•MASSPIRG 

Massachusetts Public Interest Research Group 

44 Winter Street 

Boston, MA 02108 

(617) 292-4800 (ph) 

masspirg@pirg.org 

www.masspirg.org 

(617) 292-8057 (fx) 

June 24, 2004 

Robert Donaldson 

Department of Environmental Protection 

Bureau of Waste Prevention 

One Winter Street, 8th floor 

Boston, MA 02108 

Dear Mr. Donaldson, 

Attached please find three documents that constitute testimony and comments of the 

Massachusetts Public Interest Research Group (MASSPIRG) on the Department's 

proposed emissions regulations for engines and turbines. 

The documents are: 

• "Testimony of MASSPIRG," 

• "Health Risks of Exhaust from Diesel-Fueled Electric Generators" by Geoff Keith of 

Synapse Energy Economics, and 

• "Micropower at the Crossroads," a report by MASSPIRG. 

"Micropower at the Crossroads" contains the analysis I referred to in my oral testimony 

when I estimated that existing distributed generators in the metro Boston area could emit 

approximately 2.7 tons per day of NOx during peak use. As I mentioned this is a rough 

calculation (and I would appreciate your observations or comments on our analysis), but 

it is a useful indicator of the size of the air pollution problem that the Department is 

working to solve by implementing these regulations. 

I greatly appreciate your attention to this issue, and am available anytime to discuss our 

comments. 

Sincerely, 

frame piorke 

Energy Advocate 

617.747.4316 
MASSPIRG 

Testimony of MASSPIRG on the Emission Standards for Stationary Engines and 

Combustion Turbines at 310 CMR 7.20 

Frank Gorke, Energy Advocate 

June 24, 2004 

The Massachusetts Public Interest Research Group (MASSPIRG) appreciates this 

opportunity to comment on the Department's Proposed Amendments to 310 CMR 7.00 

and 310 CMR 70.00 issued in May 2004. MASSPIRG strongly supports the 

Department's intent and philosophy in promulgating emissions standards for engines and 

combustion turbines, and greatly appreciates the Department's work in preparing and 

promulgating this regulation. 

The adoption of updated and new emissions standards for engines and turbines used for 

onsite generation of electrical power ("Distributed Generation" or "DG") is critical given 

the increasing usage of these technologies. While DG holds the potential to increase the 

efficiency of the electrical system and provide other benefits, DG also presents an 

environmental threat due to the wide range of emission rates associated with different 

technologies and vintages of DG installations, the proximity of many small engines and 

turbines to affected populations, and the likelihood that these sources will have their 

highest utilization under peak electrical load conditions that typically coincide with poor 

air quality. Emissions standards are an essential component of the effort to ensure that 

the benefits of DG are not compromised by environmental and human health costs 

associated with the usage of older and dirtier DG technologies. 

In comments submitted to the Department in October, 2003 MASSPIRG supported 

several provisions of the proposed rule: 

• the standards proposed for non-emergency engines and turbines, 

• the standards proposed for small emergency engines, and 

• the inclusion of CO2 in the pollutants to be regulated. 

We urged the Department to address: 

• the omission of CO standards for emergency turbines, 

• the omission of mandatory reviews of the standards for emergency generators, 

and 

• the omission of provisions that credit simultaneous emission reductions.1 

Finally, we questioned why the Department proposed different standards for small and 

large emergency engines, and why the Department did not propose an ammonia standard 

for non-emergency engines. 

1

 Comments of MASSPIRG and CLF on the Draft Emission Standards for Stationary Engines and 

Combustion Turbines at 310 CMR 7.20. Submitted October 10, 2003. 
I. The RAP Model Rule provides a strong and appropriate foundation for state 

emission standards. 

We are pleased that, in several important areas, the Department's proposed amendments 

follow the model rule developed in the stakeholder workgroup led by the Regulatory 

Assistance Project (the "Model Rule"). In these areas, the proposed amendments 

maintain the positive features of the Department's earlier proposal. The Model Rule 

incorporated broad participation by air regulators, environmental groups and engine and 

turbine manufacturers; and participants in the process relied on a considerable amount of 

data, developed by independent consultants, regarding the current and expected future 

capabilities of different engine and turbine technologies. As a result, it provides a solid 

foundation for state emission standards. 

In particular, MASSPIRG supports the emission standards proposed for non-emergency 

engines and turbines (Tables 2 and 3 in proposed 310 CMR 7.26(43)), with one caveat. 

The standards proposed for non-emergency engines and turbines are both aggressive and 

reasonable, and they will not impose undue burdens on either generator manufacturers or 

customers installing DG systems. In fact, given that Massachusetts is classified as a nonattainment area for ozone, the Department should follow several other states and adopt 

more stringent NOx standards. California has established a NOx standard for small 

generators of 0.5 lbs/MWh through 2006 dropping to 0.07 lbs/MWh in 2007. Air 

regulators in Texas have established a general permit with a NOx limit of 0.14 lbs/MWh 

in 2005 for the East Texas non-attainment area (see chart below). 

While current diesel fueled engines will have trouble meeting the proposed NOx 

standards, other reciprocating engines will be able to meet them. Lean-burn engines 

fueled by natural gas can achieve the proposed 2004 NOx standard today with SCR 

controls, and with reasonable R&D efforts, these units will be able to meet the proposed 

2008 and 2012 standards. Rich-burn engines fueled by natural gas can also currently 

meet the proposed 2004 NOx standard by using a three-way catalyst, and these units too 

should be able to meet the 2008 and 2012 standards. It is worth noting that diesel-fueled 

engines will continue to be the technology of choice for emergency generation, and in the 

near to medium term, the emergency generation market is likely to remain as large or 

larger than the market for other types of onsite generation. It should also be noted that, 

given past advances in emission controls, the "technology forcing" nature of this 

regulation and the more stringent DG standards being adopted in other states, it is not 

inconceivable that diesel engines could meet these standards at some point in the future. 

The assertion that the Department's proposed standards for non-emergency generators are 

reasonable is supported by two facts. First, these standards are consistent with the 

standards developed for the Model rule, and as noted, the Model rule is the product of 

intensive stakeholder negotiations and third party research. Second, the proposed 

standards are more lenient than the DG standards adopted in several other states. The 

chart below compares the Department's proposed NOx standards for non-emergency 

engines with the standards in the Model rule, the standards adopted in California, the 

standardized DG permit adopted in East Texas and the permit under consideration in 

Connecticut. '• 

2 
MASSPIRG also finds the Department's proposed standards for small emergency engines 

and for emergency turbines to be sufficient to protect the environment and human health, 

given the operating limitations on these generators. By adopting the US EPA non-road 

standards for small emergency engines, the Department is adopting aggressive emission 

standards that also minimize the administrative burden on the Department and the 

regulatory burden on engine manufacturers. Because these are standards for which 

engine manufacturers are already planning, they allow for efficient product development 

and will impose very small (if any) additional costs on these companies. 

We also find the NOx standard for emergency turbines to be appropriate. 

As discussed in the section on Combined Heat and Power, we urge the Department to 

adopt additional provisions of the RAP Model Rule. 

II. There are compelling health reasons limiting the operation of older dieselfired distributed generation. 

A recent paper examining the scientific literature on the health effects of diesel exhaust 

found strong evidence that acute and sub-chronic exposure to moderate levels of diesel 

exhaust result in very significant non-cancer health effects and may also lead to cancer. 

(A copy of this paper is attached to this testimony.) The paper focuses on studies of 

short- and medium-term exposure since that is the type of exposure most likely to occur 

from increased use of diesel generation. Less serious effects of exposure include 

coughing, wheezing, and eye and nose irritation and exacerbation of existing allergies. In 

addition, an inflammatory and immunological response at the cellular level, in both the 

respiratory and cardiovascular systems, is consistently observed with short-term exposure 

to diesel exhaust. 

People with lung and heart disease suffer even more serious risks from exposure to diesel 

exhaust. A large body of epidemiological work documents an association between 

exposure to fine particulate matter and acute illness and mortality in people with heart 

and lung disease. Two facts suggest that diesel exhaust plays a significant role in these 

observed health effects. First, fine particulates from diesel engines makes up a 

significant portion of ambient fine particulate matter in many of the urban areas studied. 

Second, although there are associations with several pollutants, the strongest association 

is between fine particulates and daily health effects, and over 90 percent of the particulate 

matter by mass in most DE is fine particulate matter. Work is ongoing to understand the 

mechanisms underlying this association and the specific particles at cause, and much of 

this work is focused on the cellular inflammatory/immunological response. 

The existing data on the carcinogenicity of diesel exhaust is inadequate to determine 

whether acute and sub-chronic exposure leads to cancer. There is strong evidence that 

chronic exposure leads to cancer, and based on this evidence the US EPA has listed diesel 

exhaust as a probable carcinogen and the California Air Resources Board has listed it as a 

known carcinogen. However, both agencies have stated that there is no known threshold 

for the carcinogenic effects of diesel exhaust and that shorter-term exposures may lead to 

cancer. Diesel exhaust contains a number of known mutagens-and carcinogens, including 

aldehydes, benzene, 1,3-butadiene, and polycyclic aromatic hydrocarbons (PAHs), which 

provide a plausible mechanism for a non-threshold, mutagenic mode of action. 

3 
III. The DEP's rule should provide credits for CHP applications. 

As noted by the Department, the RAP Model Rule allows credits for combined heat and 

power ("CHP") where waste heat from the engine is put to productive thermal use, such 

as heating or cooling. The Department questions this provision, stating its concern that 

such a provision would allow installation of a "dirtier," non-state-of-the art, engine or 

combustion turbine, relative to what would be allowed absent the CHP credit provision of 

the RAP Model Rule. MASSPIRG understands this concern of the Department, and 

agrees that if including the CHP provision led to a net increase in emissions from the 

sources subject to the proposed regulations, it would not be appropriate to include it in 

the final rule. Further, MASSPIRG understands that administration of the RAP model 

rule provision could increase the administrative burden on the Department in ensuring 

that the provisions of the proposed regulations were being met in a monitorable, 

verifiable manner. 

However, MASSPIRG believes that the Department's concerns can be fully addressed 

with a slight modification of the RAP Model Rule's provisions, and encourages the 

Department to take this step because it is essential to provide even modest financial 

incentives for more efficient uses of energy and for the replacement of old boilers, which 

typically have very high emission rates. The importance of the financial incentive 

associated with crediting CHP applications is magnified by the fact that the most 

economic opportunities for CHP installations - large industrial sites - have generally 

made such investments already. The remaining (smaller) commercial and industrial 

opportunities for installation of CHP face at best a marginal cost, benefit calculus when it 

comes to cogeneration investments. 

Importantly, credits for cogeneration would be fully aligned with the Department's 

pollution prevention philosophy and complementary to its existing initiatives to reward 

generation efficiency, including the migration of electricity sector rate-based emission 

control programs to emission standards based on emissions per unit of electrical output 

(i.e., "output-based" standards), rather than heat input (310 CMR 7.29), and the 

administration of the state's NOx allowance trading program through an output-based 

allocation (310 CMR 7.28). It would also recognize that the benefits of cogeneration at 

the small engine level are conceptually identical to the benefits provided by large CHP 

facilities, which are granted credit for coincident steam use in the NOx allowance trading 

program. Credit for CHP applications in the proposed regulations would also be 

consistent with other state and federal efforts to emphasize pollution prevention rather 

than only pollution reduction (including, for example, EPA's output-based standard for 

its New Source Performance Standards regulation for large electric utility steam 

generators (40 CFR 60, Subpart Da), Connecticut and New Jersey regional NOx program 

allocations that use a form of output-based standards, EPA's guidance documents on 

output-based methods to assist states in designing rate-based and allowance allocation 

programs (including guidelines for specific allocation credit for CHP applications), and 

federal legislative proposals for multi-pollutant regulations using output-based 

standards). Incorporating incentives to improve efficiency in every aspect of emission 

control requirements, including economic incentives for the expansion of CHP, is 

critically important in light of the daunting C02 reductions needed to address global 

climate change. Unlike other pollutants, the only way to reduce C02 emissions.is by 

4 
switching fuels or increasing the efficiency of energy conversion. Thus, the US needs to 

enhance its use of CHP considerably and quickly. 

The focus on pollution prevention and efficiency has been incorporated in other states' 

DG emission standard rules, as other states have considered it important to include a 

steam-use credit for CHP applications. For example, the California rule, the East Texas 

DG permit, and the draft Connecticut permit all include provisions for emission 

reductions due to CHP. The draft Connecticut rule also includes provisions to credit 

reduced flaring. 

MASSPIRG strongly urges the Department to adopt a CHP provision similar to the one 

in the Model rule. The participants in that process spent considerable time developing a 

method of calculating emissions displaced by the use of byproduct heat, and we find this 

method to be sound and appropriate for this purpose. However, MASSPIRG recognizes 

the Department's concern, and agrees that provisions for credits should guard against 

gaming the credits, and establishing a mechanism that fails to achieve actual emissions 

reductions. 

The RAP Model Rule includes specific mechanisms for ensuring that emissions 

reductions are real beyond the time of certification. For example, the Rule includes 

threshold requirements for a CHP installation's eligibility for credits as well as a cap on 

historic emission rates that can be used in retrofit cases (see Section VII of the Rule). 

MASSPIRG believes that the RAP Model Rule provides an appropriate approach to 

determining credits for CHP installations. 

Nevertheless, if the Department is uncomfortable with the prospect of "free ridership," it 

should not abandon the crediting of CHP altogether - instead, it should consider other 

options for reducing this likelihood, and for making the credit provisions more verifiable 

and enforceable. First, the Department could require that, for both new facilities and 

existing facilities, the displaced emissions be calculated using emission rates of new gas 

fired boilers (rather than the dual approach proposed in the Model Rule). This approach 

would guard against giving "too much" credit in situations where, due to economics, an 

older boiler was going to be replaced anyway. Furthermore, the Department could make 

obtaining the credit dependent on three factors: (1) demonstration on an annual basis that 

the facility owner has not installed a new, separate boiler, (2) demonstration that the old 

boiler has been removed, and (3) demonstration that the facility owner continues to have 

steam demand that is met by the CHP application at a level that is roughly equivalent to 

historical use. These three requirements would go a long way to making the emission 

reductions verifiable and enforceable, and the administrative burden to the Department of 

administering such a provision could be transferred to the facility by demonstration 

requirements written into the operating permit or certificate. 

While these reduced provisions for administration of a CHP credit (relative to the RAP 

Model Rule) could address the Department's substantive concerns and administrative 

burdens, what remains unsatisfactory is that there are likely to be some situations where 

only the provision of credits can make the replacement of a boiler economic; and that in 

the absence of the credit an old boiler will not be replaced. In this case, the emissions 

reduction would be undervalued under a mechanism that only provides a credit based on 

the emission rate of a new gas-fired boiler. Before adopting such a reduced credit 

5 
mechanism, the Department should discuss with interested parties alternative 

mechanisms for addressing this situation. 

IV. The Department should provide credits for concurrent emission reductions 

achieved by reduced flaring of waste gases. 

While flaring is necessary to reduce the impacts of certain pollutants, it wastes valuable 

energy that should be put to use. Given that flaring is required in Massachusetts for 

many facilities, owners of engines and turbines at such facilities should be allowed to net 

avoided emissions from flaring against their emissions for compliance purposes. The 

Model Rule allows operators either to measure emissions from a displaced flare to 

calculate avoided emissions or to use default emission rates defined in the rule. We 

believe that this is a sound approach to calculating emissions avoided by reduced flaring. 

V. The Department should consider establishing more stringent NOx standards 

for non-emergency engines and turbines (Tables 2 and 3 in proposed 310 CMR 

7.26(43)) 

The Department should consider establishing emissions standards for NOx, more 

stringent than the RAP Model Rule, along the lines of the standard adopted in California 

and the general permit adopted in East Texas (see chart below). 

NOx Emission Standards for Distributed Generation in Non-Attainment Areas 

0.7 

2004 2005 2006 2007 2008 2009 2010 2011 2012 

VI. The Department should explain why an ammonia standard has not been 

proposed for non-emergency engines. 

Undoubtedly, some engines will comply with the proposed emission standards using 

selective catalytic reduction (SCR) systems; thus the risk of ammonia slip will be present. 

Despite our request in our October comments, the Department has not explained its 

approach on this issue. We urge the Department to address this issue and, absent a 

compelling rationale, to expand the proposed ammonia standard to apply to both turbines 

and engines. 

6 
VII. The Department should adopt a carbon monoxide (CO) standard for small 

emergency turbines (310 CMR 7.26(42) Table 1). 

Because emissions of CO can rise as combustion processes are managed to minimize 

NOx emissions, it is important to regulate both of these pollutants to prevent a NOx 

standard from resulting in unintended increases in CO emissions. We believe that a CO 

standard of 0.5 lb/MWh would limit CO emissions from small turbines appropriately 

while still allowing these units to meet the NOx standard comfortably. 

VIII. Large engines (output of over 1 MW) used as emergency generators should 

either meet a more rigorous NOx standard than smaller engines or be held to the 

same standard as small engines. 

MASSPIRG is troubled by the large emergency engine standard contained in the 

proposed rule. These standards are more lenient than the Tier 2 non-road standards 

(proposed for small emergency engines) for NOx yet more stringent for CO.2 The 

proposal of two standards is puzzling, given that (a) it would be simpler to apply the 

federal non-road standards to all emergency engines and (b) NOx is a particularly 

problematic pollutant in the Northeast. As the Department is well aware, emergency 

engines are most likely to be used on hot summer days, periods when the risk of 

exceeding the ambient ozone standard is very high. 

We firmly believe that large engines (output of over 1 MW) used as emergency 

generators should either meet a more rigorous NOx standard than smaller engines or be 

held to the same standard as small engines. Absent a compelling rationale, MASSPIRG 

urges the Department to apply the EPA non-road standards to all emergency engines. 

IX. We urge the Department to include provisions for mandatory review of the 

standards applicable to emergency generators. 

The proposed rule includes a requirement for review of the standards applicable to nonemergency generators (in 2010 and in 2017 and every five years thereafter). Broadening 

this review requirement to apply to the emergency generator standards would add little 

additional work for the Department, and it would ensure that Massachusetts citizens 

benefit from any relevant advances in technology in the coming years. Periodic review 

of emission standards is important, because Massachusetts citizens will live with new 

power plants - both large and small - for many years. 

X. MASSPIRG strongly supports the inclusion of an emission standard for C02. 

The Commonwealth of Massachusetts, through its air emissions regulatory program, has 

assumed a critical national role by regulating C02 emissions. The promulgation of 310 

CMR 7.29 set the Commonwealth on this path, and these regulations are the logical next 

step down that path. By regulating C02, the Department is effectively fulfilling the 

environmental and public health protection mandate of its enabling legislation and 

2

 The Department's proposed NOx standards are 18.3 lbs/MWh for engines between one and two MW in 

size and 16.3 lbs/MWh for units two MW and larger. The 2006 Tier 2 non-road standard for NOx and 

NMOCs combined is 14.1 lbs/MWh. The Department's proposed CO standards are 5.0 and 1.5 

respectively, and the 2006 Tier 2 CO standard is 7.7 lbs/MWh. 

7 
responding to the challenge of the Climate Action Plan of the New England Governors 

and Eastern Canadian Premiers. 

XI. Summary 

MASSPIRG supports the Department's promulgation of these emission standards. We 

also support many of the specific provisions in the Department's proposed standards. 

However, we strongly urge the Department to revisit its omission of several important 

components of the emission regulations. These omitted components are: provisions for 

the crediting of concurrent emission reductions from CHP and reduced flaring, CO 

standards for emergency turbines, and a provision for reviewing the emission standards 

for emergency generators. We urge the Department to hold large emergency engines to a 

standard at least as stringent as the standard for small ones. Finally, we question why an 

ammonia standard has not been proposed for non-emergency engines. 

8 
Health Risks of Exhaust from Diesel-Fueled Electric Generators 

Geoff Keith, Synapse Energy Economics, June 21, 2004 

22 Pearl St., Cambridge MA, 02452, www.synapse-energy.com 

Executive Summary 

This paper examines the scientific literature on the health effects of diesel exhaust 

("DE"), to shed light on the potential health risks of operating urban diesel generators 

more intensively. We focus on studies of short- and medium-term exposure ("acute" and 

"sub-chronic" exposure), that is, exposure for periods of several hours to several weeks. 

We focus on these studies because this is the type of exposure that would result from 

increased use of diesel generators and because the mechanisms triggered by chronic 

exposure, and the resulting health effects, may be different than those triggered by 

shorter-term exposures. 

There is strong evidence that acute and sub-chronic exposure to moderate levels of DE 

results in non-cancer health effects. DE also contains known mutagens and 

carcinogens, and these chemicals represent a plausible mechanism for cancer resulting 

from acute and sub-chronic exposure. However, there is considerable uncertainty 

around the potential for cancer from non-chronic exposure. DE also contributes to urban 

smog, which poses health risks to asthmatics and other subgroups. However, smog is a 

regional problem, caused by pollution from many different sources, and diesel 

generators are a relatively small source of smog precursors. Thus we do not address the 

health effects of smog here. 

In a number of laboratory tests, healthy humans have been exposed to moderate levels 

of DE, in the range of 100 to 300 ug/m3 of diesel particulate matter ("DPM"). (DPM is 

commonly used as a surrogate measure of whole DE.) Consistently observed symptoms 

include coughing, wheezing and eye and nose irritation. Dizziness, nausea and other 

neurological symptoms can result from exposure to higher concentrations. DE has also 

been shown to exacerbate existing allergies. In addition to these symptoms, exposure to 

DE results in well documented inflammatory and immunological responses at the cellular 

level in both the respiratory and cardiovascular systems. A considerable body of animal 

research provides additional information about this inflammation/immune response. 

Exposure to DE may pose much more serious risks, however, to people with lung and 

heart disease. Epidemiological studies have established a clear link between exposure 

to urban fine particulate matter and daily illness and mortality from lung and heart 

disease. Work is ongoing to understand the mechanisms underlying this association and 

the specific particles at cause, but it appears that the cellular responses to particulate 

exposure include mechanisms that can cause acute respiratory and cardiac distress and 

death. Two facts suggest that DE plays a significant role in the dynamic. First, diesel 

particulate matter makes up a significant portion of ambient fine particulate matter in 

many of the urban areas studied. Second, although there are associations with several 

pollutants, the strongest association is between fine particulates and daily health effects, 

and over 90 percent of the particulate matter by mass in most DE is fine particulate 

matter. 
The research on DE exposure and cancer has yielded less certain conclusions. There is 

reasonably strong epidemiological evidence that chronic exposure to DE (usually studied 

in an occupational setting) leads to lung cancer. Chronic exposure to high 

concentrations has also been shown to produce lung tumors in rats. Based largely on 

the epidemiological data, the US EPA has labeled DE a "probable" carcinogen, and the 

California Air Resources Board has labeled it a "known" carcinogen and established a 

unit risk number for chronic exposure. However, these findings may tell us little about 

whether shorter-term and more periodic exposure to DE can cause cancer. 

The strongest evidence that short-term exposure could lead to cancer lies in the known 

carcinogens and mutagens within DE. These chemicals include benzene, formaldehyde, 

acetaldehyde, acrolein and PAHs. Importantly, there is no known threshold for the 

carcinogenicity of some of these chemicals (e.g., benzene). However, more work needs 

to be done to determine whether these chemicals produce cancer in the case of 

inhalation exposure to DE. Currently, the weight of evidence suggests that longer 

exposure periods are more likely to lead to cancer than shorter ones, but that the 

potential for cancer resulting from shorter-term exposure, via a non-threshold, mutagenic 

mode of action, cannot be ruled out. 

The risk of acute illness and mortality to people with heart and lung disease appears to 

be the most serious health risk posed by an urban diesel generator. The current shortterm ambient air quality standard for PM2 5 is 65 ug/m3

. Based on data from the US EPA 

and other sources regarding ambient concentrations of DPM at urban locations and in 

occupational settings, it is reasonable to assume that a diesel generator in an urban 

setting, operating for a period of several hours, could create localized concentrations of 

PM2 5 above 65 ug/m3. 

2 
I. Introduction 

Most urban areas in the US are home to many, small diesel-fueled electric generators. 

Unlike large power plants, these units are often located in densely populated areas, and 

they do not have tall smokestacks to disperse their air emissions. Historically, these 

generators have been operated at very low utilization rates, with most of them operated 

as "emergency generators," that is, operated only during power outages. However, with 

the deregulation of the electric industry in some regions of the country, there has been 

pressure to allow facilities with diesel generators to operate the units during periods of 

high prices. Utilized in this way, diesel generators might operate for entire afternoons on 

many summer days, when .electricity demand and prices are high. 

This paper examines the scientific literature on the health effects of diesel exhaust 

("DE"), to shed light on the potential health risks of operating urban diesel generators 

more intensively. We focus on studies of short- and medium-term exposure ("acute" and 

"sub-chronic" exposure), that is, exposure for periods of several hours to several weeks. 

We focus on these studies because this is the type of exposure that would result from 

increased use of diesel generators and because the mechanisms triggered by chronic 

exposure, and the resulting health effects, may be different than those triggered by 

shorter-term exposures. 

Sections II and III below provide brief background on diesel electric generators and their 

emissions Section IV examines the non-cancer health effects of exposure to DE, and 

Section V examines the research on cancer and exposure to DE. 

II. Diesel-fueled electric generators 

There are a large number of diesel-fueled generators in most urban areas of the US. 

Unlike large power plants, the exact number and location of diesel generators is not well 

known. Only recently has there been interest in developing detailed inventories of these 

units. In 2003, the Northeast States for Coordinated Air Use Management (NESCAUM) 

released an initial assessment of the population of diesel-fueled generators in the 

Northeast.1 This assessment is based on data from Power Systems Research (PSR) 

and reviews of state permit data. PSR estimates the number of engine generators in the 

Northeast using a database on US engine sales, imports and exports and telephone 

surveys of engine owners. NESCAUM staff compared the estimate generated by PSR to 

permit information available from state environmental agencies. (The assessment 

covered Connecticut, Maine, Massachusetts, New Hampshire, New York, Pennsylvania, 

Rhode Island and Vermont.) 

As seen in Table 1, the number of generators estimated by PSR exceeded the number 

indicated in permit records considerably. NESCAUM notes that this is probably due to 

several factors: the permit information reviewed for many states was incomplete, many 

engines fall below the size thresholds of permitting requirements, some engines that 

should have permits do not have them, and there is likely to be some range of error in 

the PSR estimates. 

Note that the PSR estimates are far in excess of the permit records in the smaller size 

ranges, while the two sources are more consistent for the larger sized engines. This is 

because operating permits are not typically required for the smallest engines, while 

permits are required and reporting requirements are strict for the largest ones. Thus, the 

two sources leave much more uncertainty around the number of small generators in the 

Northeast. 
Table 1. Data from the NESCAUM Assessment of Stationary Diesel Engines 

Size (kW) PSR Estimates Permit Records 

25-50 1,768 156 

50-100 7,280 523 

100-250 11,557 2,729 

250-500 7,156 2,436 

500-750 1,659 1,772 

750-1000 1,507 1,335 

1000-1500 1,357 1,290 

1500+ 1,394 1,145 

Total 33,678 11,386 

The NESCAUM assessment indicates that roughly 75 percent of the diesel generating 

capacity in the Northeast is designated for emergency use. As noted, emergency 

generators are limited to several hundred hours of operation per year. However, this 

leaves roughly 25-percent of the capacity that is not permitted as emergency capacity 

and thus may be operating a considerable amount during periods of peak electricity 

demand. 

The emission rate of a diesel generator is primarily a function of two factors: the type of 

unit (emergency, peaking or baseload) and the age of the unit. Generally, emergency 

units have the highest emission rates and baseload units have the lowest. This is 

because air regulators have historically thought in terms of total annual emissions. Units 

subject to strict operating limitations can have substantially higher emission rates and 

still have total annual emissions similar to units that operate more. Regarding age, older 

generators of all types tend to have higher emission rates than newer ones, because 

regulators require lower emission rates for new units over time, as technology evolves. 

Thus, the lowest-emitting diesel generators are likely to be newer units permitted for 

non-emergency use, and the highest emitting ones are likely to be old emergency 

generators. Typical emission rates for emergency generators are shown in Table 3 

below. 

III. Diesel exhaust 

Diesel exhaust is a mix of gases, vapors and small particles. The specific ratio of gases 

and vapors to particles depends on the type of engine, the fuel and lubricants used and 

on operating conditions. The gas/vapor portion of DE consists primarily of typical 

combustion products: water vapor, oxygen, carbon dioxide (C02 ), and nitrogen oxides 

(NOx), but it also includes smaller quantities of many toxic substances. EPA has listed 

over 40 substances found in DE as hazardous air pollutants, and the International 

Agency for Research on Cancer (IARC) has listed 15 of them as carcinogens or 

probable carcinogens. The particulate matter in DE consists primarily of unburned 

carbon, and the vast majority of it falls into the category of fine particulate matter. 

Gases and vapors 

The toxic gases prevalent in DE include: carbon monoxide (CO), sulfur oxides (SOx) and 

volatile organic compounds such as alkenes, aldehydes, aromatic hydrocarbons and 

polycyclic aromatic hydrocarbons (PAHs). 

Low molecular weight compounds make up a majority of the gas-phase organic 

compounds in diesel exhaust, with acetaldehyde, formaldehyde and acetone accounting 

for more than half. Alkanes make up a smaller fraction of these compounds. The 

4 
majority of the higher molecular weight compounds consists of branched and cyclic 

hydrocarbons. 

From a toxicological perspective, the most dangerous organic compounds in diesel 

exhaust are the aldehydes, benzene, 1,3-butadiene, and polycyclic aromatic 

hydrocarbons (PAHs). Table 2 lists the most important air pollutants and toxic chemicals 

in DE and summarizes their health effects. 

Table 2. Important Constituents of DE and Their Known Health Effects 

DE Component Atmospheric 

Reaction Products 

Biological Impact 

Carbon dioxide Major contributor to global warming 

Carbon monoxide Highly toxic to humans 

Oxides of nitrogen Nitric acid, ozone Nitrogen dioxide is a respiratory tract irritant and major 

ozone precursor. Nitric acid contributes to acid rain. 

Sulfur dioxide Sulfuric acid Respiratory tract irritation; contributor to acid rain 

Alkanes (#C18) Aldehydes, alkyl 

nitrates, 

Respiratory tract irritation. Reaction products are ozone 

precursors (in the presence of NOx). 

Alkenes (#C4) 

(e.g., 1,3-butadiene) 

Aldehydes, ketones Respiratory tract irritation. Some alkenes are mutagenic 

and carcinogenic. Reaction products are ozone 

precursors (in the presence of NOx). 

Formaldehyde Carbon monoxide, 

hydroperoxyl radicals 

Formaldehyde is a probable human 

carcinogen and an ozone precursor 

(in the presence of NOx). 

Higher aldehydes (e.g., 

acetaldehyde, acrolein) 

Peroxyacyl nitrates Respiratory tract and eye irritation; causes plant 

damage. 

Monocyclic aromatic 

compounds (e.g., 

benzene, toluene) 

Hydroxylated and 

hydroxylated-nitro 

derivativesa 

Benzene is toxic and carcinogenic in humans. Some 

reaction products are mutagenic in bacteria. 

PAHs (<4 rings) (e.g., Nitro-PAHs (4 rings) Some of these PAHs and nitre- PAHs are known 

phenanthrene, 

fluoranthene) 

mutagens and carcinogens. 

Nitro-PAHs (2 and 3 

rings) (e.g., 

nitronaphthalenes) 

Quinones and 

hydroxylatednitro 

derivatives 

Some reaction products are mutagenic in bacteria. 

Elemental carbon none Nuclei adsorb organic compounds; size permits transport 

deep into the lungs (alveoli) 

Inorganic sulfate and 

nitrate 

none Respiratory tract irritation 

Hydrocarbons (C14-

C35) 

Little information; 

possibly aldehydes, 

ketones, and alkyl 

nitrates 

Unknown 

PAHs (>4 rings) (e.g., 

pyrene, 

benzofalpyrene) 

Nitro-PAHs ($4 

rings)a 

Nitro-PAH lactones 

Larger PAHs are major contributors of carcinogens in 

combustion emissions. Many nitro-PAHs are potent 

mutagens and carcinogens. 

Nitro-PAHs ($3 rings) 

(e.g., nitropyrenes) 

Hydroxylated-nitro 

derivatives 

Many nitro-PAHs are potent mutagens and carcinogens. 

Some reaction products are mutagenic in bacteria. 

Source: USEPA, Health Assessment Document for Diesel Engine Exhaust (p. 2-87,91). 

Particulate Matter 

Air regulators divide particulate air pollution into several categories based on its size, as 

measured in microns. (A micron is about one seventh the width of a human hair.) The 

largest particles fall into the category of PM1 0 , particles with a diameter of ten microns or 

less. Fine particulates, or PM2 . 5 , are the subset of PM1 0 having a diameter of 2.5 microns 

or less. The recently coined term "ultrafine particulates" refers to the subset of PM2.5 

having a diameter of one micron or less. In general, smaller particles pose greater health 

5 
threats, because they remain suspended in the air longer than larger particles and are 

more likely to travel past filtering systems in human airways into the lung. Diesel 

particulate matter (DPM) usually ranges from 10 to 35 percent of total PM2 5 in US cities. 

Typically over 90 percent of the PM emitted by diesel engines falls into the PM2 5 

category. Diesel fine particles are of particular concern from a human health perspective, 

because, as the particles are formed in the combustion process, they become coated 

with the gas- and vapor-phase toxins discussed above. The toxins typically range from 

20 to 40 percent of the total particle weight. 

Diesel engines emit particulates at rates significantly greater (as much as 20 times 

greater) than gasoline engines. This is primarily because diesel fuel is less volatile than 

gasoline, and it is still largely in liquid form when injected into the cylinder for 

combustion. Gasoline, in contrast, is injected primarily in gaseous form. The liquid/gas 

mixture of diesel fuel burns less completely than gasoline. Hydrogen is stripped from the 

diesel hydrocarbons, and the remaining carbon tends to aggregate into particles. A 

number of factors determine the amount of particulate emission from a given diesel 

engine, including the condition of the fuel injectors, the design of the combustion 

chamber, the seal of the piston rings and the presence of lubricating oils at combustion. 

The US has had ambient air quality standards for PM1 0 since the 1970s. States strive to 

achieve these air quality standards by, among other things, requiring engine operators to 

obtain operating permits, which include emission rate limits. (Ambient air standards for 

PM2 5 were promulgated much more recently so operating permits have only recently 

begun limiting PM2 5 .) As engine technology has advanced over time, the emission limits 

facing new engines have become more stringent, however these more stringent 

requirements have been applied only to new engines. Most existing engines have been 

"grandfathered" under their original permit limits. Because many electric gensets are 

operated a small number of hours per year, these engines tend to remain in operation 

for longer periods than truck engines. This has left the US with an existing fleet of 

relatively old, high-emitting electric gensets. 

Table 3 shows emission rates typical of today's emergency generators in the US These 

emission rates, from the US EPA, represent those of an emergency generator in the 

range of 10 to 30 years old. The emission rates are shown in terms of pounds emitted 

per Megawatt-hour of electricity produced. Note that the vast majority of the particulate 

matter emitted is PM2 5 . 

Table 3. Typical Emission Rates for an Emergency Generator 

Pollutant Emission Rate (Ib/MWh) 

NOx 30 

so2 

3 

C 02 1610 

PM1 0 0.57 

P M 2 5 0.50 

Formaldehyde 0.0008 

Acetaldehyde 0.0003 

Acrolein 0.0001 

Benzene 0.0078 

PAH 0.0021 

NOx emissions contribute to urban smog; S02 is the primary cause of acid rain; and C02 

is the primary cause of climate change. Particulate matter and the toxic pollutants are 

the source of the major local health effects discussed below. 

6 
Exposure to diesel generator exhaust 

If diesel generators began operating during periods of high electricity prices, in addition 

to during power outages, this would probably result in operation for four to six hour 

periods on very hot summer afternoons. This type of operation would result in short-term 

exposure to DE for people who lived or worked near the generator. It would probably not 

result in chronic exposure for these people. 

There have been few detailed studies of the concentrations of DE likely to result from the 

operation of urban diesel generators, and more work needs to be done in this area. In 

particular, work is needed to characterize better the concentrations that can result when 

tall buildings slow the dispersion of pollutants from urban sources. However, estimates 

and measurements have been made of DE concentrations in different places and over 

various time periods, and a these data provide a basis for estimating DE concentrations 

near urban diesel generators. 

Modeling studies performed during the 1980s estimated annual average DPM 

concentrations of 2 to 13 micrograms per cubic meter (pg/m3) in urban and suburban 

areas, with daily maximum values of 22 pg/m3.

2

 These studies took measurements of 

total PM1 0 in urban and suburban areas and used models to attribute that PM1 0 to 

different sources. DPM was estimated to constitute 7 to 36 percent of total ambient PM1 0 

on average. In studies performed during the 1990s, annual average DPM concentrations 

were lower - in the range of 1.2 to 4.5 pg/m3. The decline from the 1980s probably 

reflects declining concentrations, but may also reflect changes in modeling tools and 

methods. In specific locations DPM concentrations can reach much higher levels, 

particularly in partially enclosed spaces and where tall buildings slow dispersion. For 

example, DPM concentrations of 46.7 pg/m3 were reported at a New York City bus stop. 

Table 4 summarizes these data and concentrations from several occupational settings 

cited by EPA. Regarding the occupational data, EPA notes, that concentrations at sites 

with stationary engines are usually higher than at sites with mobile engines. Table 4 also 

shows the current ambient air quality standard for PM1 0 and PM2 5 . However, note that 

DPM is only one portion of total PM, so the DPM concentrations in this table are not 

directly comparable to the PM standards. (As these numbers imply, the PM standards 

are commonly exceeded in large cities and can be exceeded by quite a bit in 

occupational settings.) 

Table 4. Comparison of DPM Concentrations 

Location Type DPM concentration (pg/m"5) 

Urban and suburban annual average 1.2 to 4.5 

Urban and suburban daily maximum 22 

NYC bus stop daily maximum 47 

Occupation 

Mining daily maximum 7-1,280 

Railroad daily maximum 39-191 

Firefighting daily maximum 4-748 

Public Transit daily maximum 7-98 

Mechanics and Dockworkers daily maximum 5-65 

Air quality standards PM concentration (ug/nT3

) 

PM1 0 annual average 150 

PM1 0 daily average ?? 

P M2 5 annual average 15 

P M 2 5 daily average 65 

Source: US EPA, Health Assessment Document for Diesel Engine Exhaust (p. 2-124,125). 

7 
Based on the available data on DPM concentrations in various areas, it is reasonable to 

assume that a diesel generator in an urban setting, operating for a period of several 

hours, could create localized concentrations of PM2.5 well above the daily average 

standard (65 pg/m3). 

IV. Non-Cancer Health Effects 

Scientists assess the health effects of air pollutants using three types of studies: animal, 

human and epidemiological studies. All three study types have been used to assess the 

non-cancer effects of exposure to DE. In animal studies, researchers have exposed 

various species to elevated concentrations of DE under controlled conditions and 

measured the response. They have also performed a range of other experiments in vitro 

- in human and animal cell cultures. In human chamber studies, volunteers have been 

exposed to moderate levels of DE and undergone various tests before, during and after 

exposure. Descriptions of non-scientific exposure incidents also shed light on the human 

health effects. 

There are several types of epidemiological studies. In "time-series" studies, researchers 

make statistical comparisons of data on daily pollution levels and rates of illness and 

death in a given area. In "cohort" studies, researchers look for patterns of disease in 

selected groups, such as people in different locations or occupations. In "prospective" 

cohort studies, researchers follow a group or groups over time and examine patterns of 

disease. 

Reviews of the literature on the non-cancer health effects of DE have been published by 

the US EPA,3 the Health Effects Institute4 and the California Environmental Protection 

Agency.5 These reviews are more exhaustive and more technical than this one. Also, 

note that the focus here is on the effects of acute and sub-chronic exposure, because 

this type of exposure better approximates exposure to diesel-fueled electric generators. 

There is strong evidence for health effects from long-term exposure to DE, which is not 

discussed here. 

There are a range of health effects from short-term exposure to DE. These effects 

include transient symptoms such as eye irritation, coughing, wheezing, dizziness and 

nausea. At the cellular level, transient effects include inflammation and immunological 

responses. There is also substantial epidemiological evidence for more serious shortterm health effects, including hospitalization and death, in sensitive populations exposed 

to fine particulates. 

The non-cancer animal data 

Animal studies generally examine the effects of DE on lung function, respiratory tissues, 

and/or inflammation and immunological responses at the cellular level. At a large scale, 

the response of laboratory animals' airways to particulates is fairly well understood, and 

human airways are assumed to operate in generally similar ways. Readily soluble 

particles are often dissolved and cleared in mucus and other fluids. Less soluble 

particles - like DPM - are targeted by cells of the immune system, called macrophages. 

Airway epithelial cells and activated macrophages release mediators (cytokines, growth 

factors and proteases) that cause inflammation and can cause cell injury and cell 

proliferation.6 

In general, adverse effects on lung function from acute exposure are only seen in the 

context of extremely high concentrations - above several mg/m3. Lung function is 

8 
typically measured by airway resistance, expiratory volume and other indices. However, 

there is substantial evidence that acute exposure to concentrations less than this result 

in inflammation and immunological responses at the cellular level. 

Pepelko exposed young rats to 6 to 7 mg/m3 DPM for eight days and measured arterial 

blood gases, blood pH, body weight changes, lung volumes and several other indices. 

The only significant differences were in weight gain and blood pH - both lower in the 

exposed group than the control group.7 Weister et. al. exposed young guinea pigs to 6.3 

mg/m3 for 28 days and tested the animals during exposure. Increased pulmonary flow 

resistance was observed (35 percent), but there was no change in several other 

measures of lung function.8 Pepelko et. al. exposed cats to 6.4 mg/m3 DPM for 28 days, 

and observed only modest changes in lung function (decreased expiratory flow rate at 

10-percent vital capacity). On histological examination, the lung tissue appeared 

charcoal grey with black spots, and macrophage aggregates were found in the alveoli.9 

These findings demonstrate remarkably robust lung function in the face of concentrated 

particulate exposure. 

In contrast to studies of lung function, studies of the cellular response to DE have 

consistently found evidence of an immunological response. White and Garg exposed 

rats to 6 mg/m3 DPM, for time periods ranging from six hours to 63 days and examined 

immunological markers.10 After six hours, there was evidence of macrophage activity, 

and after 24 hours there was upregulation of certain immune cells. After several weeks 

there were changes in the size, content and shape of macrophages, thickening of the 

septal wall adjacent to these cells and the appearance of other inflammatory cells. 

Boutillier et. al. found an inflammation response but no change in standard lung function 

in rats exposed to 40 mg/m3 of urban particulates for four hours.11 Several studies of 

guinea pigs exposed for short periods found increased airway resistance typical of 

allergic stimulation.12,13 

The US EPA concludes from the available literature that, with acute and sub-chronic 

exposures, health effects related to lung function, when found, are mild and result from 

high DPM concentrations. The agency also concludes that there is ample evidence of 

other pathophysiologial effects from short-term exposure to lower levels of DE. These 

effects include: accumulation of DPM in pulmonary tissues, an inflammatory response, 

macrophage aggregation and accumulation, immune cell proliferation and thickening of 

alveolar walls adjacent to macrophage aggregates.14 While uncertainties remain around 

these dynamics, particularly with respect to the dose-response relationship, the effects 

are generally consistent with those observed in the human exposure data and the 

associations found by epidemiological researchers. 

The human exposure data 

Experiments in which humans are exposed to DE use moderate concentrations of DE 

(compared to the animal studies), in the range of 100 to 300 ug/m3. The most common 

and consistent effects of exposure to DE are eye irritation, coughing and complaint of an 

unpleasant smell. These symptoms are reported consistently in studies exposing 

volunteers to concentrations of 200 pg/m3 and greater. Subjects have also reported 

dizziness, lightheadedness and nausea with exposure to higher concentrations. Several 

studies examining health effects over the course of a Workshift in diesel-related 

occupations have reported all of these symptoms. Gamble et. al. performed a casecontrol study examining workers during a shift in a diesel bus garage with DPM levels in 

the range of 250 pg/m3. Exposed workers reported increased incidence of burning eyes, 

9 
headaches, labored breathing, nausea and wheeze compared to the control group (with 

a similar workshift but no DE exposure).15 

Descriptions of several incidents support these findings, but exposure was not measured 

in these cases. Several reports of miners exposed to high concentrations of DE describe 

complaints of nose and eye irritation, headaches, lightheadedness and nausea.16 

Notably, Wade et. al. describe railroad workers who developed persistent neurological 

symptoms, and asthma-like respiratory symptoms, working for long periods near diesel 

locomotives.17 

An inflammation response at the cellular level is also a common finding in human 

exposure studies, and as in the animal studies, this response is often found in subjects 

in which the standard indices of lung function are unchanged. Several studies by Rudell 

et. al. consistently found cellular markers of inflammation in fluids taken from volunteers' 

airways after controlled exposure to diluted DE. 18,1 9 Nordenhall et. al. exposed 15 

subjects to diluted DE (DPM = 300 pg/m3), and found significantly elevated markers of 

inflammation (neutrophiles and soluble proteins).20 Salvi et. al. exposed human 

volunteers to the same concentration of DPM for one hour with intermittent exercise. 

Subjects exhibited "a well-defined and marked systemic and pulmonary inflammation 

response... which is underestimated by standard lung function measurements."21 The 

observed response was characterized by increases in neutrophils and lymphocytes as 

well as histamine and fibronectin in bronchial fluids. 

The Health Effects Institute (HEI) recently published two human chamber studies, in 

which both healthy and asthmatic subjects were exposed to DE at concentrations 

varying from 23 to 311 pg/m3 of DPM. In one of these studies (Gong et. al.) there was 

very little difference in the responses of the healthy and asthmatic subjects,22 and in the 

other (Holgate et. al.), the healthy subjects showed a greater inflammation response 

than the asthmatic subjects.23 However, in both HEI studies, the healthy subjects 

presented clear inflammation responses. The researchers in the latter study state that 

"modest concentrations of diesel exhaust [100 pg/m3] have clear-cut inflammatory 

effects on the airways of nonasthmatic subjects."24 The consistent finding of a marked 

inflammation response at the cellular level with little measurable change in lung function 

suggests that this inflammation response was probably also present in studies where 

only the standard indices of lung function were measured. 

Recent research has also shown that the inflammation response to DE involves the 

cardiovascular system as well as the respiratory system. The Holgate study cited in the 

previous paragraph also found that exposure to DE resulted in parasympathetic 

stimulation of heart rate variability in both the healthy and asthmatic subjects. Another 

recent HEI study examined healthy subjects exposed to concentrated ambient 

particulates from Los Angeles. The subjects exposed to particulates showed mean 

increases fibrinogen, in a blood inflammation parameter, while the control group did 

not.25 The cardiovascular effects of DPM are discussed further in the section on noncancer epidemiological research below. 

The evidence for an allergic response to DE exposure is also persuasive. Diaz-Sanchez 

et. al. have published a number of studies on this topic, consistently documenting 

increased levels of certain mediators involved in allergic responses (e.g., IgE and 

cytokine) with exposure to DE. 2 6 In one study, subjects produced antigen-specific 

proteins at a rate 16-times greater in the presence of both DE and an allergen than in 

the presence of the allergen alone. 27,2 8 

10 
Several studies of children living or attending school near major roadways support the 

evidence for many of the health effects described above. One study found the incidence 

of cough, wheeze, runny-nose and doctor diagnosed asthma to be higher among 

children living within 100 meters of heavily traveled roads than among other children.29 

The association with asthma is interesting, given the negative findings in the HEI studies 

cited above. Brunkreef et. al. performed two studies comparing respiratory symptoms to 

proximity to traffic. 30,3 1 The two studies together found associations between proximity to 

truck traffic and a range of effects (lung function decrements, chough and wheeze, 

bronchitic and allergic symptoms), although some symptoms were found in only one of 

these studies. 

The US EPA provides an exhaustive review of the animal and human exposure data in 

its 2002 Health Assessment Document for Diesel Engine Exhaust. Based on this review, 

the agency concludes that DE probably contributes to airway inflammation and disease 

through the release of proinflammatory mediators and its tendency to exacerbate the 

effects of other airborne irritants.32 Regarding changes in lung function, EPA concludes 

that "reversible changes in pulmonary function" can occur in humans in relation to DE 

exposure, though it is not possible at this time to relate these changes to specific 

exposure levels. 

The non-cancer epidemiological data 

Over the past 15 years, epidemiologists have uncovered an association between 

ambient levels of particulate matter and daily morbidity (illness) and mortality, particularly 

in people with lung and heart disease. Work is ongoing to understand the mechanisms 

underlying this association and the specific particulates at cause, but two facts suggest 

that DE plays a significant role in the dynamic. First, diesel particulate matter makes up 

a significant portion of total particulate matter in many of the urban areas studied. 

Second, the strongest association is between DE and fine particulates, and over 90 

percent of the particulate matter by mass in most DE is fine particulate matter. 

Some of the most often cited epidemiological work on fine particulates is known as the 

"Six Cities" work. The first Six Cities study, published in 1993, was a prospective cohort 

study following 8,111 adults in the Eastern US for 15 to 17 years. After controlling for 

potential confounding factors, the study reported a significant association between longterm mortality rates and three different measures of particulate matter (PM1 0 , PM2.5, and 

sulfates). This study, and another finding a similar link between cancer and long-term 

exposure to particulates, was heavily cited in the proceedings that resulted in new 

ambient fine particulate standards in 1997, and intense debate over the work resulted in 

reconstruction and reanalysis of both studies by other researchers. Both reanalyses 

replicated and confirmed the findings of the original studies.33 

Later, a time-series study was published which focused on daily mortality in the same six 

cities.34 After controlling for time trends and weather, the study found that a 10 pg/m3 

(microgram per cubic meter) increase in the 2-day mean concentration of PM2 5 was 

associated with a 3.3-percent increase in daily mortality due to lung disease and a 2.1-

percent increase in mortality from heart disease. Moreover, the study found that fine 

particles were more closely associated with mortality than course particulates, a fact 

which implicates combustion-based pollution more than suspended dust and soil-based 

particles. This study too was reconstructed and reanalyzed by other researchers, who 

confirmed the findings of the original study.35 

11 
Other time-series studies have shown a link between fine particulates and daily mortality 

in a number of different urban areas, including London,36 Ohio,37 Philadelphia, Santa 

C|ara,39 Los Angeles, 40,41,4 2 Utah4 3 and Alabama.44 Studies have demonstrated an 

association between particulates and acute illness (as measured by hospitalization, 

hospital visits or other medical intervention) in several cities in New York 4 5 and in 

Ontario46 and Utah. 4 7 More recently, Zariobetti et. al. found an association between 

particulate levels and hospital admissions for heart and lung disease in ten US cities.48 

Peters et. al. document an association between heart attacks and PM2 5 in the greater 

Boston area4 9 and an association between interventions from implanted cardiac 

defibrillators and several pollutants (N02 , CO, and PM2 5 ) in eastern Massachusetts. 

Most of these studies control for season, temperature and humidity and other pollutants. 

Notably, several time-series studies have found associations between daily mortality and 

S02 , but not PM1 0 or TSP ("total suspended particulates"). Moolgavkar50 reports such 

findings in several areas of the US, and Lee et. al. 5 1 report such findings in data from 

seven Korean cities. These findings are consistent with the stronger link to fine particles 

than coarse particles, as S02 gas is a precursor of sulfate particles, one of the most 

prevalent fine particles. Lee concludes that "there may be collinearity problems where 

TSP and S02 are included in the same model or... TSP may function less than S02 as a 

surrogate for fine particles in the ambient air of Korea." 

Several meta-analyses have been performed, which review the epidemiological data on 

fine particulates, and these studies support the associations with daily mortality and 

morbidity.52,53 In addition, the US EPA concluded that a clear association exists in its 

1996 review of the PM air quality standards,54 and the California Office of Environmental 

Health Hazard Assessment (OEHHA) came to the same conclusion in its 1998 Risk 

Assessment for Diesel Exhaust.55 Other work has specifically investigated potential 

confounding factors in the epidemiological literature (e.g., weather and gaseous 

pollutants) and found it unlikely that the association is attributable to confounding. 56,5 7 

In 2000, the Health Effects Institute (HEI) released the National Mortality, Morbidity and 

Air Pollution Study, a two-part study designed specifically to resolve some of the 

uncertainties in the epidemiological literature.58 The first part addressed methodological 

issues in the studies, and the second part is a large-scale study of data in 90 US cities. 

In the latter paper, Samet et. al. used the same statistical techniques to examine data in 

all cities, providing both analytical consistency and a level of statistical power not found 

in previous studies. The results are "generally consistent with an average approximate 

0.5-percent increase in overall mortality for every 10 pg/m3 PM1 0 measured the day 

before death." The effect was slightly greater for deaths due to heart and lung disease 

than for total deaths. A subset of these data were published in the New England Journal 

of Medicine.59 

Recent work has focused on understanding the health effects of different types of urban 

PM. Laden et. al. compared mortality data to ambient levels of three different kinds of 

fine particles.60 The authors identified different particle types deriving from soil and 

crustal material, motor vehicle exhaust and coal combustion. Elevated levels of the 

vehicle- and coal-based particles were found to be associated with increased 

cardiovascular and pulmonary mortality, but a similar association was not found for the 

soil-based particles. The association was strongest for the motor vehicle particles. 

Recent research has also focused on gaining a better understanding of fine particulates' 

effects on people with heart disease, an association more puzzling than the one 

between particulates and lung disease. Pope et. al. found changes in heart rate 

12 
variability during periods of high particulate pollution, and Brook et. al. found brachial 

artery constriction in human volunteers simultaneously exposed to PM2 5 and ozone. 

Dockery summarizes the epidemiologic literature on particulate exposure and 

cardiovascular effects.62 

Research on the mechanisms behind the mortality/morbidity response is focusing on the 

cellular inflammation response. Much of the animal data implicates this mechanism, and 

the mechanism is consistent with the observed association between both lung and heart 

disease. As discussed above, Salvi et. al. examined inflammatory responses in the 

airways and blood vessels of human volunteers exposed to PM1 0 , and found a marked 

systemic inflammation response.63 Nemmar et. al. have performed several studies 

examining the effect of particulate exposure on thrombus development in blood vessels. 

(A thrombus is a blood clot that forms in an injured blood vessel, and vessels blocked by 

such clots are the most common cause of heart attacks.) In one study, Nemmar et. al. 

found that particles deposited in the trachea of hamsters enhanced thrombus 

development by facilitating blood platelet activation.64 A second study confirmed these 

findings, demonstrating both a pulmonary inflammation response and blood platelet 

activation.65 

Summary of non-cancer effects 

The animal and human experimental data on the non-cancer health effects of DE is, in 

the words of the US EPA, "extensive and compelling."66 Health effects of acute and subchronic exposure include transient respiratory symptoms as well as immunological and 

inflammation responses. The epidemiological evidence for fine particulate matter's role 

in mortality and morbidity is substantial. Ongoing laboratory research is focused on 

biologic mechanisms that plausibly explain this association, including the inflammation 

response identified in the animal and human studies. Based on the available data, it is 

reasonable to assume that DPM is at least at harmful to humans as ambient urban 

PM2.5. 

The US EPA has made quantitative assessments of safe levels of both PM2.5 and DPM, 

although these assessments are quite different. In 2002 EPA established a chronic, noncancer reference concentration (RfC) for diesel exhaust of 5 ug/m3

 DPM. A chronic RfC 

is defined as "an estimate (with uncertainty spanning perhaps an order of magnitude) of 

a continuous inhalation exposure to the human population (including sensitive 

subgroups) that is likely to be without an appreciable risk of deleterious non-cancer 

effects during a lifetime." In other words, EPA concludes that breathing up to 5 pg/m3 of 

DPM all the time for an entire life will not result in adverse non-cancer health effects. 

In addition to the diesel exhaust RfC, EPA established an ambient air quality standard 

for PM2 5 in 1997. This standard is an annual average of 15 pg/m3 and a 24-hour average 

of 65 pg/m3. This standard is based on the health effects - both cancer and non-cancer 

- identified in EPA's review of the scientific literature, documented in the 1996 PM 

Criteria Document 6 7 and the 1996 PM Staff Paper 6 8 In contrast to the DE RfC, the 

ambient PM2 5 standard is designed to protect the public from both acute and chronic 

exposure risks. (The RfC is not applicable to short-term exposures.) Thus, the standard 

relevant to short-term exposures is 15 pg/m3. However, considering the definition of the 

RfC ("with uncertainty spanning perhaps an order of magnitude"), the levels of the RfC 

and the PM2 5 standard are very similar. As discussed in Section III, it is reasonable to 

assume that an urban diesel generator could create PM2.5 concentrations in excess of 

the 24-hour average PM2 5 standard. 

13 
V. Cancer risk 

Taken together, the toxicological, animal and epidemiological research provides strong 

evidence that DE is carcinogenic. (Human chamber studies are not used to evaluate 

cancer endpoints.) The toxicological work focuses on the exposure of tissue and cells to 

DE extracts. The animal research includes chronic and acute exposure studies of 

laboratory animals, and the epidemiological data focuses on occupational settings where 

chronic exposure to DE is common. 

The mutagenicity of DE constituents 

DE contains both known carcinogens and known mutagens. The term "mutagen" refers 

to the ability of a chemical to induce genetic alterations (gene mutations, deletions etc.). 

All cancers involve genetic alterations, but not all genetic alterations result in cancer. 

In 1978 Huisingh et. al. first found extracts of DE to be mutagenic in salmonella 

bacteria.69 This finding triggered a considerable amount of research, primarily bioassays 

in which bacteria and mammalian cells were exposed to concentrated diesel extracts in 

vitro. This work has found DE extracts to be mutagenic in both salmonella and E. coli 

bacteria and in several mammalian cell lines. Claxton et. al. reviewed the literature on 

DE mutagenicity in 1983;70 the IARC reviewed it in 1989;71 and the US EPA reviewed it 

in 2002. 7 2 Notably, at least three studies suggest that the nitro-PAHs in DE (nitrated 

polynuclear aromatic compounds) are responsible for most of its mutagenic effects. 73,74,7 5 

The 1989 IARC paper focuses on the nitro-PAHs. 

In addition to gene mutations, extracts of DE have also been shown to cause structural 

chromosome aberrations and increases in DNA adducts in animals. Bond et. al. 

compared lung DNA adduct formation rats, mice, hamsters and monkeys. After 12 

weeks of exposure to high concentrations of diesel particulate matter, mice and 

hamsters showed no increase in DNA adducts in peripheral lung tissues, while adducts 

were increased in rats and monkeys by 60 to 80 percent.76 Shirname-More reviewed the 

animal research on DNA adducts in 1995.77 

There is also epidemiological evidence that DE causes DNA adducts in humans. Both 

Nielson et. al. and Hemminki et. al. found elevated DNA adducts in garage workers 

exposed to DE, 78,7 9 and Hou et. al. found elevated adducts in exposed bus mechanics.80 

The US EPA concludes that, "compared with the databases of most other toxicants, the 

basic toxicological database for DE is substantial."81 The fact that components of DE 

are carcinogenic and mutagenic strongly suggests that inhalation of DE can lead to 

cancer, but it does not prove it. Thus, one important goal of research on DE is to 

determine whether the carcinogens and mutagens in DE are bioavailable and are taken 

up by the body in ways that cause cancer. 

The animal research 

Inhalation exposure to high concentrations of DE (4-10 mg/m3) has produced lung 

tumors in rats with some consistency. Sub-chronic inhalation exposure has also 

produced cancer in rats, but with less consistency. Evidence from rat studies in which 

DE extracts were instilled in the trachea, painted on skin and injected subcutaneously 

support the findings of the inhalation studies. The number of studies is large, however, 

and many studies did not produce a significant cancer response. Interpreting this body of 

work brings up complex issues, particularly with respect to the mechanism and the 

dose/response relationship. Despite the uncertainty, the US EPA and the California 

14 
OEHHA have both concluded that chronic exposure to high concentrations can lead to 

cancer in rats. EPA8 2 provides an exhaustive review of the rat data, and the California 

OEHHA provides a more concise one. 8 3 

The studies of mice do not provide a clear picture of the cancer response to DE. 

Pepelko et. al. 8 4 and Heinrich et. al. 8 5 produced significantly increased incidence of lung 

tumors in mice with inhalation of DE. Two other studies led by Heinrich (on the same 

mouse species) produced conflicting results. 86,8 7 Still other studies did not produce 

statistically significant cancer responses in mice, and at least one of these studies 

replicated the conditions under which tumors were produced in rats. 

None of the four extant hamster studies reports a significant cancer response to DE, and 

other work has also shown hamsters to be relatively insensitive to lung tumors. A small 

amount of work on cats and monkeys is inconclusive. 

Thus, the bulk of the animal evidence for carcinogenicity comes from the rat data, with 

the data on mice providing supporting, but equivocal, evidence. Important questions 

remain about the mechanism and the dose/response relationship in the rodent cancer 

response. First, rats have also been shown to develop tumors from high concentrations 

of particulates without the adsorbed organics found in DE (e.g., carbon black).88 These 

findings have given rise to a "lung-burden" theory of the cancer mechanism. This is the 

idea that high concentrations of particulate matter overwhelm the rodent's lung clearing 

capacity and the resulting particulate burden damages tissues, leading to a cell 

proliferation (cancerous) response. 

However, other work indicates that whole DE (including the organic mutagens) is more 

carcinogenic than DPM stripped of the organics. Rittinghausen et. al. instilled 15 mg of 

whole DE in the trachea of rats and found a 17-percent incidence of tumors compared to 

a 2-percent incidence in rats instilled with extracted DPM (no organics).89 Iwai et. al. also 

found that whole DE was more carcinogenic than DPM stripped of its organics (a 31-

percent tumor rate versus 14 percent on a lung burden basis). Studies by Gimmer et. al. 

specifically implicate the PAHs in DE. In this work, DE extracts were separated into 

PAH-laden and PAH-free fractions, and the extracts were implanted in rat's lungs. The 

fraction with PAHs produced a 25-percent tumor rate, and the fraction without PAHs 

produced no tumors.(cite) These studies and others suggest that whole DE is likely to be 

more carcinogenic than an equal amount of particulate matter without the organic 

mutagens. Further, by showing that the organics in DE can be both bioavailable and 

carcinogenic in rodents, this work leaves open the possibility of mutagenic activity at 

much lower concentrations. More work exploring this possibility is needed. 

Recently, a third hypothesis has emerged regarding the carcinogenicity mechanism in 

rodents. Macrophages and lymphatic cells in several rodent species produce elevated 

levels of oxidant reactants when challenged by foreign particles. Under certain 

circumstances these oxidant reactants can initiate a process that can damage DNA.90 

Ongoing research is focused on determining whether this process can translate fine 

particulate exposure into lung tumors in rodents. 

Thus, while the evidence for a cancer response in rats is sufficient, the mechanism is 

uncertain, and this adds to the uncertainty about the dose/response relationships. The 

"particle-burden" theory and, to a lesser extent, the "oxidant reactant" theory imply a 

dose/response relationship. That is, more particles in the lung increase the risk of 

cancer. In contrast, the organics in DE, which are carcinogenic at high concentrations, 

may also be carcinogenic at low concentrations. Notably, while DE constituents like 

15 
benzene are known carcinogens, thresholds have not been identified for their 

carcinogenic effects. 

The truth about the cancer mechanism in rats may not be simple. It seems probable that 

more than one mechanism exists, and more than one may be involved in any given 

cancer response. 

The epidemiological data 

The evidence from epidemiological studies is considered strongly supportive of a finding 

that DE is "causally related" to lung cancer, although there are considerable 

uncertainties within this body of work. The literature consists primarily of three study 

types: population-based case-control studies of lung cancer and cohort and case-control 

studies of workers in selected industries. These studies generally focus on the risks of 

chronic exposure to DE; thus we provide a very brief review of this work. 

The general population-based, case-control studies review the occupational history of 

cancer patients and compare these data to that of a control group. As a whole, these 

studies, all of which control for cigarette smoking, have consistently found increased 

incidence of cancer in truck drivers, railroad workers, heavy equipment operators and for 

self-reported diesel exposure in general.91 

The occupational studies identify workers in positions likely to be chronically exposed 

and determine whether there is increased lung cancer within this group relative to the 

general population. These studies, not all of which control for smoking, have consistently 

identified statistically significant elevations in lung cancer rates. Important studies 

include examinations of truck drivers, garage mechanics and railroad workers.92 Among 

the most influential studies have been the studies of railroad workers performed by 

Garshik et. al. 93,9 4 and the studies of truck drivers performed by Steenland et. al. 95,9 6 

Although these studies identify consistently elevated incidence of cancer among 

exposed populations, there are significant uncertainties associated with the findings. 

First, few of the studies measured the exposure of the workers; rather they 

reconstructed exposure retrospectively. Second, in many of the studies there is 

insufficient control for potential confounding factors, such as smoking. Despite these 

uncertainties, several meta-studies of the epidemiological literature have concluded that 

there is an association between chronic exposure to DE and lung cancer. 

In 1995 the Health Effects Institute reviewed over 30 studies and found a weak but 

relatively consistent association between exposure and lung cancer.97 HEI concluded 

that occupational exposure to DE from diverse sources increases the rate of lung cancer 

by 20 to 40 percent in exposed workers generally, and to a greater extent among 

workers with prolonged exposure. HEI also found that the results are not explicable by 

confounding caused by cigarette smoking or other known sources of bias. In 1998 the 

California OEHHA also reviewed 30 studies and found that all but five of them reported 

at least one positive association between diesel-related occupations or exposure and 

lung cancer, although some were not statistically significant.98 

The California ARB's interpretation of the data 

In 1998, after an exhaustive review of the available data, the California ARB concluded 

that diesel exhaust is a known carcinogen and issued a unit risk number for chronic 

exposure. The ARB based this finding on the weight of evidence found in the 

epidemiological, animal and toxicological literature combined. Regarding the 

epidemiological work, the ARB noted that more than 30 studies are consistent with an 

16 
association between diesel exhaust and lung cancer. A key factor in the ARB's 

assessment of these data was the meta-analysis of the epidemiological literature 

performed by the California OEHHA (discussed above), which found that "statistically 

significant pooled estimates of relative risk persisted through numerous subset and 

sensitivity analyses." 9 9 The ARB viewed the animal and toxicological data as consistent 

with the epidemiological data and supportive of a causal association. In particular, the 

ARB cited the rat studies and the work showing that constituents of diesel exhaust are 

mutagenic and carcinogenic. 

Based on the epidemiological data, the ARB established a lifetime risk figure of 3 x 10~4 

per ug/m3, or 300 additional cancer deaths per million people per pg/m3. This figure 

represents the additional cancer risk from chronic exposure to diesel exhaust over a 70-

year lifetime. Based on estimated average levels of DE in the state (averaged over both 

indoor and outdoor areas) of 1.54 pg/m3, this represents roughly 450 cancer cases per 

million Californians due to DE. However, this assessment of chronic risk may have little 

relevance to the risks from acute and sub-chronic exposure. Regarding shorter term 

exposures, the ARB noted only that that they had not identified a threshold for the 

carcinogenic effects of DE. 

EPA's interpretation of the cancer data 

EPA released its comprehensive Health Assessment Document for Diesel Engine 

Exhaust iri May of 2002. Based on the body of evidence from human, animal and other 

studies, this assessment concludes that diesel exhaust is "likely to be carcinogenic to 

humans by inhalation and that this hazard applies to. environmental exposure 

conditions." EPA bases this decision on the following evidence: 

• Strong but less than sufficient epidemiologic evidence for a causal association 

between DE exposure and increased risk of lung cancer among workers in 

different occupations; 

• Evidence of carcinogenicity of DPM in rats and mice by noninhalation routes of 

exposure (intratracheal instillation, lung implantation, skin painting, and 

subcutaneous injection); and 

• Extensive supporting data including the demonstrated mutagenic and/or 

chromosomal effects of DE and its organic constituents, suggestive evidence for 

the local and systemic bioavailability of the organics from DE, and knowledge of 

the known mutagenic and/or carcinogenic activity of a number of individual 

organic compounds present on the particles (e.g., PAH and derivatives) and in 

the DE gases (e.g., benzene, 1,3 butadiene, and aldehydes). 1 0 0 

The agency notes that the evidence for a hazard is strengthened by the fact that 

concentrations of diesel exhaust commonly found in the environment are close to, if not 

overlapping, the occupational exposures examined in these studies. Due to the high 

concentrations used in the rat inhalation studies, EPA does not find these data predictive 

of a human hazard at lower environmental responses. 

EPA does not derive a cancer unit risk estimate in the Health Assessment Document, 

but they do provide a detailed discussion of the available data on the dose-response 

relationship of the cancer endpoint and the uncertainties in those data. 1 0 1 

EPA does not state whether its finding that DE is. a probable carcinogen applies to both 

chronic and. acute exposures, and this is consistent with the uncertainty around the 

mechanisms of the cancer response and the dose/response relationships. Based on the 

17 
existing literature, EPA concludes that there may not be a threshold for cancer effects. 

Charles Ris of EPA writes, "in the absence of a more complete understanding of how 

diesel exhaust may cause adverse health effects in humans and laboratory animals, 

related assumptions (i.e., the presence of a biological threshold for chronic respiratory 

effects based on cumulative dosage and the absence of a threshold for lung cancer 

stemming from subtle and irreversible effects) are considered reasonable and 

prudent." 1 0 2 

Regarding the issues of mechanism and threshold, EPA writes: 

The particle overload hypothesis appears sufficient to account for DE-induced lung 

cancer in rats. However, there is also biological plausibility for lung cancer induction in 

humans at concentrations insufficient to induce lung particle overload as seen in rats. 

The uptake of particles by epithelial cells at ambient or occupational exposure levels, 

DNA damage resulting from oxygen-free radicals generated from organic molecules, and 

the gradual in situ extraction and activation of procarcinogens associated with the diesel 

particles may play a role in this response and provide a basis for the plausibility. The 

slower particle clearance rates in humans (up to a year or more) may result in greater 

extraction of organics. This is supported by reports of increased DNA adducts in humans 

occupationally exposed to DE at concentrations unlikely to induce lung particle 

overload. 1 0 3 

VI. Conclusion s 

There is strong evidence that acute and sub-chronic exposure to moderate levels of DE 

results in non-cancer health effects. DE also contains known mutagens and 

carcinogens, and these chemicals represent a plausible mechanism for cancer resulting 

from acute and sub-chronic exposure. However, there is considerable uncertainty 

around the potential for cancer from non-chronic exposure. DE also contributes to urban 

smog, which poses health risks to asthmatics and other subgroups. However, smog is a 

regional problem, caused by pollution from many different sources, and diesel 

generators are a relatively small source of smog precursors. Thus we do not address the 

health effects of smog here. 

In a number of laboratory tests, healthy humans have been exposed to moderate levels 

of DE, in the range of 100 to 300 pg/m3 of diesel particulate matter ("DPM"). (DPM is 

commonly used as a surrogate measure of whole DE.) Consistently observed symptoms 

include coughing, wheezing and eye and nose irritation. Dizziness, nausea and other 

neurological symptoms can result from exposure to higher concentrations. DE has also 

been shown to exacerbate existing allergies. In addition to these symptoms, exposure to 

DE results in well documented inflammatory and immunological responses at the cellular 

level in both the respiratory and cardiovascular systems. A considerable body of animal 

research provides additional information about this inflammation/immune response. 

Exposure to DE may pose much more serious risks, however, to people with lung and 

heart disease. Epidemiological studies have established a clear link between exposure 

to urban fine particulate matter and daily illness and mortality from lung and heart 

disease. Work is ongoing to understand the mechanisms underlying this association and 

the specific particles at cause, but it appears that the cellular responses to particulate 

exposure include mechanisms that can cause acute respiratory and cardiac distress and 

death. Two facts suggest that DE plays a significant role in the dynamic. First, diesel 

particulate matter makes up a significant portion of ambient fine particulate matter in 

many of the urban areas studied. Second, although there are associations with several 

pollutants, the strongest association is between fine particulates and daily health effects, 

18 
and over 90 percent of the particulate matter by mass in most DE is fine particulate 

matter. 

The research on DE exposure and cancer has yielded less certain conclusions. There is 

reasonably strong epidemiological evidence that chronic exposure to DE (usually studied 

in an occupational setting) leads to lung cancer. Chronic exposure to high 

concentrations has also been shown to produce lung tumors in rats. Based largely on 

the epidemiological data, the US EPA has labeled DE a "probable" carcinogen, and the 

California Air Resources Board has labeled it a "known" carcinogen and established a 

unit risk number for chronic exposure. However, these findings may tell us little about 

whether shorter-term and more periodic exposure to DE can cause cancer. 

The strongest evidence that short-term exposure could lead to cancer lies in the known 

carcinogens and mutagens within DE. These chemicals include benzene, formaldehyde, 

acetaldehyde, acrolein and PAHs. Importantly, there is no known threshold for the 

carcinogenicity of some of these chemicals (e.g., benzene). However, more work needs 

to be done to determine whether these chemicals produce cancer in the case of 

inhalation exposure to DE. Currently, the weight of evidence suggests that longer 

exposure periods are more likely to lead to cancer than shorter ones, but that the 

potential for cancer resulting from shorter-term exposure, via a non-threshold, mutagenic 

mode of action, cannot be ruled out. 

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9 6

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with lung cancer. American Journal of Industrial Medicine 21:887-890. 

9 7

 Cohen AJ and Higgins MWP. 1995. Health effects of diesel exhaust: Epidemiology, Diesel Exhaust: A 

Critical Analysis of Emissions, Exposure and Health Effects. A Special Report to the Institute's Diesel 

Working Group, Health Effects Institute, Cambridge MA. 

9 8

 California EPA. 1998. p. C-1 - C-29. 

9 9

 California EPA. 1998. p. 1-8. 

1 0 0

 US EPA. 2002. p. 7-142. 

1 0 1

 US EPA. 2002. 

1 0 2

 Ris, Charles, 2002, p. 36. 

1 0 3

 US EPA. 2002. p. 7-137. 

23 
MICROPOWER AT 

THE CROSSROADS 

Public Health and the Future 

of Distributed Generation 

MASSPIRG Education Fund 
MICROPOWER 

AT THE CROSSROADS 

Public Health and the Future 

of Distributed Generation 

Brad Heavner 

Frank Gorke 

MASSPIRG Education Fund 
ACKNOWLEDGMENTS 

The MASSPIRG Education Fund gratefully acknowledges Seth Kaplan of the Conservation Law Foundation and Todd Campbell of the Coalition for Clean Air for providing assistance in the development and drafting of this report. Thanks to Mara 

Thermos, Ellen Montgomery, and Marianne Zugel for research assistance. Thanks 

also to Michael Perri, Katie McCormack, and Rob Sargent for editorial guidance. Thanks 

to Harriet Eckstein for layout design. 

Cover photographs courtesy of (clockwise from upper left): Paul Gipe, High Frequency 

Active Auroral Research, National Renewable Energy Laboratory, and Capstone 

Microturbines. 

This report was made possible by the generous support of the Pew Charitable Trusts 

under their National Distributed Generation Emissions Campaign. 

The authors alone bear responsibility for any factual errors. The recommendations are 

those of the MASSPIRG Education Fund. The views expressed in this report are those 

of the authors and do not necessarily reflect the views of our funders. 

© 2003 MASSPIRG Education Fund 

The MASSPIRG Education Fund is a 501(c)(3) organization working on environmental protection, consumer rights, and good government in Massachusetts. 

For additional copies of this report, send $10 (including shipping) to: 

MASSPIRG 

29 Temple Place 

Boston, MA 02111 

For more information about the MASSPIRG Education Fund, please call 617-292-

4800 or visit the MASSPIRG web site at www.masspirg.org. 
TABLE OF CONTENTS 

Executive Summary 4 

What Is Distributed Generation? 7 

The Cleanest Micropower Technologies 11 

Solar Photovoltaics 11 

Wind 12 

Fuel Cells 14 

Combined Heat and Power 16 

The Dirtiest Micropower Technologies 18 

Diesel Generators 18 

Other Fossil Fuel Internal Combustion Engines 22 

Improving Engines for Emergency and Portable Use 23 

New Micropower Technologies 25 

Alternative Fuel Reciprocating Engines 25 

Turbines 25 

Microturbines 25 

Stirling Engines 26 

Policy Recommendations 28 

Appendix A: Alternative Fuels 30 

Appendix B: Glossary 31 

Notes 33 
EXECUTIVE SUMMARY 

T

he debate over Massachusetts' energy future has focused increased 

attention on micropower, the generation of electrical energy by homeowners and businesses near the place it is 

used as an alternative or supplement to 

the statewide power grid. 

Micropower, also known as distributed 

generation (DG), is a growing sector of 

the energy market that holds great promise for locally controlled power generation. 1

 Having facilities widely dispersed 

increases reliability, and some of these 

technologies are among the most environmentally friendly electricity generating technologies ever invented. But 

continued reliance on other types of 

micropower, technologies that are highly 

polluting, poses a threat to public health. 

Currently, micropower is not subject 

to the same air pollution controls as central power plants, and the most prevalent 

form of micropower currently in operation is also the most polluting form - diesel engines. These generators have been 

installed outside many public buildings 

and advertised for home use as a solution 

to the "energy crisis." 

As micropower has grown, policy makers have come to realize that limits on 

emissions from micropower facilities are 

needed to avoid the cumulative effects of 

many small but very dirty generators. And 

states increasingly recognize that they can 

increase energy generation flexibility and 

realize major environmental improvements by encouraging the cleanest forms 

of micropower. 

The Massachusetts Department of 

Environmental Protection (DEP) is planning to set air pollution standards for 

micropower technologies. They are seeking to establish a technology-neutral standard for all applications that works to 

reduce environmental emissions and protect public health. 

The DEP should set strict standards 

that fully protect human health and the 

environment, and should phase them in 

over time to allow manufacturers to prepare for change. New standards should 

encourage clean technologies such as solar and wind, allow developing technologies such as fuel cells and microturbines 

to gradually decrease emissions, and prohibit or dramatically reduce use of the 

most polluting technologies. Due to severe environmental and public health 

impacts from the growing use of diesel 

generators, emissions standards must be 

set at levels that limit diesel applications 

to emergency situations and only when 

generators are operated in conjunction 

with emission-control measures. 

Micropower is at a crossroads. New standards should promote clean technologies, 

not allow dirty technologies to proliferate 

and pollute the air. And standards need to 

establish uniform treatment of the various 

micropower technologies and applications. 

We have produced this report to point 

the way to a clear future direction. As we 

work to promote the highest possible 

level of efficiency in our use of energy, 

we must simultaneously support sustainable, reliable, versatile technologies that 

can bring efficient energy generation 

right to the source of use while reducing 

harmful air pollution. 

Policy Recommendations 

Principles 

To ensure that public health is protected 

and new technologies that reduce pollution are encouraged, distributed generation policy should be based on the 

following principles: 

o Micropower must be as clean as or 

cleaner than the cleanest central 

4 Micropower at the Crossroads 
power plant technology currently in 

widespread use. 

o State rules and incentives must 

promote the cleanest energy industry 

for the future of iMassachusetts. 

o Regulations should be as simple as 

possible so manufacturers can 

anticipate changes and comply with 

new technology requirements. 

Primary Recommendations 

State agencies can help move micropower 

in the right direction. To protect the 

health of the people of Massachusetts and 

the air quality of the state while helping 

to assure reliable local power generation, 

we recommend the following immediate 

policy actions: 

o Set stringent emissions standards for 

all micropower units operated in 

Massachusetts. Use output-based 

standards to encourage greater 

efficiency of performance. 

o Conduct a comprehensive inventory 

of existing micropower and other 

on-site generation. 

o Streamline the permitting process for 

clean units that meet or beat new, 

stringent standards. 

o Ensure aggressive enforcement of 

standards and establish significant 

penalties for violation. 

Additional Recommendations 

In addition, many other specific policies 

could advance clean micropower while 

curbing the use of dirty micro-power. We 

recommend that state agencies: 

Establish standards and rides for 

jnicropower operation: 

• Require that all micropower units 

operated in Massachusetts receive 

certification or permits as a condition 

for being connected to the electric 

grid. 

• Require that transmission grid 

operators draw on clean, efficient 

micropower before similarly priced 

dirty generation facilities. 

• Require emissions control measures 

for diesel generators used for emergency back-up power supply. 

• Require that all new residential and 

commercial construction be "solarready" with the basic infrastructure 

to ease future installation of photovoltaic panels. 

Provide funding for clean micropowei~. 

• Require formal consideration of 

clean micropower as a potential least 

cost alternative to transmission and 

distribution upgrades and a means of 

avoiding the cost of future environmental regulation. 

• Expand funding for clean micropower technology advancement. 

• Expand the availability of financial 

incentives, including financing 

assistance, buy-down programs, tax 

credits, and grants, for the installation of clean micropower. 

• Provide incentives for developers to 

include clean micropower at new 

residential or commercial construction projects. 

• Provide incentives for the trade-in 

and upgrade of polluting micropower 

installations. 

Clear hurdles to the implementation of 

clean micropower: 

• Streamline the permitting and utility 

interconnection process for clean 

micropower installations. 

• Develop incentive tariffs and reduced 

standby and exit fees for clean 

micropower installations. 

Micropower at the Crossroads 5 
The adoption of these recommendations will promote a vital distributed 

generation system that reduces the 

negative public health impacts associated 

with diesel and other dirty micropower 

technologies. 

6 Micropower at the Crossroads 
WHAT IS MICROPOWER? 

F

or more than a century the standard 

formula for generating and distributing electricity has been simple. 

Build a huge power plant and run power 

lines to population centers where industry and people need the electricity. Connect the individual home or business to 

the electrical grid and power up. 

Primarily using fossil fuels, these facilities have grown in scale and quantity 

as our demand for electrical power has 

increased. Many of these giant power 

plants have been major polluters as they 

have worked to provide a cheap, reliable 

electricity source for consumers. Despite 

advances in technology, these large central power plants continue to dominate 

our energy system in size, environmental consequences, and convenience. 

The dominance of this model has facilitated the proliferation of electrically 

powered devices to the point where most 

of us never think about how power is generated. We just plug our computer into 

the wall outlet and get to work. 

In some cases it has been advantageous 

to develop localized power generating 

capacity. Geographically isolated facilities 

and some large factories have been using 

local power generation for years, frequently deploying many of the technologies that cause environmental harm. But 

it was a rare occurrence when an individual would need or want independent 

local power generation for a home or 

small business. 

Deregulation of the electric power 

production industry and the recent turmoil in energy markets has started to 

change all that. With growing concerns 

about the reliability of traditional power 

sources due to increases in power plant 

down time, more and more consumers 

are questioning the conventional model 

of central power plants. They are looking for more reliable energy sources, 

searching for greater control over power 

costs, and seeking alternatives to power 

sources that degrade the environment and 

undermine public health. 

The combination of advancing technology and widespread concerns about 

large central power plants has made localized power generation an idea whose 

time has come. Instead of concentrating 

power sources at large plants, micropower systems locate power sources 

closer to the consumer - in an office 

building, a neighborhood, a factory, or a 

home.-

For many, small power generation 

units located near the point of use have 

been a safety and reliability measure to 

supply back-up power during blackouts. 

Others have suggested that in light of 

escalating energy costs during peak demand periods, micropower can be used 

as a cheaper alternative power source or 

a source of profit by selling the distributed power into the grid. 

In grid-congested areas where transmission line upgrades would otherwise be 

needed, micropower has the potential to 

significantly reduce costs for power. 

Transmission and distribution costs can 

reach $1.50 for every $1.00 spent on electricity generation.3

 In addition, society 

can benefit through enhanced reliability 

and decreased need for infrastructure. 

Estimates of the monetary value of these 

benefits range as high as 2.8 (t/kWh. This 

Table 1: The Economic Benefits 

of Decentralized Power (C/kWh) 4 

Benefit Savings 

Substation deferral 0.16-0.6 

Transmission system losses 0.2-0.3 

Transmission wheeling 0.28-0.71 

Distribution benefits 0.067-0.17 

Enhanced reliability 1.0 

Total 1.7-2.8 

Micropower at the Crossroads 
is a substantial savings from current generating and distribution costs, which are 

now typically 4-9 c/kWh. 

Growing interest in local control of 

electrical power generation is both an 

opportunity for and a threat to Massachusetts residents. The central power 

plant system has evolved some cleaner 

technologies, but older, dirtier micropower technologies are still predominant. 

We cannot allow the proliferation of localized power generation to undermine 

pollution standards. 

The affordability of meeting stricter 

emissions standards was documented in 

a 2002 study by Energy Nexus Group 

analyzing the economic feasibility of 

complying with proposed new standards 

for micropower in California. The study 

found that with the amount of technology advancement expected under normal 

market forces, nearly all of the cleanest 

technologies will meet the standards in 

2003, most of the new technologies will 

meet the standards in 2007, and all but 

the dirtiest technologies will meet the 

standards in 2012. The study determined 

the cost of adding emissions control 

equipment to fossil fuel-based micropower to be only about 1 c/kWh. 5 

As public agencies consider regulations 

addressing micropower technologies, we 

have the opportunity to promote costeffective renewable energy sources that 

are significantly less harmful to our 

health. But if the growing demand for 

micropower results in the proliferation 

of polluting technologies, we face the 

prospect of higher levels of localized 

emissions that place our respiratory 

health at significant risk. 

What follows is an overview of the 

pollution and public health impacts of 

many of the technologies currently available to those interested in the deployment 

of micropower. We have grouped the 

various technologies into three categories based on their current environmental performance. New regulations should 

be performance-based, so that emerging 

technologies have equal opportunity to 

meet emissions standards in the future. 

Clean Micropower - The cleanest 

distributed generation technologies, 

primarily using renewable fuel 

sources. These include solar, wind, 

and fuel cells. These forms of power 

generation have minimal negative 

public health impacts. In addition, 

Figure 1: Emissions from Micropower Technologies6 

25 

5 20 

o 

15 

E 10 

Diesel Natural Gas Natural Gas Microturbine 

Engine Engine Engine 

(lean burn) (rich burn) 

Fuel Cell 

NOx • CO 

ED SOx 

PMIO 

H UHC 

Solar Wind 

8 Micropower at the Crossroads 
Figure 2: Carbon Dioxide Emissions from Micropower Technologies7 

1,800-I 

1,600-

MIAI

1,400 • 

, 

1,200-

1,000 -

t o 

C 800 -

o 

(/) 600 -

E 

LlJ 400 -

200 -

Diesel Natural Gas 

Engine Engine 

(lean burn) 

Natural Gas 

Engine 

(rich burn) 

Microturbine Fuel Cell Solar Wind 

high-efficiency combined heat and 

power systems can significantly 

reduce negative impacts. 

Dirty Micropower - The dirtiest 

and best-known technologies, using 

fossil fuel sources. Diesel generation 

is the most prevalent technology, but 

there are also gasoline and natural 

gas engines that are excessively 

polluting. These forms of power 

generation undermine public health 

and cause disease. 

New Micropower Emerging 

technologies have the potential to 

deliver cleaner power. Options such 

as alternative fuels and microturbines hold promise for the future. 

The health impacts of these forms of 

power generation vary. 

On-site power generation in itself is 

no panacea for the problems plaguing the 

energy market. If the rush to micropower 

is a rush to the most available and least 

expensive technology, then some of the 

problems - including increased pollution, 

inefficient energy production, costs tied 

to non-renewable fuels, and growing public health problems - will be perpetuated. 

The technology is available to avoid 

those pitfalls and to promote efficient and 

increasingly cost-effective micropower 

that can benefit the environment, the reliability of the electricity system, and public health. Some of the potential advantages 

of clean micropower include: 

• Power doesn't have to travel long 

distances over the grid, reducing 

energy loss and the need to build 

new power lines. 

• Wind and solar technologies are 

fueled by renewable energy sources. 

• Generation at point of use allows for 

the utilization of waste heat for other 

energy needs. 

• Local generation can enhance the 

reliability of the electricity system by 

reducing the burden on the grid. 

• Fewer large, central-station power 

plants will be needed as micropower 

increases. 

• The potential for large-scale blackouts is reduced. 

• Local control of energy sources 

allows increased responsiveness to 

local concerns. 

• Power sources can be built to appropriate scale for local consumption. 

Micropower at the Crossroads 9 
The vast majority of micropower units 

currently operating in Massachusetts are 

diesel generators. Diesel generators release as much as 363 times more smogforming pollutants than the most efficient 

natural gas power plant technologies.8 

These pollutants have been shown to 

increase the risk of serious health 

problems ranging from headaches and 

nausea to asthma complications and lung 

cancer.7 

The opportunity to end this threat to 

public health is at hand if we use emission standards and policy incentives for 

distributed generation to push newer 

technologies to the forefront. 

10 Micropower at the Crossroads 
THE CLEANEST MICROPOWER TECHNOLOGIES 

S

olar and wind technologies have 

been proven effective for local 

power generation throughout the 

country. With free fuel, advanced technology, and incentives provided by the 

state, these technologies are becoming 

more cost effective and cost competitive.10 

Recently the power industry has made 

substantial advances in fuel cell technologies and in using combined heat and 

power systems to increase energy efficiency. Public agencies, small and large 

businesses, and individual homeowners 

are taking advantage of these advancements to install localized and independent power generation capacity. 

These clean technologies are not without their environmental impact, but they 

substantially reduce the environmental 

impacts of electricity generation. 

Solar Photovoltaics 

Many people mistakenly believe that solar power can only be harnessed effectively in the Southern and Southwestern 

states, but solar PV is a valuable resource 

for Massachusetts as well. The state's solar potential is excellent, and solar power 

generation peaks at the same time that 

energy demand peaks - in the heat of 

summer afternoons. 

Photovoltaic technology converts sunlight directly into electricity without using any moving parts. The basic building 

block is the photovoltaic cell, which is 

made of semiconductor materials. Cells 

can be connected together to form modules, and modules can be connected to 

form arrays. A few PV cells will power a 

hand-held calculator, while interconnected arrays can provide electricity for 

a remote village or serve as a power plant 

for a city. PV is a truly unique technology 

with many advantages. According to the 

U.S. Department of Energy, "it is easy to 

foresee PV's 21 st century preeminence."'' 

Although PV panels only generate 

electricity when the sun is shining, connection with the grid makes it possible 

to depend on PV, both from the consumer and the state planning perspectives. On hot days, when electricity 

consumption is at its peak, PV panels feed 

excess electricity into the grid. In the 

evening when the sun is down and electricity demand is lower, customers draw 

electricity from the grid. Recent improvements in "net metering" - in which the 

electricity meter runs backward when 

power is beingfed into the grid -have made 

this much more practical for consumers. 

Advantages of Photovoltaic 

Technologies 

• Simplicity - With no moving parts, 

operation and maintenance costs are 

minimal. 

• Versatility - PV can connect to the 

existing infrastructure of the utility 

grid and serve as an alternative 

power source during peak periods of 

power demand or it can operate 

remotely (off the utility power-line 

grid). Many PV systems are easily 

transported. PV can also be scaled 

according to the amount of power 

needed. 

• Reliability - First developed for U.S. 

man-made satellites in the 1950s -

where low maintenance was an 

absolute necessity - and now with 

over 40 years of technical advancements improving performance, PV 

has very high online availability.12 

Micropower at the Crossroads 
• Peak Output - PV power output 

peaks when demand peaks. 

• Quiet - PV systems make no noise. 

• Sustainability - PV shares the two 

advantages common to all renewable 

energy sources: it has a low environmental impact (it is nonpolluting) 

and the fuel is free. 

Solar PV has zero operating emissions. 

Therefore, solar PV is exempt from all 

air quality permitting requirements. 

Wind 

Wind turbines are an excellent local 

power generation option for many Massachusetts residents and businesses. A 

wind turbine consists of a rotor, an electrical generator, a speed control system, 

and a tower. When the wind blows and 

spins the propellers of the turbine, which 

are akin to airplane propeller blades, the 

kinetic energy of the wind is converted 

to mechanical power, which in turn drives 

the electrical generator and produces an 

electrical current. 

PV IN CAMBRIDGE 

ravestar, a Cambridge real estate developer that owns and operates 

shopping centers, installed a 20 kW photovoltaic array in 1999 as 

part of a $13 million redevelopment project at the Porter Square 

Shopping Center in Cambridge. 

The Porter Square project included the renovation of an existing strip 

mall with an addition that houses a pharmacy and health-fitness center. The 

20 kW photovoltaic array, consisting of 80 ASE 300 DGF/50 modules, was 

installed on top of the existing structure. 

The annual energy production of22,000 kWh of energy is applied to site 

lighting and common areas. This leads to annual savings of approximately 

$2,200. The system also offsets approximately 31,000 pounds of C02, 160 

pounds of S02, and 50 pounds of NOx each year.13 

The panel location, 

along the south front with 

a 3 5 degree tilt, makes the 

system more visible from 

the street and parking areas in order to increase its 

educational value. 

The shopping center 

also has an educational 

kiosk in the common area. 

Using a touch screen, visitors can find valuable information about how the 

system works, how much 

energy is produced, and 

other photovoltaic facts.14 

Micropower at the Crossroads 
Most people, are familiar with these 

turbines when they are grouped together 

in a wind farm and operate like a conventional power plant, feeding electricity to the utility grid. But small turbines 

can be installed and operated individually to satisfy the electrical needs of a 

home or business, just as they were on 

farms for hundreds of years. 

Individual turbines vary in size, ranging from about 30 feet high with propellers between 8 and 25 feet in length to 40 

stories high with propellers over 300 feet 

in length.13 

Single home-sized wind turbines in the 

10-50 kW range are becoming more 

popular in many places. Since they don't 

need as much wind as the larger turbines, 

they can be effective in more areas. 

Advantages of Wind 

Technologies 

• Simplicity - Operation and maintenance costs are minimal. Modern 

wind turbines require maintenance 

checks only once every six months.16 

• Versatility - Wind turbines can 

connect to the existing infrastructure 

of the utility grid or can operate 

remotely (off the utility power line 

grid). 

• Reliability - Wind power is the 

fastest growing energy source worldwide and its proven reliability has 

much to do with its success.17 Small 

wind systems are designed to operate 

for at least 30 years.18 

• Sustainability - Wind-generated 

power shares the two advantages 

common to all renewable energy 

sources: it has a low environmental 

impact (it is nonpolluting) and the 

fuel is free. 

• Quiet - Modern wind turbines are 

much quieter than combustion 

turbines. 

WIND POWER IN HULL 

T

he town of Hull recently 

turned to wind power, 

embracing its past while 

moving forward into a clean future. The town, 20 miles southeast of Boston on a peninsula 

between the Adantic Ocean and 

Boston Harbor, installed a 660 

kW Vestas V-47 wind turbine in 

2001 on a site that was home to 

a windmill long ago. The 150-

foot white tower, with 90-foot 

blades, is now the largest wind 

turbine on the East Coast.19 

The turbine supplies enough 

energy to power the town's 1,000 

streetlights and 14 traffic lights. 

This alone saves the local taxpayers $60,000 a year.20 

The turbine produces approximately 1.5 million kWh per 

year, the equivalent of supplying 

power to 200-250 homes.21 

The town is one of 18 recipients of the U.S. EPA's Environmental Merit Award in 2002. 

Hull was selected from a pool of 

90 nominations that year. This 

award, which has been given out 

since 1970, honors specific individuals or communities that 

demonstrate a strong commitment to 

Micropower at the Crossroads 13 
Wind technologies have many of the 

same advantages as solar photovoltaic 

technologies. Like solar PV, wind has 

zero operating emissions. Wind turbines 

are therefore exempt from all air quality 

permitting requirements. 

Fuel Cells 

Where solar photovoltaics or wind turbines are not feasible, fuel cell technologies are a good local power generation 

option, especially when operated in combined heat and power applications. (See 

below for more about combined heat and 

power.) Although they now use fossil fuels to create hydrogen, fuel cells emit far 

less pollutants than diesel and most other 

fossil fuel generators. Emissions from 

current cells are primarily C02 and water. With further development they will 

be able to utilize renewable energy to 

produce their hydrogen fuel. 

Through the chemical reaction of 

combining hydrogen and oxygen to make 

water, fuel cells convert chemical energy 

into electricity and heat without combustion. They operate similarly to batteries. 

Both batteries and fuel cells utilize an 

electrolyte separated by an anode and a 

cathode to generate a direct electrical 

current, and both can be combined into 

groups to increase power output. 

Batteries store their fuel, then periodically run down and require recharging. 

Fuel cells, on the other hand, are fed a 

continuous supply of fuel. The varying 

types of fuel cells all rely on hydrogen as 

their fuel, but they can get it from a variety of sources. 

Four different types of fuel cells - the 

Phosphoric Acid Fuel Cell (PAFC), the 

Molten Carbonate Fuel Cell (MCFC), 

the Proton Exchange Membrane (PEM), 

and the Solid Oxide Fuel Cell (SOFC) -

have been or are operating in 16 countries, and several more types are being 

developed and tested. 

Fuel cells are being developed for use 

in both vehicles and stationary applications. These applications include power 

for individual facilities such as hospitals, 

office buildings, and schools; primary 

power sources for remote villages and 

campgrounds; utility power plants; and 

power sources for temporary needs such 

as construction sites. As distributed electrical generation becomes more widespread, fuel cells could serve as primary 

power and thermal energy sources for 

virtually anything. 

Most fuel cells are named for their 

electrolyte, and they each have different 

properties, capabilities, fuel requirements, and emissions. For example, the 

PAFC that is commercially available today is offered in the 200 kW size, though 

it is technically able to operate in the 

range of 50 kW to 11 MW. The PAFCs 

in operation today use either natural gas 

or propane, but could also be fueled by 

methane, alcohols, landfill gas, or anaerobic digester gases. 

Because of the low emissions of fuel 

cells, Massachusetts has granted an exemption to PAFCs using natural gas from 

all air quality permitting requirements in 

the state. 

In the future, renewable energy 

sources may be widely used to generate 

the hydrogen needed to power fuel cells. 

Sunline Transit has a new hydrogen generation facility powered by wind and solar energyAdvantages of Fuel Cell 

Technologies 

• Low emissions - Fuel cells emit 

fewer pollutants than any other fossil 

fuel-based micropower technology. 

• Quiet-Fuel cells are quiet. 

• Versatility - Fuel cells are modular in 

design; so they can be stacked to 

increase power output. 

• Simplicity - With few moving parts, 

fuel cells are low-maintenance. 

14 Micropower at the Crossroads 
CAPE COD FUEL CELL 

C

ape Cod will soon be home to a fuel cell of the latest commercial 

technology at the Coast Guard Air Station in Bourne. The 250 

kW Direct Fuel Cell is expected to be installed by Fall 2 002.23 

The fuel cell will operate on natural gas. The energy produced will be 

used to heat water for station personnel both in the barracks and the galley; Facility managers hope that excess heat from the fuel cell will be used 

to heat the building in the future. The initial reduction in utility bills is 

projected to be $50,000 per year.24 

The fuel cell is projected to be 70% efficient, generating 230 kW for 

the first two years. In two years the plant's stack is scheduled for replacement in order to take advantage of newer technology. After that upgrade 

the plant is expected to generate 300 kW or more. 

Since the mission of the air station is search and rescue, it is particularly 

important to have power during heavy storms. The Coast Guard determined that the fuel cell would be the most dependable power source for 

that purpose. It will help support four H60 Jayhawk helicopters and four 

H25 Falcon jets.25 

The most significant feature of tfle Bourne facility is the use of a molten carbonate fuel cell. Molten carbonate fuel cells are a cutting edge fuel 

cell technology because they have been developed to capitalize on energy 

efficiency and essentially operate without generating pollution. The Bourne 

plant is among the first few of these cells 

to be installed in the United States.26 

This project is made possible by the 

joint effort and financial backing of both 

government and private business. The 

U.S. Department of Energy Technology 

Lab, the Massachusetts Renewable Energy Trust, and Keyspan Inc., a natural 

gas supplier, made it possible for PPL 

Spectrum and Fuel Cell Energy to create this plant. 

Photo by Fuei Cell Energy 

Flexibility - Fuel cells can use different fuel sources since they only need 

hydrogen and oxygen. 

Reliability - Fuel cells are online a 

greater percentage of the time than 

large power plants. 

Micropower at the Crossroads 15 
CHP AT MALDEN MILLS 

Photo by Maiden Mills 

M

aiden Mills, in Lawrence, is no stranger to the media spotlight. The 

mill first received attention in 1995 when a fire destroyed three of 

its buildings. CEO Aaron Feuerstein gained national acclaim when 

he decided to rebuild the company while keeping his employees on the payroll. 

Now Maiden Mills, manufacturer of Polartec fabric, is back in the news. 

The company was presented with a 2000 Energy Star Combined Heat & Power 

Certificate, sponsored by the U.S. EPA and the 

U.S. Department of Energy. The award is given 

to leaders who increase electric generation efficiency with the use of combined heat and 

power programs. 

When Maiden Mills began operating its new 

CHP facility in 1999, then-Secretary of Energy 

Bill Richardson was on hand to dedicate the facility, along with other dignitaries. Richardson 

said, "The cogeneration power system we dedi-

— » . cated today will produce energy for the factory 

'fc*1'^"*'] while virtually eliminating sulfur dioxide emis5

 sions, reducing nitrous oxide emissions by 75 

percent, and cutting carbon dioxide emissions 

by 25 percent. This will make Maiden Mills a 

model of energy efficiency and environmental responsibility."28 

Maiden Mills installed two 4.3 MW turbines, manufactured by Solar Turbines, which use fiber ceramic combustion liners. The liners were specifically 

developed to decrease NOx emissions by at least another 40%. The two turbines combine to produce enough energy to supply 4,000 homes with power.29 

The facility at Maiden Mills provides electricity for the plant. The mill 

maintains its connection to the Massachusetts Gas & Electric grid as a backup energy source in case of turbine failure. 

The cogeneration system was developed in partnership with the Department of Energy. 

Combined Heat 

and Power 

Combined heat and power (CHP) is not 

a specific generating technology but 

rather an application of technologies to 

meet end-user needs for heating or cooling as well as mechanical and electrical 

power. 

Recent technology developments -

particularly in turbines and microturbines - have made small-scale CHP 

systems more cost-effective and reliable. 

When properly designed, fossil fuelbased generators can dramatically increase their efficiency through 

modification into CHP systems. 

In CHP systems, the heat that is normally released as waste heat is instead 

recovered and used to heat water, rooms 

and buildings and/or drive motors for air 

conditioning or refrigeration. CHP systems 

16 Micropower at the Crossroads 
can also use waste heat to provide steam 

to generate more electricity, like "cogeneration" at large power plants. Combined 

heat and power systems can be employed 

in many commercial and industrial facilities where there is a relatively constant 

thermal need. 

Recovering and reusing waste heat in 

this manner can make generators more 

than 80% efficient, more than double the 

33% average efficiency of conventional 

electricity generating systems.27 The increased efficiency saves the extra fuel that 

otherwise would be necessary to operate 

heating systems - often replacing old, inefficient and dirty boilers. 

Increased fuel efficiency translates directly into reduced emissions of greenhouse gases and other pollutants. NOx, 

which forms smog, and C02, the principal global warming pollutant, are significantly reduced. Combined heat and 

power systems also reduce S02 emissions, precursors to acid rain, and particulate matter, a cause of chronic lung 

disease. 

Because it is still based on burning fossil fuels, CHP is not sustainable energy 

production on the level of wind and solar. But as long as fossil fuels are used to 

drive generators, CHP should be widely 

encouraged as a very good improvement 

over less efficient technologies. 

Advantages of CHP Systems 

• Efficiency - Increases efficiency of 

fuel use by capturing waste heat for 

heating, cooling and other on-site 

energy requirements. 

• Flexibility - Can be designed to 

deliver multiple energy services. 

• Reliability - Advanced technology 

and local control enhance service 

delivery. 

• Improved Environmental Performance - Produces lower emissions 

than conventional separate systems. 

Key Recommendations for 

Clean Micropower 

Electricity generation has always had serious negative impacts on air quality. We 

now have the opportunity, however, to 

generate our power with minimal environmental consequences. State agencies 

must do all they can to encourage the 

widescale implementation of clean technologies, as they simultaneously encourage energy users to consume energy as 

efficiently as practical. Recommended 

policy actions include the following. 

• Require formal consideration of 

clean micropower as a potential least 

cost alternative to transmission and 

distribution upgrades and a means of 

avoiding the cost of future 

environmental regulation. 

• Incorporate efficiency in emissions 

standards to credit the efficiency 

advantages of combined heat and 

power. 

• Expand the availability of financial 

incentives, including buy-down 

programs, tax credits, and grants, for 

the installation of clean forms of 

micropower. 

• Develop incentive tariffs and reduced 

standby and exit fees for clean 

micropower installations. 

• Streamline the permitting and utility 

interconnection process for clean 

micropower installations. 

• Expand funding for clean micropower technology advancement. 

• Provide incentives for developers to 

include clean micropower at new 

residential or commercial 

construction projects. 

• Establish requirements that all new 

residential and commercial 

construction be "solar-ready" with 

the basic infrastructure to ease future 

installation of photovoltaic panels. 

Micropower at the Crossroads 17 
THE DIRTIEST MICROPOWER TECHNOLOGIES 

T

he internal combustion engine 

(ICE), the traditional technology 

used in vehicles, is also the predominant technology for portable and 

stationary generators. Also called reciprocating engines, ICEs can use a variety 

of fuels, including diesel, gasoline, natural gas, and propane. Diesel is the most 

common fuel for ICEs used as micropower. 

Diesel Generators 

Although there are now many competitive technologies available for micropower, diesel generators have historically 

dominated the micropower market. This 

form of micropower has also been the 

most cost effective for consumers, largely 

because the public health and environmental costs of burning diesel fuel are not 

accounted for in the cost of generation. 

The diesel generator is also the most 

polluting form of micropower. Many 

people are familiar with the black plumes 

of smoke released by diesel- trucks and 

buses. Diesel generators are no different. 

The harmful health effects of diesel exhaust have been studied and well documented for decades. Because many diesel 

generators are located in dense urban 

settings, this technology significantly 

increases the public's exposure to cancercausing pollutants. 

Quantifying the Problem 

Diesel generators are widely used 

throughout Massachusetts, providing 

power for everything from businesses to 

agricultural equipment to homes. Diesel 

generators are found in the basements of 

office buildings or powering lights used 

during freeway construction. However, 

no accurate inventories of diesel generators have been made. 

The DEP maintains a database that 

includes electric generators called the 

Stationary Source Emission Inventory 

System (SSEIS). Facilities that burn more 

than 10 million Btu/hr of energy must 

register with this system, covering only 

the largest distributed resources. 

The SSEIS database contains records 

of 760 fossil fuel-based micropower units 

in Massachusetts. 77% of these are powered by diesel. (See Table 2.) 

Estimates based on data from other 

states indicate that this is likely to vastly 

understate the prevalence of diesel generators in Massachusetts. The California. 

Air Resources Board (CARB) has made 

the best attempt among state air quality 

agencies to quantify diesel generator 

ownership. CARB estimates that there 

Table 2: Fossil Fuel-Based Micropower Units Registered in Massachusetts1 

Fuel Number of 

Generators 

Emissions (tons/yr) Fuel Number of 

Generators NOx ; S02 PM 10 ' CO VOC 

Diesel/Oil 583 407 53 24 175 208 

Natural Gas 159 621 12 45 322 125 

Kerosene/Jet Fuel 4 <1 <1 <1 <1 <1 

Propane 9 <1 <1 <1 1 <1 

Gasoline 5 1 <1 <1 28 1 

Total 760 1,030 65 69 526 334 

18 Micropower at the Crossroads 
are a total of 65,382 diesel generators in 

California. Assuming an equal number of 

diesel generators per capita in Massachusetts, this equates to 5,638 diesel generators in the state. (See Table 3.) 

If all generators in the state emit pollutants at the same average rate as the 

actual average emissions of the generators in the SSEIS database, 5,000 diesel 

generators in Massachusetts would emit 

3,500 tons of NOx, 460 tons of S02, 200 

tons of PM10, 1,500 tons of CO, and 

1,800 tons of VOCs. While this is a rough 

estimate of statewide emissions based on 

an incomplete database, these numbers 

are large enough to indicate that diesel 

generators are a significant source of pollution that demand regulatory attention. 

Diesel generators are used in a variety of 

ways, with three general categories of use: 

Emergency standby generators -

Often referred to as "back-up generators" 

or BUGs, these are generators that operate on a temporary basis as back-up 

power supplies in the event of power outages. 

Prime generators - Generators used 

on a regular basis to supplement energy 

from the power grid. 

Portable generators - Generators 

that are moved from location to location 

to provide power (motor vehicles and engines used to propel equipment directly 

are not considered portable generators). 

The more hours a diesel engine operates, the more pollutants it releases 

into the air we breathe. For example, 

emergency back-up generators in normal operation are generally used only 

25-50 hours a year while prime engines 

operate anywhere from 100 to several 

thousand hours per year. Hence, although there are far more emergency 

generators in Massachusetts, prime engines are a larger source of diesel pollution in the state due to their longer hours 

of operation. 

Currently, diesel generators are regulated differently depending on how they 

are used. The result has been confusing 

Table 3: Estimated Diesel Generators 

- in Massachusetts3 1 

Diesel Generators Number in 

by Type of Use Massachusetts 

Emergency Stand-by 2,126 

Generators 

Prime Generators 331 

Portable Generators 3,180 

TOTAL 5,638 

and inconsistent standards for not only 

diesel generators but for all micropower. 

This needs to be improved by developing standards that are based on environmental and public health impacts. 

Emissions 

Diesel generators are a significant source 

of air pollution in the state of Massachusetts and nationwide. 3 2

 As diesel fuel 

burns, over forty identified toxic air contaminants are released into the air we 

breathe. The primary pollutant is nitrogen oxides, which can cause lung function deterioration and other serious 

human health effects. Additional pollutants include carbon monoxide, carbon 

dioxide, sulfur oxides, and volatile organic 

compounds. See Table 5 for a description 

of the health and environmental effects 

of these pollutants. 

Emissions from diesel generators can 

have a large impact on ambient air quality at times of heavy use. This can be a 

Table 4. Estimated NOx Emissions from Diesel Generators 

in Metro Boston During Peak Use3 4 

Estimated 

Number of ; 

Diesel 

Generators 

Estimated 

Capacity of 

Diesel 

Generators 

(MW) 

: NOx " . 

Emission 

:Ra'te|^>:v;;v" 

(Ibs/MWh) 

NOx 

Emissions 

•J (tons/day) 

1,237 408 21.8 2.7 

Micropower at the Crossroads 19 
Table 5: Description of Emissions 

Name of 

Pollutant 

Abbreviation 

Source and Environmental Impacts Health Impacts 

Carbon 

Monoxide 

CO CO is produced by burning organic matter 

such as fossil fuels, wood and charcoal. 

Motor vehicles produce 67% of the manmade CO that is released into the atmosphere. 

Fatigue, angina, reduced 

visual perception and 

dexterity, death in closed 

space. 

Carbon 

Dioxide 

co2 C 0 2 is produced by burning organic matter 

such as fossil fuels, wood and charcoal. C0 2 

is a greenhouse gas. 

Major contributor to global 

warming, which has been 

linked to an increase in the 

spread of disease. 

Nitrogen 

Oxides 

NOx Oxides of nitrogen are the chemicals responsible for giving smog its brown appearance. 

NOx contributes to the formation of ozone, 

production of particulate matter pollution, 

and acid rain. 

Irritates lung tissue, causes 

bronchitis and pneumonia, 

has been linked to a 

decrease in lung function 

growth. 

Particulate 

Matter 

PM Particulate matter consists of soot and dust 

particles that are smaller than the diameter 

of a human hair. Electricity generation, transportation and industry generate roughly 

equivalent proportions of PM. 

Penetrates deep into the 

lungs and is associated with 

numerous respiratory and 

cardiac problems and 

cancer. 

Sulfur 

Oxides 

SOx Oxides of sulfur are produced by the burning 

of fossil fuels. Large emitters of SOx include 

motor vehicles, refineries and power plants. 

SOx contributes significantly to acid rain. 

Reduces respiratory volume, increases breathing 

and nasal airway resistance. 

Volatile 

Organic 

Compounds 

VOC/UHC VOCs are a class of reactive organic gases 

that contribute to the formation of ozone 

and smog. Motor vehicles, refineries and 

power plants are the primary source of VOCs. 

Levels of VOCs are often determined by 

measuring unburned hydrocarbons (U.HC). 

Coughing, fatigue and 

nausea; contributes to the 

inflammation of lung tissue 

and reduced lung capacity. 

Air 

Toxics 

Air toxics like benzene, toluene, and formaldehyde are formed from fossil fuel processing and combustion. The U.S. EPA has 

identified 188 chemicals as hazardous air 

pollutants. 

Cancer, reproductive 

disorders, developmental 

disorders. 

major factor influencing attainment with 

air quality standards. Hot summer days, 

when air problems are at their worst, are 

the most likely time that micropower will 

be in operation to boost an electricity load 

that is heightened by the heavy use of 

airconditioning. In other words, diesel 

generators put out their highest levels of 

pollution exactly when air quality is the 

most sensitive to increases in pollution. 

Since there has not been any requirement for registering most diesel generators or any statewide inventory of diesel 

generators, it is not possible to measure 

this impact with precision. However, 

estimates can give us a good picture of 

how big a problem this is likely to be. 

Assuming the same number of diesel generators per capita in Massachusetts as 

have been counted in California, and 

20 Micropower at the Crossroads 
Figure 3: Potential Cancer Risk from Activities Using Diesel Fueled Engines 

I I 

Idling School Buses 

Emergency Standby Engine 

Truck Stop 

Low Volume Freeway

 _ 

Distribution Center 

Prime 

Engine 

High Volume Freeway 

0 100 200 300 400 500 600 700 800 

Potential Excess Cancers (Chances per million based on 70-year exposure) 

900 

assuming that the average size of these 

generators is 3 30 kW, 3 3 20% of these generators operating for three hours on a day 

of tight electricity supplies in Boston 

would emit 2.7 tons of NOx. (See Table 

4.) This amount of pollution could push 

the city into non-compliance with clean 

air standards. 

Health Impacts 

The extended use of diesel generators can 

result in serious human health implications, especially since most non-agricultural diesel generators are located in 

densely populated urban areas. Where 

large numbers of people are, so too are 

these under-regulated, high-emitting 

engines that spew smog-forming chemicals, fine particles, and known cancercausing agents. 

This can create significant health risks 

for entire neighborhoods. People living 

within 10-20 average city blocks of a diesel generator operating only 100 hours 

per year experience elevated mortality 

risks.35 

Cancer Risk 

In recent years, an increasing number of 

health organizations, as well as the U.S. 

EPA and state environmental agencies, 

have recognized the cancer-causing effects of diesel exhaust exposure.36

 Air pollution control officials now estimate that 

based on a lifetime risk of seventy years 

exposure, diesel exhaust may be responsible 

for over 125,000 cancer cases each year 

nationwide, including 2,900 in Boston.37 

The cancer risk from an emergency 

standby engine is equivalent to that of an 

idling school bus. The cancer risk from 

prime engines (including non-agricultural engines and agricultural engines) is 

more than that of a low-volume freeway 

or that of a facility that has constant diesel truck traffic. Both current diesel backup generators and prime engines 

substantially surpass the acceptable risk 

level of one in a million cancer cases established by the U.S. EPA. 

The California Air Resources Board 

has estimated that a person's lifetime cancer risk increases by 50% if he or she lives 

Micropower at the Crossroads 
Pnoto Dy nrgn Frequency Active Auroral Researcn 

near a single one-megawatt diesel generator that runs for as little as 250 hours 

annually. 3 8 Another California study 

found the cancer risk in five cities to be 

70-140 times higher than commonly accepted levels in the most affected neighborhoods.39 

Non-Cancer Health Risks 

Diesel exhaust is also known to cause numerous non-cancer respiratory problems. 

Diesel is a major source of particulate 

matter (PM), or soot, which can lodge 

deep in the lungs and result in the exacerbation of asthma, respiratory infections, 

increased susceptibility to allergens, 

chronic obstructive lung disease, pneumonia, and heart disease. A recent study 

found that even short-term exposure to 

PM may in -

crease the 

chance of heart 

attacks in atrisk populations.40 

Diesel exhaust also contains, nitrogen 

oxides (NOx). 

NOx in the 

presence of 

sunlight and 

volatile organic 

compounds forms smog. Recently, the 

USC Keck School of Medicine found in 

a long-term study that both NOx and PM 

can permanently reduce the lung function of a child living in Southern California by as much as 10%. Diesel exhaust 

was believed to be a significant contributor. 4 1 

Many other toxic substances are found 

in diesel exhaust. More than 40 components of diesel exhaust are listed as hazardous air pollutants by the U.S. EPA.42 

Other Fossil Fuel 

Internal Combustion 

Engines 

Natural Gas Engines 

Internal combustion engines fueled by 

natural gas are cleaner than diesel generators, but still have high emissions of 

dangerous air pollutants. Natural gas generators have large reductions in NOx and 

SOx compared with diesel generators, 

medium reductions in PM and C02, and 

minimal reductions in CO and VOCs. 

Natural gas engines are offered with 

two tuning settings - rich burning (stoichiometric) or lean burning (in which the 

air/fuel ratio is increased). However, the 

choice is a trade-off of lowering emissions 

of one pollutant while increasing those 

of another. The low emission tuning will 

reduce NOx and hydrocarbon emissions, 

but increase C02 emissions. All other 

Table 6: Emissions of Diesel and Gas Micropower and Large New Power 

Plants (Ibs/MWh) 4 3 

Generator Type Efficiency NOx CO so2 PM10 UHC co2 

Diesel Engine 38% 21.8 6.2 0.5 0.8 1.2 1,432 

Natural Gas Engine 

(lean burn) 

36% 2.2 5.0 0.01 0.03 16.5 1,108 

Natural Gas Engine 

(rich burn) 

29% 0.5 4.0 0.01 0.03 0.4 1,376 

Combined Cycle 

Natural Gas Power Plant 

5 1% 0.06 0.1 0.004 0.04 0.05 776 

22 Micropower at the Crossroads 
emissions are similar between the two 

tunings.4'

1

 Natural gas generators still 

contribute significantly to the same environmental and health impacts described 

in Table 5. 

Engines Using Other Fossil Fuels 

ICEs can also use gasoline, propane, and 

kerosene as fuel. Though not as common 

as diesel and natural gas generators, such 

generators are commercially available. 

Emissions levels from gasoline-fueled 

ICEs fall between those of natural gas and 

diesel-fueled generators. Gasoline generators are the cheapest generators on the 

market, but have a reputation of high 

maintenance requirements as compared 

to generators using any of the other fossil 

fuels. 

Propane generators emit very similar 

amounts of pollutants as the natural gas 

generators.45 

Improving Engines 

for Emergency and 

Portable Use 

Due to the severe public health and environmental hazards associated with ICE 

generators, their use should be limited to 

emergency back-up generation and portable operations, and then only when 

operated in conjunction with emissioncontrol measures. The pollution-reducing 

measures that can reduce the harmful 

impact of diesel generators on nearby 

communities include fuel advancements, 

control technologies, improved efficiency, 

and stringent operations standards. 

• Fuel Advancements - The U.S. EPA 

recently adopted regulations requiring 

petroleum producers to distribute lowsulfur diesel (15 ppm sulfur content) 

nationally by 2006 for vehicle use. 

This rule should also apply to off-road 

diesel use. Massachusetts should 

institute this requirement on its own. 

Because most advanced diesel pollution control devices are sulfursensitive, such steps to require 

low-sulfur diesel are essential to 

achieve further emissions reductions 

for diesel engines. 

• After-Treatment Technology / 

Emission Control - Particulate traps 

physically capture particulate matter 

in a filter and can reduce PM emissions by 83%. 4 6

 Selective catalytic 

reduction (SCR) uses ammonia as a 

catalyst to break down NOx. SCR 

systems have been shown to reduce 

NOx by 65% to 99%.47 Nitrogen 

oxide adsorbers have the potential to 

reduce NOx by 90%. This technology involves both a chemical catalyst 

and burning the filter clean. Even 

with these improvements, however, 

diesel and other fossil fuel generators 

are still dirtier than the good 

micropower technologies discussed 

earlier. 

• Increased Efficiency - The efficiency 

of ICE generators can be improved 

by ensuring proper installation and 

sizing. Improper installation can 

account for a 25% loss in efficiency. 

Another way to improve efficiency is 

to capture and reuse the generator's 

heat. The waste heat produced by 

the generator can be recovered to 

provide energy for further electricity 

production or space and water 

heating. This can reduce emissions 

by 35 to 50%. 

• Hours of Use - Reducing the operating hours of ICE generators will also 

reduce the amount of pollution that 

is released into the air we breathe. 

Key Recommendations for 

Dirty Micropower 

The Massachusetts state government has 

an obligation to protect the state's air 

Micropower at the Crossroads 23 
quality. Since the move to local power 

generation has partly involved an increased reliance on the most polluting 

forms of electricity generation, state 

agencies should take steps to discourage 

the use of dirty micropower. This would 

include the following measure's. 

• Require that all micropower units 

operated in Massachusetts receive 

certification or permits as a condition for being connected to the 

electric grid. 

• Provide incentives for the trade-in 

and upgrade of polluting micropower 

installations. 

• Require that transmission grid 

operators draw on clean, efficient 

micropower before similarly priced 

dirty installations. 

• Require ultra low-sulfur diesel for all 

diesel engines in Massachusetts, on 

and off-road. 

• Establish a clear and limited definition of "emergency use." 

Manufacturers and distributors of diesel generators used the 

"energy crisis" to encourage consumers to purchase polluting 

home power systems. 

24 Micropower at the Crossroads 
NEW MICROPOWER TECHNOLOGIES 

N

ew technologies for generating 

local power are emerging in the 

marketplace. Although they are 

not as clean as the renewable energy 

sources, most of these alternatives are 

distinct improvements over current diesel generators. By phasing in stringent 

standards regardless of technology, state 

officials will push manufacturers to improve these technologies to limit harmful emissions. 

Some of these micropower options can 

be used in combined heat and power 

applications. They are not as simple to 

operate and maintain as sustainable options such as wind and solar, but they are 

often versatile and reliable. Most available technologies utilize carbon-based 

fuels. While they pollute less than diesel 

engines, they still emit harmful gases. 

Alternative Fuel 

Reciprocating Engines 

The reciprocating engine, or internal 

combustion engine, is the traditional engine used in vehicles and diesel generators, as noted above in the "Dirtiest 

Micropower" section. This system draws 

air into a cylinder, compresses the air to 

heat it, then injects fuel, which ignites 

when mixed with the hot air. The resulting explosion moves the piston. It is an 

open system, meaning that it does not 

reuse the air it draws in; instead it releases 

it into the atmosphere as exhaust heat and 

gases. 

Stationary reciprocating engines, like 

the diesel generator, are typically 5 M W 

or less, with the 1-3.5 M W range being 

the largest growing segment recently.48 

When fueled by traditional fossil 

fuels, these engines are the most polluting of the micropower options. When 

operated with alternative fuels, however, 

their emissions can be reduced. See Appendix A for information on alternative 

fuels. 

Turbines 

A gas turbine differs from the reciprocating engine in that it uses a continuous 

combustion process rather than intermittent combustion. Like a reciprocating engine, the basic gas turbine is an open 

system, but it can be modified to reuse 

its exhaust heat. Exhaust treatment technologies can reduce NOx emissions significantly, and some manufacturers are 

now incorporating similar technology 

into the combustion process itself.49 

Gas turbines have traditionally been 

manufactured to generate several hundred megawatts for use as central power 

plants. Now some manufacturers are scaling down their units to less than 30 

MW. 5 0 Most new turbines are fueled by 

natural gas. Some can also use other petroleum fuels or a dual-fuel configuration. 

Microturbines 

Introduced over the last few years, the 

microturbine has a rapidly growing market. Based on the same technology as a 

jet engine, although much reduced in size 

and improved with advanced components 

and software, microturbines can provide 

power in the 25 kW to 500 kW range. 

The initially available commercial units 

generate power ranging from 28 kW to 

75 kW. These smaller units are about the 

size of a refrigerator. 

The turbine shaft of a microturbine 

spins as fast as 100,000 rpm. The highfrequency power generated is then converted to 60Hz for common use. This 

Micropower at the Crossroads 
simple design lends itself well to the lowmaintenance needs of distributed generation. 5 1 

Microturbines have the potential to 

operate on a variety of fuels. Manufacturers, with some support from federal 

and state agencies, are working to improve 

microturbine performance, including generation efficiency. Models built to date 

have lower efficiency, and thus higher 

C02 emissions, than traditional engines. 

In addition to their small physical size 

and flexibility regarding fuel sources, 

microturbines have only one moving part 

and, therefore, low maintenance costs. 

They are highly suitable for combined 

heat and power applications. 

Microturbines' advanced fuel combustion technology results in low NOx emissions, without any emission control 

technology, in comparison with gas-fired 

central station plants. Early tests indicate 

that this emissions performance will be 

maintained over extended operating periods. Capstone Turbine Corporation 

claims that current units emit NOx at the 

rate of 0.50 lbs/MWh, and projects that 

performance improvements will decrease 

NOx emissions to 0.14 lbs/MWh by 2005 

and 0.05 lbs/MWh by 2008. 

Stirling Engines 

Stirling engines are powered by the expansion of a gas that results when the gas 

is heated and the compression of a gas 

that results when the gas is cooled. In this 

closed cycle system, a fixed amount of gas 

is externally heated, usually by combustion, and as it expands and contracts, it 

moves the pistons. 

Theoretically these engines can use any 

heat source. Currently systems are being 

developed that use biomass, woodchips 

and solar heat. Stirling engines are physically smaller than conventional engines 

and relatively quieter. Engines ranging 

from 500 watts to 10 kW are either available now or under development. 

Emissions associated with Stirling engines vary according to the heat source 

used. The Stirling engine itself has no 

emissions, so when it is developed to use 

solar heat as the heat source, the entire 

system will be emission-free. When fossil 

fuels are burned to provide the heat source, 

there are emissions. Since the combustion 

takes place externally, it can be monitored 

to burn fuels completely and limit the temperature, reducing emissions somewhat. 

Potential Advantages of 

Emerging Technologies 

Technical advancements, including improvements in fuel combustion and emissions reduction equipment, have the 

potential to significantly reduce the environmental impacts of these micropower 

technologies. Federal, state and manufacturer-funded research and development 

programs are pursuing such improvements. Clear emissions standards will 

provide clear signals regarding technology performance targets, and a strong 

incentives policy can establish attractive 

market advantages for the cleanest 

micropower technologies. 

Key Recommendations for 

New Micropower 

These technologies already show the 

promise of being safer for public health 

than the dirtiest micropower. But to make 

sure that they move toward the cleanest 

micropower technologies, we must ensure that pollution standards are applied 

across the board to all developing technologies, and complement the standards 

with policies that provide economic and 

other incentives to the cleanest micropower systems. State agencies should take 

the following actions. 

• Establish priority funding for 

clean micropower technology 

advancement. 

26 Micropower at the Crossroads 
Streamline the permitting process for 

clean units that meet or beat air 

pollution standards. 

Require that all micropower units 

operated in Massachusetts receive 

certification or permits as a 

condition for being connected to the 

electric grid. 

• Ensure adequate enforcement of 

emissions standards and establish 

significant penalties for violation. 

Micropower at the Crossroads 
POLICY RECOMMENDATIONS 

M

icropower is here to stay, and 

is likely to expand rapidly in 

the coming years. This is both 

an opportunity and a risk for public health 

in Massachusetts. Clean micropower options have the potential to greatly reduce 

dangerous emissions from electricity production, but the most common micropower technology - the diesel generator 

- is even more polluting than the leading 

technologies ofhrge central power plants. 

Principles 

To ensure that public health is protected 

and that new technologies that reduce 

pollution are encouraged, micro-power 

policy should be based on the following 

principles: 

o Distributed generation must be as 

clean as or cleaner than the cleanest 

central power plant technology 

currently in widespread use. Regulations should target attainment of 

equivalent performance as soon as 

practical. 

o State rules and incentives must 

promote the cleanest energy industry 

for the future of Massachusetts. 

o Regulations should be as simple as 

possible so manufacturers can 

anticipate changes and comply with 

new technology requirements. 

Primary Recommendations 

State agencies can help move micropower in the right direction. To protect 

the health of the people of Massachusetts 

and the air quality of the state while helping to assure reliable local power generation, we recommend the following 

o Set stringent emissions standards for 

all micropower units operated in 

A4assachusetts. 

Micropower at the Crossroads 

o Conduct a comprehensive inventory 

of existing micropower and other 

onsite generation. 

o Streamline the permitting process for 

clean units that meet or beat air 

pollution standards. 

o Ensure adequate enforcement of 

standards and establish significant 

penalties for violation. 

Additional Recommendations 

In addition, many other specific policies 

could ensure that the move to local power 

generation leads to air quality benefits rather 

than a digression to polluting technologies. 

We recommend that state agencies: 

Establish standards and rules for 

micropoiver operation: 

• Require that all micropower units 

operated in Massachusetts receive 

certification or permits as a condition for being connected to the 

electric grid. This policy establishes 

a check against the operation of 

excessively polluting micropower 

systems and preferred treatment 

for the cleanest micropower 

options. 

• Require that transmission grid 

operators draw on clean, efficient 

micropower before similarly priced 

dirty installations. Air pollution emissions should be considered in decisions 

regarding which generators are used 

in times of excess power capacity. 

• Require emissions control measures 

for diesel generators used for emergency back-up power supply. Backup generators will continue to be a 

major pollution problem if they are 

left out of the regulatory picture. 
• Require that all new residential and 

commercial construction be "solarready" with the basic infrastructure 

to ease future installation of photovoltaic panels. 

Provide funding for clean micropower: 

• Require formal consideration of 

clean micropower as a potential least 

cost alternative to transmission and 

distribution upgrades and a means of 

avoiding the cost of future environmental regulation. 

• Establish priority funding for clean 

micropower technology advancement. State research and development programs can target the most 

promising clean micropower technology options. Public money for the 

development of these technologies 

would be a good investment for the 

long-term health of the state economy. 

• Expand the availability of financial 

incentives, including financing 

assistance, buy-down programs, tax 

credits, and grants, for the installation of clean micropower. As long as 

consumers are expected to shoulder 

the burden of the investment costs of 

new technology, the government 

should provide financial assistance. 

• Provide incentives for developers to 

include clean micropower at new 

residential or commercial construction projects. Since builders don't 

pay the ongoing energy costs of the 

units they build, they are reluctant to 

include energy saving measures that 

will increase the initial sale price of 

their buildings. 

• Provide incentives for the trade-in 

and upgrade of polluting micropower 

installations. Other states have 

shown this to be a cost-effective 

approach to reducing air pollution. 

Clear hurdles to the implementation of clean 

micropower: 

• Streamline the permitting and utility 

interconnection process for clean 

micropower installations. Micropower is currently at a disadvantage 

compared with traditional power 

generation due to an unnecessarily 

complicated interconnection process. 

Eliminating this disadvantage for 

clean micropower would promote its 

expansion. 

• Develop incentive tariffs and reduced 

standby and exit fees for clean 

micropower installations. This would 

address financial disincentives in 

utility relationships with micropower 

operators. 

The adoption of these recommendations will promote a vital micropower 

system that reduces the negative public 

health impacts associated with diesel and 

other dirty micropower technologies. 

Micropower at the Crossroads 29 
APPENDIX A: ALTERNATIVE FUELS 

S

everal non-traditional fuels have 

been developed that can replace 

pure fossil fuels in some combustion engines, microturbines, Stirling engines, and fuel cells. While some of these 

fuels may hold promise for reducing 

emissions from electricity generation, 

most of them involve levels of health risk 

similar to those of traditional fuels. 

Biodiesel is a fuel that is made from vegetable oils or animal fats. This is the "bio" 

part, which can be used alone, but is usually mixed with conventional petroleum 

diesel fuel at a ratio of 20-30% "bio" to 

70-80% diesel.52 The fuel operates in a 

conventional combustion engine like a 

diesel generator. Compared to regular 

diesel, biodiesel has reduced emissions of 

CO, SO,, and particulate matter, but has 

increased NO and soluble CO, emissions. 

Propane, also called Liquefied Petroleum Gas (LPG), is formed as a by-product of processing natural gas and refining 

crude oil. Propane usage emits no aromatic compounds, benzene or particulates. Engines that are optimized for 

propane have lower CO, emissions than 

diesel generators. Propane can be used 

as a substitute for diesel fuel in internal 

combustion engines. 

Ethanol is made from the fermentation 

of sugars or starches in grains, agricultural feedstocks and agroforestry products. Ethanol is mixed with gasoline in 

different percentages to be used as a fuel. 

Methanol is predominantly made from 

steam reforming of natural gas. It can also 

be made from feedstocks of coal or biomass, but currently these are not as economical. Like ethanol, methanol is mixed 

with gasoline to be used as a fuel. In these 

gasoline mixtures, both are referred to as 

gasohol and are designed for vehicle use. 

Biomass describes many types of technologies to turn agricultural materials and 

waste into energy. Some are unacceptably 

harmful to the environment while others 

provide a net benefit to the environment. 

The use of biomass in fuel cells, microturbines and Stirling engines is still being researched. 

P Series Fuels are blends of methyltetrahydrofuran (MTHF), ethanol and 

hydrocarbons. Currently MTH F is produced from biomass or petroleum feedstocks. 

30 Micropower at the Crossroads 
APPENDIX B: GLOSSARY 

Back-up generators (BUGs) 

Emergency power generators used to 

avoid potential power interruptions 

caused by malfunctioning power plants, 

natural disasters, or demand overloads on 

the electric grid. 1 3 

British thermal unit (Btu) 

The standard measure of heat energy, 

equal to the amount of energy needed to 

raise the temperature of one pound of 

water by one degree Fahrenheit at sea 

level. It takes about 2,000 Btus to make a 

pot of coffee. 

California Air Resources Board (CARB) 

The regulatory agency that ensures 

California's compliance with the Clean 

Air Act. CARB has done more than any 

other state environmental agency to inventory micropower resources and measure their effects. 

Carbon monoxide (CO) 

An air pollutant produced by burning organic matter such as oil, natural gas, fuel, 

wood and charcoal. Motor vehicles produce 67% of the man-made CO that is 

released into the atmosphere. 

Carbon dioxide (C02) 

A greenhouse gas, produced by burning 

organic matter such as oil, natural gas, 

fuel, wood and charcoal. 

Combined heat and power (CHP) 

A power generation system that uses 

waste heat to heat water, rooms and buildings; provide air conditioning or refrigeration; or provide steam to generate 

more electricity. 

Department of Environmental 

Protection (DEP) 

Massachusetts' regulatory agency that ensures compliance with the Clean Air Act. 

Distributed generation (DG) 

Energy production that occurs near the 

place where it is used. This term is used 

interchangeably with "micropower" 

throughout this report. 

Emergency standby generators 

Often referred to as "back-up generators" or BUGS, these are generators that 

operate on a temporary basis as back-up 

power supplies in the event of power 

outages. 

Fuel cell 

An energy production technology that 

creates electricity and heat through the 

chemical reaction of combining hydrogen and oxygen to make water. 

Kilowatt-hour (kWh) 

The most commonly-used unit of measure telling the amount of electricity consumed over time, equal to one kilowatt 

of electricity supplied for one hour. A 

typical household consumes 500 kWh in 

an average month. 

Megawatt (MW) 

One thousand kilowatts (1,000 kW) or 

one million watts. One megawatt is 

enough energy to power 1,000 average 

Massachusetts homes. 

Megawatt-hour (MWh) 

One thousand kilowatt-hours, or an 

amount of electricity that would supply 

the monthly power needs of a typical 

home having an electric hot water system. 

Microturbine 

A new micropower technology based on 

the same technology as a jet engine although much reduced in size and improved with advanced components and 

software. 

Micropower at the Crossroads 
Net metering 

A system for metering electricity consumption that subtracts the amount of 

power fed back into the grid by a 

micropower unit from the amount that 

is drawn from the grid. 

Nitrogen oxides (NOx) 

The chemicals responsible for giving 

smog its brown appearance. NOx contributes to the formation of ozone, production of particulate matter pollution 

and acid rain. 

Particulate matter (PM) 

An air pollutant made up of soot and dust 

particles that are smaller than the diameter of a human hair. 

Peak load or peak demand 

The electric load that corresponds to a 

maximum level of electric demand in a 

specified time period. Peak periods during the day usually occur in the morning 

hours from 6 to 9 a.m. and during the 

afternoons from 4 to about 8 or 9 p.m. 

The afternoon peak demand periods are 

usually higher, and they are highest during summer months when air-conditioning use is the highest. 

Photovoltaic (PV) panel 

Also known as a solar panel, PVs convert 

sunlight directly into electricity using 

semiconductor technology. 

Prime generators 

Generators used on a regular basis to 

supplement energy from the power grid. 

Portable generators 

Generators that are moved from location 

to location to provide power (motor vehicles and engines used to propel equipment are not considered portable 

generators). 

Sulfur oxide (SOx) 

An air pollutant produced by the burning of fossil fuels. Large emitters of SOx 

include motor vehicles, refineries and 

power plants. SOx contributes significantly to acid rain. 

Volatile organic compounds (VOCs) 

A class of reactive organic gases that contribute to the formation of ozone and smog. 

Motor vehicles, refineries and power plants 

are the primary source of VOCs. 

Wind turbine 

An energy generation technology in 

which the kinetic energy of the wind is 

converted to mechanical power, which in 

turn drives the electrical generator and 

produces an electrical current. 

32 Micropower at the Crossroads 
NOTES 

1. Throughout this report, the terms 

"micropower" and "distributed generation" are 

used synonymously. 

2. Micropower should not be confused with the 

"peaker plants" that are much in the news 

recently. Although both are small electricity 

generating plants, peakers are generators 

operated by utilities and independent power 

producers that are used only during peak 

demand times. They are typically 50-100 MW. 

Micropower units are normally not operated by 

utilities, and are typically in the 2 kW to 1 M W 

range, with some as high as 10 MW. 

3. David Morris, Seeing the Light: Regaining 

Control of Our Electricity System (Minneapolis: 

Institute for Local Self-Reliance, 2001), 54. 

4. Ibid. 

5. Energy Nexus Group, Performance and Cost 

Trajectories of Clean Distributed Generation 

Technologies, 29 May 2002. 

6. Regulatory Assistance Project, Model 

Regulations for the Output of Specified Air 

Emissions from Smaller-Scale Electric Generation Resources: Model Rule and Technical 

Support Documents, November 2001, 

Appendix B. 

7. Ibid. 

8. Ibid. 

9. Many studies have established the links 

between these pollutants and their health effects, 

including D.W Dockery et al, "An Association 

between Air Pollution and Mortality in Six U.S. 

Cities," New England Journal of jMedicine, 

1993. For a good overview of the health effects 

of power plant pollution, see Clean Air Task 

Force, Death, Disease & Dim' Power, October 

2000. 

10. See New York Shines, New York Consumer 

Guide to Buying a Solar Electric System, 

available at www.nyshines.org/pvguide.pdf; 

California Public Interest Research Group, 

Affordable, Reliable Renewables: The Pathway 

to California's Sustainable Energy Future, July 

2001; and California Public Interest Research 

Group, Predictably Unpredictable: Volatility in 

Future Energy Supply and Price from 

California's Over-Dependence on Natural Gas, 

September 2001, available at www.calpirg.org. 

11. U.S. Department of Energy (DOE), Office 

of Utility Technologies, Renewable Energy 

Technology Characterizations, December 1997. 

12. PVhas an average availability factor of 96%: 

Sacramento Municipal Utility District, Sustained Orderly Development of PV, downloaded 

from www.ttcorp.eom/upvg/4.5doc/ 

4.5mwsmd.htm, 4 June 2001. 

13. Solar Boston, Porter Square Shopping 

Center Generates Power from the Sun, downloaded from wM-w.solarboston.org/ 

portersquare.htm, 28 May 2002. 

14. Interstate Renewable Energy Council, SolarPowered Shopping Center Coming to Cambridge, Massachusetts, excerpt from Utility 

Photovoltaic Group Memo, 26 October 2001. 

15. U.S. DOE, Quick Facts about Wind Energy, 

downloaded from www.eren.doe.gov/wind/ 

web.hunl, 15 July 2001. 

16. Danish Wind Turbine Manufacturer's 

Association, Windpower FAQs, downloaded 

from www.windpower.dk/faqs.html, 25 May 

2001. 

17. Lester Brown et al, State of the World 2001 

(NY: W.W. Norton, 2001), 94. 

18. American Wind Energy Association, 

California Electricity Crisis Spurs Sales of 

Home Wind Energy Systems (press release), 13 

February 2001. Wind turbines have an average 

availability factor of 98%: U.S. DOE, Office'of 

Utility Technologies, Renewable Energy 

Technology Characterizations, December 1997. 

19. U.S. EPA, EPA Presents Environmental 

Merit Awards to Eighteen in Massachusetts, 

downloaded from www.epa.gov/region01/pr, 25 

June 2002. 

20. Ibid. 

21. Massachusetts Energy Consumers Alliance, 

Wind Power, downloaded from 

www.massenergy.com/Wind.html, 2 July 2002. 

22. Sunline, Clean Fuels, downloaded from 

www.sunline.org/clean_fuels, 31 August 2001. 

23. FuelCell Energy , PPL Spectrum and 

FuelCell Energy Inc. to Supply Direct Fuel Cell 

Power Plant to United States Coast Guard 

Station (press release), 18 October 2001. 

Micropower at the Crossroads 33 
24. Dave Cleveland, U.S. Coast Guard Cape 

Cod Auxiliary Office, personal communication, 

11 July 2 002.' 

25. Dave Cleveland, personal communication, 7 

August 2002. 

26. U.S. Coast Guard, Fuel Cell Installation at 

Air Station Cape Cod (fact sheet), downloaded 

from www.rdc.uscg.gov, 11 July 2002. 

27. U.S. Combined Heat and Power Association, Combined Heat and Power: Distributed 

Generation Applications that Save Power, 

Reduce Costs, and Improve Energy Security, 

downloaded from www.nemw.org/uschpa/ 

papers.htm, 17 August 2001. 

28. U.S. Department of Energy, Energy 

Secretary Richardson Joins Massachusetts 

Congressional Representatives to Dedicate New 

Cogeneration System at Maiden Mills, 8 

Novemher 1999. 

29. U.S. Combined Heat and Power Association, 2000 EnergyStar Combined Heat and 

Power Awards, 22 June 2001. 

30. Massachusetts DEP, "Stationary Source 

Emission Inventory System" (spreadsheet), 14 

March 2001. 

31. Extrapolation of California data from 

California Air Resources Board (CARB), Diesel 

Risk Reduction Plan, Appendix- II , October 

2000. Number of non-agricultural generators 

translated per capita. Number of agricultural 

generators translated by ratio of gross state 

product of farming sector (DOC, Bureau of 

Economic Data, Regional Accounts Data, 2000). 

32. State numbers are in the previous section. 

An estimated 371,000 tons of NOx and 16.7 

million tons of C02 are emitted from diesel 

generators nationwide: Virinder Singh, Renewable Energy Policy Project, Blending Wind and 

Solar into the Diesel Generator Market, Winter 

2001. 

33. 330 kW average diesel generator size 

estimate from analysis of the 2001 Diesel and 

Turbine Worldwide Annual Power Generation 

Survey by Power Systems Research, 2001. 

34. Number of generators is the per capita 

equivalent of California data for non-agricultural prime and emergency back-up generators 

from CARB, Diesel Risk Reduction Plan, 

Appendix II , October 2000. Estimated capacity 

is based on an average capacity of 330 kW. NOx 

emission rate from Regulator)' Assistance 

Project, Model Regulations for the Output of 

Specified .Air Emissions from Smaller-Scale 

Electric Generation Resources: Model Rule and 

Technical Support Documents, November 2001, 

Appendix B. 

35. Nancy Ryan, Kate Larsen, and Peter Black, 

Environmental Defense, Smaller, Closer, 

Dirtier: Diesel Backup Generators in California, 

August 2002. 

36. Cal EPA, Chemicals Known to the State to 

Cause Cancer or Reproductive Toxicity, revised 

1 May 1997. 

37. State and Territorial Air Pollution Program 

Administrators and the Association of Local Air 

Pollution Control Officials, "Cancer Risk from 

Diesel Particulate: National and Metropolitan 

Area Estimates for the United States," 15 March 

2000. 

38. CARB, Attachment to Letter on Emergency 

Generators: Air Pollution Emissions from 

Electricity Generation, 21 February 2001. Based 

on 70-year exposure. 

39. See note 35. 

40. A. Peters et al, "Increased Particulate Air 

Pollution and the Triggering of Myocardial 

Infarction," Circulation 103 (23), 12 June 2001. 

At-risk populations are considered to be 

children, athletes, people with respiratory 

disease, and the elderly. 

41. W.James Gaudennan et al, Association 

between Air Pollution and Lung Function 

Growth in Southern California Children, 2 May 

2000. 

42. CARB and Office of Environmental Health 

Hazard Assessment, Proposed Identification of 

Diesel Exhaust as a Toxic Air Contaminant, 22 

April 1998. 

43. See note 6. Micropower figures represent 

emissions from units with no emissions treatment, which is typical of most current 

micropower facilities. 

44. Nathanael Greene and Roel 

Hammerschlang, "Small and Clean Is Beautiful: 

Exploring the Emissions of Distributed Generation and Pollution Prevention Policies," 

Electricity Journal, 2000. 

45. Mark Delucchi, Propane Education and 

Research Council, LPG for Forklifts: A 

Fuelcycle Analysis of Emissions of Urban Air 

Pollutants and Greenhouse Gases (press release), 

17 September 1999. 

46. CARB, Diesel Risk Reduction Plan, 

34 Micropower at the Crossroads 
r . 

Appendix II, October 2000. 

47. Union of Concerned Scientists, Rolling 

Smokestacks: Cleaning Up America's Trucks and 

Buses, October 2000. 

48. Seth Dunn, Worldwatch Institute, Micropower: The Next Electrical Era, July 2000. 

49. See note 5. 

50. See note 48. 

51. See note 5. 

52. National Biodiesel Board, Biodiesel 

Frequently Asked Questions, downloaded from 

www.biodiesel.org/general/faq.htm, 22 August 

2001. 

53. Thanks to the California Energy 

Commission (www.energy.ca.gov/glossary) for 

many of these definitions. 

Micropower at the Crossroads 35