of overlap for CO and PM emission rates between coal plants and biomass plants. Sulfur dioxide (SO2, or 

SOx) is the pollutant where emission rates are clearly higher for coal than biomass. The BACT 

Clearinghouse does not include data on VOC emissions. 

Some coal plants achieve lower emissions rates than are allowed in their permits. For instance, the 

Mount Tom coal plant in Holyoke, MA, has turned in stack test data that indicate the plant’s SO2 emission 

rate is 0.066 lb/mmbtu, lower than any rate reported in the BACT clearinghouse database. The data also

indicate a total PM10 emission rate of 0.0059 lb/mmbtu, meaning that yearly emissions of PM10 from this 

147 MW facility are around 39 tons per year if the facility operates continuously. In contrast, the 35 MW 

Palmer Renewable Energy biomass plant to be built in nearby Springfield, MA, will have a total PM10 

emission rate of 0.019 lb/mmbtu and will emit 42.4 tons of PM10 per year. 

Does co-firing biomass reduce emissions? 

Co-firing biomass is sometimes seen as a way to reduce emissions at coal plants, particularly of sulfur 

dioxide, because wood generally has a lower sulfur content than coal (an exception is construction and

boilers > 250 mmbtu/hr, emissions as lb/mmbtu of heat input

Existing coal Existing biomass Ryegate biomass Proposed biomass

NOx 0.07 (several) 0.065, 0.1 - 0.15 0.15 0.06 - 0.15

CO 0.1, 0.13, 0.135 0.1, 0.19, 0.24, 0.3 0.3 0.0365 - 0.176

PM10 fil 0.01, 0.012 0.02, 0.025, 0.03 0.017 0.008 - 0.015

SOx 0.1, 0.14, 0.245 0.02 0.019 0.012 - 0.042
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demolition debris, which can have relatively high sulfur content probably due in some part to 

contamination by gypsum wallboard waste). 

While replacing a significant amount of coal with wood would reduce sulfur emissions, the effect on other 

pollutants is not straightforward. Test-firing data from the Killen coal plant in Ohio, which proposes to cofire 5% wood by heat content (amounting to over 8% by mass) shows that adding even this small amount 

of wood to the fuel stream produces dramatic increases in emissions of carbon monoxide and hazardous 

air pollutants. 

The following data are from the Killen plant’s technical support document for the air permit application to 

co-fire biomass. Metals emissions show some small increases and decreases with addition of biomass, 

and there are small percentage decreases in emissions of hydrochloric acid and hydrofluoric acid, but the 

key thing to notice is that replacing 5% of the boiler’s heat input with biomass produces no improvement 

in criteria pollutant emissions with the exception of a small decrease in lead emissions. It does, however 

produce large percentage increases in carbon monoxide, volatile organic compounds (VOCs), and certain 

organic hazardous air pollutants (HAPs). 

“PTE” means “potential to emit”, which standardizes emissions by assuming the boiler operates at full 

capacity 365 days of the year. All emissions are expressed as tons per year (“tpy”). 
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The Killen plant will co-fire about 180,000 tons of wood per year, or the equivalent of the wood that could 

be produced by clearcutting about 2,050 acres of Ohio’s forests per year (we use U.S. Forest Service 

data to estimate standing biomass). Increasing the amount of wood co-fired to a level that would actually 

decrease sulfur emissions would require significantly increasing forest harvesting, and would meanwhile 

have unacceptably large effects on emissions of other pollutants. Co-firing biomass should not be allowed 

as a way for coal plants to avoid installing modern pollution control equipment, which is vastly more 

effective at reducing sulfur emissions than changes in fuel. 

Biomass and the Clean Air Act 

Large-scale biomass burners are subject to Clean Air Act regulation and permitting like other emitters, 

with one crucial difference. The Clean Air Act requires “Prevention of Significant Deterioration” (PSD) 

review for air quality when a new “major source” facility is built or when an existing facility undergoes 

major modification in an area that is either classed as in attainment, or unclassifiable, with regard to the 

National Ambient Air Quality Standards (NAAQS). PSD review requires installation of the Best Available 

Control Technology (BACT, a standard that takes into consideration the cost of air pollution controls, and 

allows rejection of some controls as too expensive), air quality analysis, an additional impacts analysis, 

and public involvement. However, while the threshold for triggering PSD review for a fossil-fueled boiler 

250 mmbtu/hr or greater is emission of 100 tons of a criteria pollutant, the threshold for triggering PSD 

review for a biomass burning facility is 250 tons. This means that a facility burning biomass can emit two 

and a half times the amount of pollution that a fossil-fueled facility emits before it is subjected to a similar 

level of scrutiny and emissions control. 

Biomass, Hazardous Air Pollutants, and EPA’s “boiler rule” 

To reduce the amount of hazardous air pollutants emitted by commercial and industrial boilers, EPA sets 

limits for certain pollutants under the “boiler rule”, which is part of the Clean Air Act. The boiler rule is 

especially significant for biomass burners because although the boiler rule regulates fossil-fueled boilers 

only up to 25 MW in size, it regulates all biomass boilers, no matter how large. 

The boiler rule sets the maximum allowable emission limits for just five pollutants, although there are 187 

different HAPs recognized by EPA. Setting emissions limits for each one would be difficult, so instead, 

EPA regulates the majority of pollutants by dividing them into classes and using proxies to estimate how 

well their emissions are controlled. Under the boiler rule, particulate matter (PM) serves as a proxy for 

metallic HAPs like arsenic and lead, and carbon monoxide (CO) is regulated as a proxy for organic HAPs

like formaldehyde and acrolein. The boiler rule regulates dioxins/furans, mercury, and hydrochloric acid 

(HCl) directly, with HCl also acting as a proxy for other acid gases (like hydrogen fluoride). 
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To control emissions of these pollutants, EPA sets maximum emissions rates for different kinds of boilers 

and different fuels. These emission rates are based on the “best performing” (lowest emitting) units that 

already exist. To set emissions rates for existing boilers, EPA essentially averages the best performing 

12% of boilers, using their emission rates as the standard that all existing units are supposed to achieve. 

For new as-yet-unbuilt boilers, EPA expects those to achieve the same emission rate as the single best

performer (lowest emitter) that already exists. These standards are referred to as Maximum Achievable

Control Technology (MACT), and are set for coal, biomass, gas, and other liquid fuels boilers. 

EPA further identifies two categories of emission sources under the boiler rule – “major” and “area” 

sources. A major source is one which emits 25 tons or more of total HAPs, and 10 tons or more of any 

single HAP (for biomass, the HAP usually emitted in the greatest quantities is hydrochloric acid, or HCl). 

An “area” source is one which emits HAPs below these thresholds. 

Since the emission rules for major sources are considerably more stringent than for area sources, there is 

a great incentive for facilities to characterize themselves as area sources. Below is a summary of the

allowable emission rates for major and area sources. Emission rates for biomass under the major source

rule are the same as for coal, except for emission rates of carbon monoxide and dioxins/furans, which are 

generally higher than for coal. 

“Boiler rule” emission rates for major sources. 

Subcategory 

Particulate 

Matter

Hydrogen 

Chloride

Mercury

(Hg) 

Carbon Monoxide 

(ppm @3%oxygen) 

Dioxin/ Furan 

(TEQ) (ng/dscm) 

Existing –CoalStoker 0.039 0.035 4.6E-06 270 0.003

Existing -Coal Fluidized Bed 0.039 0.035 4.6E-06 82 0.002

Existing –Pulverized Coal 0.039 0.035 4.6E-06 160 0.004

Existing –Biomass Stoker/other 0.039 0.035 4.6E-06 490 0.005

Existing -Biomass Fluidized Bed 0.039 0.035 4.6E-06 430 0.02

Existing –Biomass Dutch Oven/Suspension Burner 0.039 0.035 4.6E-06 470 0.2

Existing –Biomass Fuel Cells 0.039 0.035 4.6E-06 690 4

Existing –Biomass Suspension/Grate 0.039 0.035 4.6E-06 3,500 0.2

Existing –Liquid 0.0075 0.00033 3.5E-06 10 4

Existing – Gas2 (OtherProcess Gases) 0.043 0.0017 1.3E-05 9 0.08

Existing –non-continental liquid 0.0075 0.0003 7.8E-07 160 4

New –Coal Stoker 0.0011 0.0022 3.5E-06 6 0.003

New - Coal Fluidized Bed 0.0011 0.0022 3.5E-06 18 0.002

New – Pulverized Coal 0.0011 0.0022 3.5E-06 12 0.003

New – Biomass Stoker 0.0011 0.0022 3.5E-06 160 0.005

New - Biomass Fluidized Bed 0.0011 0.0022 3.5E-06 260 0.02

New – Biomass Dutch Oven/Suspension Burner 0.0011 0.0022 3.5E-06 470 0.2

New – Biomass Fuel Cells 0.0011 0.0022 3.5E-06 470 0.003

New - Biomass Suspension/Grate 0.0011 0.0022 3.5E-06 1,500 0.2

New – Liquid 0.0013 0.0031 2.1E-07 3 0.002

New – Gas 2 (Other ProcessGases) 0.0067 0.0017 7.9E-06 3 0.08

New – non-continental liquid 0.0013 0.0032 7.8E-07 51 0.002
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“Boiler rule” emission rates for “area” sources. 

From the heat input levels set in the area source rule, one can see that EPA had in mind regulating 

relatively small boilers. A 10 mmbtu/hr boiler is representative of the size being installed in some school 

districts, capable of heating more than one building. A 30 mmbtu boiler is the size used by a small 

sawmill. However, many of the extremely large boilers being built currently are classified as “area” 

sources. For instance, the Gainesville Renewable Energy Center, a 116 MW (gross; 100 MW net) 

biomass burner with a 1,359 mmbtu boiler, is considered to be an “area” source, because the project 

claims it will emit less than 25 tons of hazardous air pollutants (the exact value in the permit is 24.7 tons 

of HAPs). This massive project, which will burn well over a million tons of wood a year, will therefore not 

be held to the stricter standards of the “major” source boiler rule. 

An important thing to notice about the area source rule is that while EPA set limits for mercury and carbon 

monoxide for existing and new coal boilers, to which it adds the regulation of PM for new coal boilers, 

new biomass boilers are only required to meet PM standards, and there are no standards at all for 

existing biomass boilers. 

Information on air pollutants 

Nitrogen dioxide (NO2) 

Nitrogen dioxide (NO2) is the indicator species for the NOx group of gases, which includes nitrous acid 

and nitric acid. It primarily forms when fuels are burned at high temperatures. These acidic gases directly 

impact respiratory health, and also contribute to formation of ozone and condensable particulate matter. 

Nationwide, the majority of NO2 is from the transportation sector, but utilities and other sources of 

combustion account for about 34% of total emissions. 

As of January 2010, EPA set a new 1-hour standard for NO2 of 100 ppb in ambient air, and retained the 

annual average pollution standard of 53 ppb. 

Ozone 

Subcategory Heat Input (mmbtu/hr) Pollutants Emission limit

Coal

Existing coal-fired boiler >= 10 Mercury 0.0000048 lb/mmbtu

Existing coal-fired boiler >= 10 Carbon monoxide 400 ppm by vol @3% O2

New coal-fired boiler >= 30 Particulate matter 0.03 lb/mmbtu

New coal-fired boiler >= 30 Mercury 0.0000048 lb/mmbtu

New coal-fired boiler >= 30 Carbon monoxide 400 ppm by vol @3% O2

New coal-fired boiler >= 10 and < 30 Particulate matter 0.42 lb/mmbtu

New coal-fired boiler >= 10 and < 30 Mercury 0.0000048 lb/mmbtu

New coal-fired boiler >= 10 and < 30 Carbon monoxide 400 ppm by vol @3% O2

Biomass

New biomass-fired boiler >= 30 Particulate matter 0.03 lb/mmbtu

New biomass-fired boiler >=10 and < 30 Particulate matter 0.07 lb/mmbtu

Oil

New oil-fired burner >= 30 Mercury 0.03 lb/mmbtu

New oil-fired burner >= 10 and < 30 Carbon monoxide 0.03 lb/mmbtu
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A principle component of smog, ground level ozone is formed when nitrogen oxides (NOx), volatile 

organic compounds (VOCs), carbon monoxide (CO), and methane react, energized by UV light. The main 

sources of NOx and VOCs are industrial facilities, electric utilities, motor vehicle exhaust, gasoline vapors, 

and chemical solvents. As a highly reactive oxidant gas, ozone aggravates the airways, causing 

respiratory distress and exacerbating asthma. It also damages vegetation and is increasingly recognized 

as a threat to forest health. 

EPA has proposed revising its eight-hour standard for ozone from 0.075 ppm to 0.06 – 0.07 ppm, 

acknowledging that the ozone standards set in 2008 were not as protective as recommended by EPA’s 

panel of science advisors, the Clean Air Scientific Advisory Committee (CASAC). EPA has also proposed 

a new “seasonal secondary standard” for ozone exposure that represents cumulative exposure during 

peak ozone season. 

Sulfur dioxide (SO2) 

Sulfur dioxide (SO2) exposure causes breathing difficulty for people with asthma, and is also implicated in 

regional haze and acid rain formation. A recent EPA risk assessment for SO2 concludes that definite 

health risks to asthmatics occur at concentrations significantly lower than the current 24-hour health

standard for SO2. The document further notes that “over 20 million people in the U.S. have asthma, and 

therefore, exposure to SO2 likely represents a significant health issue.” The main sources of SO2 are 

fossil fuel combustion at power plants and industrial facilities. Along with its direct effects, SO2 also 

contributes to the formation of fine particulate matter. EPA concluded that a new SO2 standard with a 1-

hour averaging time would be more protective. As of June 2, 2010, EPA strengthened the NAAQS for 

SO2 by adding a 1-hour standard set at 75 ppb. 

Particulate matter (PM) 

Fine particle emissions arise from both direct ash emissions from combustion at energy plants, but also

form from emissions of sulfur dioxide, nitrogen oxides, ammonia, and volatile organic compounds. 

Particulate air pollution has long been known to be associated with increased cardiopulmonary 

symptoms, asthma attacks, days lost from work due to respiratory disease, emergency room visits, 

hospitalization rates, and mortality. Two size classes are recognized in regulatory schemes: PM10 and 

PM2.5, with the numeric value referring to the particle size in microns (a micron is one millionth of a 

meter). There is no current health standard for PM10; EPA’s 24-hour and annual exposure standards for 

PM2.5 are 35 micrograms per cubic meter (μg/m3

) and 15 μg/m3. EPA’s most recent risk assessment for 

PM acknowledges that the current standards are insufficiently protective and indicates that the agency

will be lowering the National Ambient Air Quality Standards (NAAQS) for PM2.5 once more. 

The classes of particulate matter classed as “black carbon” are implicated in a recent study as having up 

to 60% of the climate warming effect of CO2, by both creating “brown clouds” and darkening and thus 

increasing the heat absorption of snow and ice in polar regions. Controlling soot emissions and thus 

lessening albedo effects may thus be an even faster way to mitigate sea ice melting than controlling 

greenhouse gas emissions. A recent UN report found that controlling black carbon emissions and ozone 

could dramatically reduce global warming and improve human health. 

Lead 

Lead exposure primarily occurs from paint that has not been remediated. Lead exposure in children is 

linked to a variety of developmental and neurological problems. A recent study concluded that 

“long-term trends in population exposure to gasoline lead were found to be remarkably consistent with 

subsequent changes in violent crime and unwed pregnancy. Long-term trends in paint and gasoline lead 

exposure are also strongly associated with subsequent trends in murder rates going back to 1900. The 

findings on violent crime and unwed pregnancy are consistent with published data describing the 

relationship between IQ and social behavior. The findings with respect to violent crime are also consistent 

with studies indicating that children with higher bone lead tend to display more aggressive and delinquent 
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behavior. This analysis demonstrates that widespread exposure to lead is likely to have profound 

implications for a wide array of socially undesirable outcomes.” 

EPA recently dropped the NAAQS for lead from 1.5 μg/m3 to 0.15 μg/m3. 

Carbon monoxide (CO) 

Carbon monoxide is a product of incomplete combustion that when inhaled, interferes with oxygen 

absorption in the blood. Emissions of CO from biomass boilers generally increase with fuel moisture; 

“good combustion practices” are frequently cited as the best control for CO emissions. Carbon monoxide

can accumulate in closed spaces and could be a problem in the vicinity of improperly ventilated 

combustion sources. Carbon monoxide is treated under EPA’s “boiler rule” as a proxy for certain organic 

toxics that are assumed to increase as CO emissions increase. 

Hazardous Air Pollutants (HAPs) 

Hazardous air pollutants (HAPs) is the group name for 187 compounds which are known to have highly 

harmful health or environmental effects. The list includes metals like chromium, lead, and mercury, as

well as compounds like dioxins (products of combustion that are widely considered to be among the most

toxic chemicals known), benzene (a constituent of gasoline) and formaldehyde. EPA has classified two 

HAPs as human carcinogens (arsenic and the hexavalent form of chromium, CrVI) and four as probable 

human carcinogens (cadmium, lead, dioxins/furans, and nickel). All of these HAPs, as well as others, can 

be emitted in significant amounts by biomass energy facilities that burn “urban wood” as fuel, which 

contains lead-painted wood, wood treated with copper chromium arsenate, and non-wood materials that 

exacerbate dioxin/furan formation. Monitoring for these pollutants is rare, but emission levels can be high 

in the vicinity of specific emitters. 

Arsenic 

Considered a human carcinogen by EPA, arsenic is highly toxic, and is a principle component of copperchromium-arsenate (CCA) mixture that was used for pressure-treating lumber. Facilities that proposed to 

burn waste wood generally rely on visual sorting techniques to remove arsenic-containing pressuretreated wood from the CDD that it burns. However, such detection can be difficult, as noted by the 

Massachusetts Department of Environmental Protection website, which states 

“You can usually recognize pressure treated wood by its greenish tint, especially on the cut end, and 

staple-sized slits that line the wood. However, the greenish tint fades with time, and not all pressure 

treated wood has the slits”. 

Hexavalent chromium 

Chromium is also a constituent of pressure-treated wood, and is toxic, particularly in the hexavalent form 

(CR VI). EPA’s website states: “The respiratory tract is the major target organ for chromium (VI) toxicity, 

for acute (short-term) and chronic (long-term) inhalation exposures. Shortness of breath, coughing, and 

wheezing were reported from a case of acute exposure to chromium (VI), while perforations and 

ulcerations of the septum, bronchitis, decreased pulmonary function, pneumonia, and other respiratory 

effects have been noted from chronic exposure. Human studies have clearly established that inhaled 

chromium (VI) is a human carcinogen, resulting in an increased risk of lung cancer. Animal studies have 

shown hexavalent chromium to cause lung tumors via inhalation exposure.” EPA’s conversion constant

for the proportion of total chromium from biomass burning that is emitted in the hexavalent form is 56%. 

Mercury 

Mercury is a significant and dangerous contaminant that damages neurological development and other 

organ functions. It accumulates up food chains, presenting the greatest threat to humans and fish-eating 

birds like loons. Mercury is transported in the atmosphere but a significant amount from a point source 

can be deposited nearby, contaminating soils and water bodies. Biomass burning can emit surprisingly 

high amounts of mercury; for instance, the 21.5 MW Hu Honua facility planned in Hawaii would emit

about 10 lb of mercury per year. This emissions rate is about 0.053 lb/kWh, more than 21 times the 
Partnership for Policy Integrity 

info@pfpi.net 

0.0025 lb/kWh emissions rate at the Mount Tom coal plant in Holyoke, Massachusetts. To be sure, the 

rate at the coal plant is this low because the facility has installed expensive emissions control equipment 

– equipment that biomass developers refuse to install because it is not “cost effective”. 

Dioxins/Furans 

Dioxins/furans are “persistent, bioaccumulative, and toxic” (PBT) compounds that are created as byproducts of chemical manufacturing, and also from combustion. Dioxin/furans are known to affect 

hormone levels and functions, as well as affecting fetal development, the immune system, and 

reproduction. They are toxic at levels that already exist in the environment. EPA states: “Because dioxins 

are widely distributed throughout the environment in low concentrations, are persistent and 

bioaccumulated, most people have detectable levels of dioxins in their tissues. These levels, in the low 

parts per trillion, have accumulated over a lifetime and will persist for years, even if no additional

exposure were to occur. This background exposure is likely to result in an increased risk of cancer and is 

uncomfortably close to levels that can cause subtle adverse non-cancer effects in animals and humans.”