Environmental Health & Engineering, Inc

. 117 Fourth Avenue Needham, MA 02494

- 2725
TEL 800

- 82 5

- 5343 781

- 247

- 4300 FAX 781

- 247

- 4305
www.eheinc.com

Memorandum on Acid Gases 2011

- 03

- 02 Page 1 of 10 TO: Janice E. Nolen

Assistant Vice President, National Policy and Advocacy American Lung Association

FROM: David L. MacIntosh, Sc

. D

. , C

. I

. H

.
DATE: March 2 , 2011

RE: Acid Gas Emissions and Coal

- Fired Power Plants

This memorandum addresses acid gas h azardous a ir p ollutants (HAPs) emitted by coal

- fired
electric u tility b oilers in relation to the Maximum Available Control Technology (U tility MACT )
rules scheduled to be proposed by the U.S. Environmental Protection Agency (USEPA) by March 16, 2011. The a cid gases h ydrogen c hloride (HCl) and h ydrogen f luoride (HF) are
considered ; including their intrinsic hazards
, emissions , impacts on the environmen t, control of emissions, and collateral benefits of their control. The Clean Air Act Amendments of 1990
iden tified more than 180 HAPs, including HCl and HF, which are known or suspected to cause adverse consequences to human health and the environment , making them subject to regulation under Se ction 112 of the Clean Air Act.

Acid Gases Hydrogen chloride and hyd rogen fluoride are strongly corrosive gases produce d by coal

- burning power plants. When combined with water, hydrogen chloride gas forms hydrochloric acid. T he Agency for Toxic Substances and Disease Registry (ATSDR) characterizes hydrochloric acid as

― cor rosive and can cause irritation and burns‖ at high concentrations ( ATSDR, 2010a) . Similarly, for high exposures to HF, the Agency states that ― h ydrogen fluoride is irritating to the skin, eyes, and mucous membranes, and inhalation may cause respi ratory irr itation or hemorrhage ‖ (ATSDR, 2010b). These effects occur at l evels of exposure likely above what are generally
encountered in outdoor air.

According to the USEPA National Emissions Inventory, 335,000 tons of hydrogen chloride and 45,000 tons of hydrogen fluoride are likely released each yea r by coal

- burning power plants.Memorandum on Acid Gases 2011

- 03

- 02 Page 2 of 10

The amounts of hydrogen chloride and hydrogen fluoride produced by a particular power plant depend in large part on the concentrations of chloride and fluoride in the coal that is burned and whether any emission control systems are in use. Overall however, approximately 60% of the
chloride and fluoride in coal burned in power plants is estimated to be released to the atmosphere as hydrogen chloride and hydrogen fluoride (USEPA, 1998a).

C oal

- burning power plants are reported to be the largest anthropogenic source of hydrogen chloride and hydrogen fluoride emissions to air ( US EPA, 2009 a ). Due to its high solubility in water, the majority of HCl is believed to be rapidly removed from the atm osphere by wet and dry deposition as well as by reactions with particles in the atmosphere (Sanhueza, 2001). Hydrogen fluoride is emitted as a gas or particle and can be adsorbed onto other particles (USE P A, 1998b). Hydrogen fluoride containing particles t end to remain suspended in the atmosphere longer than hydrogen chloride gas and can travel up to 500 kilometers or more as fine particles (USE P A, 1998b).

Because of their high solubility in water, acid gas vapors can readily react with the moisture/tissu es in the upper airways. Likewise , water bound to microscopic particles can act as a ―delivery system‖ for acids to the alveolar regions of the lung (USEPA, 1998b). Controlled exposures of people with asthma have shown irritation and restriction of the air ways from exposure to hydrogen chloride (Fine, 1987). Other studies have shown both acids to irritate eyes, nasal passages and the lungs (USEPA, 2000a; USEPA, 2000b)

.

While the US EPA estimated that hydrogen chloride levels resulting from coal

- fired power plant emissions are below published health

- based guidance levels (USEPA, 1998a), the Agency states that it has ―low confidence‖ in the guidance level (called a ―reference concentration‖) due to limited study of this compound in human populations (USEPA 200 0a ) . W hen combined with water, 100% of the hydrogen chloride dissociates and form s hydrochloric acid. For our purposes think of this complete dissociation as a characteristic of a ―strong acid‖. Other ‖s trong acid s‖ in the atmosphere can result from emiss ions of nitrogen

- based and sulfur

- based gases
releas ed from coal

- fired power plants (producing nitric acid and sulfuric acid, respectively)

. S trong acid s or their precursors that are present in inhaled particles and gases have been linked with respiratory effects in large

- scale epidemiological studies. A study of 13,000 children in 24 U.S. and Canadian cities found that strong acidity in particles was associated with increased episodes of bronchitis and reduced lung function and acid gases were associated w ith asthmaMemorandum on Acid Gases 2011

- 03

- 02 Page 3 of 10

and related symptoms in children (Raizenne, 1996; Dockery, 1996). A more recent major children’s study found also acid gases and particle pollution were associated with reduced lung function (Gauderman et al., 2004). The focus of th ese landmark stud ies on children is significant ; as children are likely more vulnerable than a healthy adult to air pollution, including acidic gases and particles. Children have narrower airways, a faster breathing rate and tend to spend more time outdoors than adults , resulting in greater overall exposures ( ATSDR , 2011 ; AAP, 2004 ). Results from th ese stud ies and other research (USEPA 1998a) show the potential harm from HCl vapor, particularly in the vicinity of coal burning power plants , where its
contribution to acid aerosols and acid ic precipitation has been not well

- characterized

.

Chloride released from hydrogen chloride can also significantly increase cloud acidity (USEPA, 1998b) and contribute to acid deposition over a regional scale. While much of the strong a cidity has generally been thought to be related to sulfur dioxide and nitrogen oxide emissions, hydrogen chloride in particular likely plays a significant role in acid deposition in the vicinity of
coal

- burning power plants. Particularly within 15 k ilo m ete rs of a power plant, US EPA has suggested that "...acidity in rainwater near a coal

- fired power plant may be predominately the result of hydrogen chloride rather than sulfur dioxide or nitrogen oxides."

Acid gas emissions from power plants can also adversely impact ecosystems. A recent study in the United Kingdom attributed almost a third of the improvements from acid rain contamination since 1986 to reductions in hydrogen chloride from coal burning power plants (Evans, 2011). This is a much larger fraction t han previously estimated. This study also showed that hydrogen chloride likely travels much further in the atmosphere than previously thought . Finally, this paper
concludes: ―Remarkably, [hydrogen chloride] has largely been overlooked in scientific

assessm ents of ec osystem air pollution impacts.‖

Acid Gas Controls
B ased on data gathered by the US EPA
, c ontrol technologies for acid gases currently exist, are already in use by some power plants, and are effective at controlling acid gas emissions

. (USEPA, 200 9 b; USEPA, 2009c ). As shown in the chart below, hydrogen chloride and hydrogen fluoride emissions for a sample of better controlled coal

- fired power plants were five times lower than emissions from a randomly selected set of coal

- fired power plants.Memorandum on Acid Gases 2011

- 03

- 02 Page 4 of 10

Coa l, especially some b ituminous coal s can have significant chlorine content, which contributes to hydrogen chloride emissions when this type of coal is burned (Staudt 2010) . Electric utility boilers that fire bituminous coal comprise roughly half of the coal

- fired electric generating capacity of the U.S. Although many of these facilities are equipped with wet scrubbers that are highly efficient at capturing hydrogen chloride and other acid gases ( e.g. , hydrofluoric acid), a large number of bituminous fueled u nits are not equipped with scrubbers

— having only particulate controls
, and could require acid gas controls to meet emission limits set under the
U tility MACT rules.

In order to meet the MACT standards for hydrogen chloride and hydrogen fluoride, some of t he uncontrolled facilities may choose to install wet or dry scrubbers , also known as flue gas
desulfurization

. Wet scrubbers are more efficient at removing acid gases, but they are more costly than dry scrubbers. Modern wet scrubbers typically reduce sulfu r dioxide emissions by
about 98 % 1 ; have higher capture rates for hydrogen chloride ; and reduce emissions of sulfur

1 2009 EIA Form 860Memorandum on Acid Gases 2011

- 03

- 02 Page 5 of 10

trioxide and sulfate as well by about 50% or more. Reduction of sulfur trioxide and sulfate by wet scrubbers is supported by data in US EPA’s Information Collection Request (USEPA 2009a; USEPA 2009b) on bituminous coal units equipped with an electrostatic precipitator (ESP)

. A review of these data showed significant reductions in condensable particulate emissions when comparing the average emis sion s of units with wet flue gas desul f urization versus those without it, as shown in T able 1

. Condensable particulate matter consists of substances, such as many metals, that are a vapor in the hottest portions of an exhaust stack, but rapidly condense to form primary particulate matter (PM)

. These values are the results of relatively small data sets and may not be representative for all facilities, but they show a large reduction in condensable PM from the use of this technology.

Table 1 Comparison of A verage Emission Rate of Condensable PM from IC R Data for

Bituminous Coal Facilities With and Without Wet Flue Gas Desulfurization or ―Scrubbers‖

Emission Rate, pounds per million British Thermal Units

PM Control Device Without Scrubbers With

Scrubber s Percent

Reduction Electrostatic Precipitators 0.041* 0.009 78%
*This data included units with selective catalytic reduction, which would increase condensable PM somewhat, but t ypically not more than doubling it.

Because of the cost of wet scrubber s (and to a lesser extent, dry scrubbers) , other technologies are likely to be deployed for hydrogen chloride capture from unscrubbed bituminous coal fired boilers. Many unscrubbed facilities may install dry sorbent injection, which is much less expensive to install than a wet scrubber. Dry sorbent injection offers the ability to reduce both hydrogen chloride and sulfur oxides
, but is generally less effective at removal of sulfur dioxide than the more costly wet or dry scrubbers.

At one facility hydrogen chloride and sulfur dioxide were removed using dry sorbent injection with both a baghouse (or fabric filter) and an ESP for particle collection (Davidson, 2010) . This study showed that the unit with an ESP , the most commonly used PM control device on power plants, remov ed 95% of the hydrogen chloride and 50% of the sulfur dioxide. At the Mirant
Potomac Ri ver Power Plant, equipped with dry sorbent injection and an ESP , roughly 98% ofMemorandum on Acid Gases 2011

- 03

- 02 Page 6 of 10

hydrogen chloride and greater than 70% of sulfur dioxide were captured (Kon g, 2008). A review of power plant data showed significant reductions in condensable PM emissions when comparing the average emissions of units with dry sorbent injection versus those without, as
shown in Table 2 (USEPA 2009b; USEPA, 2009c ). These values ar e the results of relatively small data sets and may not be representative for all facilities, but they show large reductions in condensable PM from the use of this technology.

Table 2 Comparison of Average Emission Rate of Condensable PM from ICR Data fo r

Facilities With and Without Dry Sorbent Injection (DSI)

Emission Rate, pounds per million British Thermal Units

PM Control Device Without DSI With DSI Percent Reduction Electrostatic Precipitators** 0.041* 0.007 83% Fabric Filters*** 0.028* 0.003 91%
* This data included units with SCR, that would increase condensable PM somewhat, but typically not more than doubling it. ** Bituminous coal *** Powder River Basin coal

Regardless of which control technology (scrubber s or dry sorbent injection) is selected, the anticipated MACT emission standards are expected to reduce aggregate emissions of HCl and
HF from coal

- fired power plants. Because of the physical and chemical properties of the available control technologies the measures taken to reduce H AP acid gases are also anticipated to lower emissions of condensable PM and sulfur dioxide. These collateral benefits are important because condensable PM and secondary PM formed from sulfur dioxide comprise the majority of fine particulate matter in most areas of the United States.

As described in the most recent comprehensive synthes e s of the science, both short

- ter m and long

- term exposure to fine particulate matter has been found to cause cardiovascular effects
, including mortality (USEPA 2009d; CASAC 2010). In addition, f ine particle exposure has been found to be a likely cause of adverse r espiratory effects, including increased visits to emergency departments and hospital admissions ; worsening o f r espiratory symptoms; and reduced lung
function ( US EPA 2009 d , CASAC 2010 )

. Long

- term exposure to fine particles ha s also been linked to reproductive and developmental effects
, cancer, mutagenicity and genotoxicityMemorandum on Acid Gases 2011

- 03

- 02 Page 7 of 10

( US EPA 2009 d )

. F ine particulate matter h as negative impacts on the environment as well. For instance, sulfate

- laden fine particulate matter is the key contributor to impairment of visibility in pristine areas such as National Parks ( US EPA 2009 d )

. For these reasons, public health and
environmenta l benefits accrued from acid gas controls are expected to be substantial.

The potential value of co llateral benefits from the Utility MACT Rule is indicated EPA’s recent Regulatory Impact Analysis for MACT on industrial boilers ( US EPA 2011 a ). In that ana lysis, EPA estimated that public health benefits of at least $22 billion to $54 billion would be achieved by MACT controls on industrial boilers . In comparison, the costs of controls were estimated to be $1.4 billion. EPA attributed over 90% of the public health benefit to reductions in sulfur dioxide emissions, presumably achieved as a by

- product of acid gas controls on those boilers.
With a benefit

- cost ratio of at least 16 to 1, the public health and economic value of controlling acid gas emissions from those boilers is clear. Although not quantified directly, t echnologies that control acid gas emissions may also reduce emissions of hazardous metals 2 like mercury and selenium, which are not as effectively controlled by conventional particle technologies. ( US EPA, 2010).

While there has been some debate over whether collateral benefits can be considered in rulemaking for HAPs, EPA is expressly authorized by Congress to consider the collateral benefits of controlling sulfur dioxide and other criteria pollut ants when establishing National Emission Standards for Hazardous Air Pollutants (Federal Register, 2010). This interpretation of
the law was recently affirmed . A fter consideration of extensive public comments on this subject
EPA concluded it knows of ―no p rinciple in law or common sense‖ that precludes the Agency from considering collateral environmental benefits when acting to regulate HAP e missions under the Clean Air Act ( US EPA 2011 b )

.

2 As in some EPA materials, the class of pollutants referred to for simplicity here as ‘metals’ includes some elements (e.g. arsenic and s elenium) that are not, strictly speaking, fully metallic.Memorandum on Acid Gases 2011

- 03

- 02 Page 8 of 10

References

Agency for Toxic S ubstances and Disease Registry ( ATSDR ). 2010a. Medical Management Guidelines for Hydrogen Chloride (HCl) . Updated September 1, 2010. Accessed February 27, 2011. http://ww w.atsdr.cdc.gov/MHMI/mmg173.pdf.

Agency for Toxic Substances and Disease Registry (ATSDR ). 2010b

. Medical Management Guideli nes for Hydrogen Fluoride (HF) . Updated September 1, 2010. Accessed February 27, 2011. http://www.atsdr.cdc.gov/mhmi/mmg11.pdf

. Agency for Toxic Substances and Disease Registry (ATSDR). 2011. Toxic Substances Portal: Toxicological Profiles

. Washington, DC, USA: ATSDR. Web Link: http://www.atsdr.cdc.gov/toxprofiles/index.asp [Accessed: 18 February 2011].

American Academy of Pediatrics (AAP) , Committee on Environmental Health. 2004. Ambient Air Pollution: Health Hazards to Children. Pediatrics 114(6):1699

- 1707.

CASAC (2010). CASAC Review of Policy Assessment for the Review of the PM NAAQS

– Second External Review Draft (June 2010), Clean Air Scientific Advisory Committee (CASAC) Particulate Matter (PM) Review Panel.

Davidson, H. 2010. Dry Sorbent Injection for Multi

- pollutant Control Case Study presented at CIBO Industrial Emissions Control Technology VIII Conference

. Portland, ME, USA. Augu st 2

- 5, 2010

. Dockery DW, Cunningham J, Damokosh AI, Neas LM, Spengler JD, Koutrakis P, Ware JH, Raizenne M, Speizer FE. 1996. Health Effects of Acid Aerosols on North American Children: Respiratory Symptoms. Environmental Health Perspectives 104(5):500

- 5 04.

Evans CD, Monteith DT, Fowler D, Cape JN, Brayshaw S. 2011. Hydrochloric Acid: An Overlooked Driver o f Environmental Change. Environmental Science & Technology ( In Press, DOI: d x.doi.org/10.1021/es103574u).

Federal Register . 2010. National Emission S tandards for Hazardous Air Pollutants for Major Sources: Industrial, Commercial, and Institutional Boilers and Process Heaters, Proposed Rule

. 75 (4 June 2010): 32032

. Fine JM, Gordon T, Thompson JE, Sheppard D. 1987. The role of titratable acidity in acid aerosol

- induced bronchoconstriction. American Review of Respiratory Disease 135(4):826

- 830.

Gauderman WJ, Avol E, Gilliland F, Vora H, Thomas D, Berhane K, McConnell R, Kuenzli N, Lurmann F, Rappaport E, Margolis H, Bates D. 2004. The effect of air pollu tion on lung function development in children aged 10 to 18 years. New England Journal of Medicine

. 351:1057

- 1067.Memorandum on Acid Gases 2011

- 03

- 02 Page 9 of 10

Kong Y, de La Hoz JM, Wood M, Atwell M, Lindsay T. 2008. Dry Sorbent Injection of Sodium Bicarbonate for SO 2 Mitigation presented at Internat ional POWER

- GEN 2008 . Orlando, FL, USA. December 2

- 4, 2008.

Raizenne M, Neas LM, Damokosh AI, Dockery DW, Spengler JD, Koutrakis P, Ware JH, Speizer FE. 1996. Health Effects of Acid Aerosols on North America n Children: Pulmonary Function. Environmental He alth Perspectives 104 (5):506

- 514.

Sanhueza E. 2001. Hydroch loric acid from chlorocarbons: A significant global source of background rain acidity

. Tellus Series B Chemical and Physical Meteorology 53(2):122

- 132.

Staudt, J.E., ―Surviving the Power Sector Environmental Regulations‖, Bipartisan Policy Center Workshop on Environmental Regulation and Electric System Reliability, October 22, 2010, available at www.andovertechnology.com

U.S. Environmental Protection Agency (US EPA ). 2011 a

. Regulatory Impact An alysis: National Emissions Standards for Hazardous Air Pollutants: Industrial, Commercial, and Institutional Boilers and Process Heaters, Office of Air Quality Planning and Standards, Research Triangle Park, NC.

U.S. Environmental Protection Agency (US EP A ). 2011 b . National Emissions Standards for Hazardous Air Pollutants: Industrial, Commercial, and Institutional Boilers and Process Heaters, EPA

- HQ

- OAR

- 2002

- 0058.

U.S. Environmental Protection Agency (USEPA). 2010. Air Toxics Standards for Utilities: U tility MACT ICR Data. Part I & II: Final draft (version 2) of selected EU MACT ICR response data (excludes facility contact information), including; All Part I (General Facility Information); and All Part II (Fuel Analysis and Emission Data); including all Hg CEMs data . Web Link: http://www.epa.gov/ttn/atw/utility/utilitypg.html [Accessed 11 January 2011]. U.S. Environmental Protection Agency (USEPA). 2009a. 2002 National

- Scale Air Toxics Ass essment . Web Link: http://www.epa.gov/ttn/atw/nata2002/ [Accessed February 18, 2011].

U.S. Environmental Protection Agency (USEPA). 2009b. Supporting Statement for OMB Review of EPA ICR No. 2362.01 (OMB C ontrol Number 2060

- 0631): Information Collection Effort for New and Existing Coal

- and Oil

- Fired Electric Utility Steam Generating Units, Part A, Final

. Research Triangle Park, NC, USA: USEPA.

U.S. Environmental Protection Agency (USEPA). 2009c. Supportin g Statement for OMB Review of EPA ICR No. 2362.01 (OMB Control Number 2060

- 0631): Information Collection Effort for New and Existing Coal

- and Oil

- Fired Electric Utility Steam Generating Units, Part B , Final

. Research Triangle Park, NC, USA: USEPA.Memorandum on Acid Gases 2011

- 03

- 02 Page 10 of 10

U.S. E nvironmental Protection Agency (USEPA). 2009d. Integrated Science Assessment for Particulate Matter, Includes Errata Sheet created on 2/10/2010 (EPA/600/R

- 08/139F) . Research Triangle Park, NC, USA: USEPA, Office of Air Quality Planning and Standards.

U.S. Environmental Protection Agency (USEPA). 2000a. Air Toxics Web Site: Hydrochloric Acid (Hydrogen Chloride) Hazards Summary . Web Link: http://www.epa.gov/ttn/atw/hlthef/hydrochl.html [Accesse d February 18, 2011].

U.S. Environmental Protection Agency (USEPA). 2000b. Air Toxics Web Site: Hydrogen Fluoride Hazards Summary . Web Link: http://www.epa.gov/ttn/atw/hlthef/hydrogen.html [Acc essed February 18, 2011].

U.S. Environmental Protection Agency (USEPA). 1998a. Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units

– Final Report to Congress, Volume 1 (EPA

- 453/R

- 98

- 004a) . Research Triangle Park, NC, US A: USEPA, Office of Air Quality Planning and Standards.

U.S. Environmental Protection Agency (USEPA). 1998b. Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units

– Final Report to Congress, Volume 2. Appendices (EPA

- 453/ R

- 98

- 004b) . Research Triangle Park, NC, USA: USEPA, Office of Air Quality Planning and Standards.