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NATIONAL COUNCIL FOR AIR AND STREAM IMPROVEMENT, IN C. P.O. Box 13318, Research Triangle Park, NC 27709-33 18 Phone (919) 941-6400 || Fax (919) 941-6401

Vipin K. Varma, PhD Vice President – Air Quality vvarma@ncasi.org

January 8, 2013

Mr. Michael S. Hannan Office of Atmospheric Programs, Climate Change Divi sion US Environmental Protection Agency

1310 L Street NW Washington, DC 20005

Dear Mr. Hannan,

This is in response to your email dated December 20 , 2012 to Ms. Nancy Clark of AFPA, requesting written authorization from NCASI to upload Technica l Bulletin No. 998, Methane and Nitrous Oxide Emissions from Biomass-Fired Boilers and Recovery F urnaces in the GHGRP docket. By way of this letter, NCASI grants EPA written permission to uplo ad the above-mentioned Technical Bulletin to the docket, in connection with the petition for reconsi deration of the CH 4 and N 2 O emission factors in the

GHGRR.

Additionally, you requested clarification on (a) th e statement in page 27 of the Technical Bulletin discussing improper sampling techniques for Nitrous Oxide (N 2 O) and (b) how this relates to the Fortum 2011 report referenced in the Technical Bulletin. Our responses are provided below;

• As discussed in p.27 of the Technical Bulletin, unc onditioned grab samples, collected from combustion sources and stored prior to analysis, ca n generate N 2 O and yield positively biased emission numbers. Muzio et al studied this phenome non and reported that combustion gases containing sulfur dioxide (SO 2 ), nitric oxides (NO

x ), and moisture can form several hundred parts per million (ppm) of N 2 O in the sampling container, even within short dura tions of storage of up to 2 hours (Muzio 1989, referenced in the Tec hnical Bulletin).

• Muzio et.al reported that the mechanism for this ar tifact N 2 O formation involved gas-phase

oxidation of NO to NO 2 , followed by liquid phase conversion of NO 2 and SO 2 to N 2 O and sulfuric acid (H 2 SO 4 ). The mechanisms also indicate that a lower pH wo uld favor the liquid phase reactions. The removal of moisture and SO 2 from the gas stream, and storage at a higher aqueous-phase pH are viable options for conditionin g these grab samples. EPA’s Air and Energy Research Laboratory (AEERL) subsequently dev eloped a sampling protocol for collecting grab samples for the measurement of N 2 O in combustion sources in 1993. The sampling methodology included the use of reactant-s pecific SO 2 and H 2 O sorbents followed by sample collection in a stainless steel container.- 2 -

• The Fortum study (Fortum 2001) acknowledged the pot ential for positive bias due to inappropriate grab sampling, cited the above study by Muzio et al, and reiterated that many of the primary N 2 O measurement data available at that time could be regarded as inaccurate due to

this artifact formation. Our reference to the Fortum study in connection wit h the statement in p.27 is primarily intended to communicate this tech nical group’s acknowledgement of the inadequacy as it relates to existing data.

• The Fortum study utilized a modified sampling / con tinuous measurement technique for obtaining N 2 O emission data. Moisture from the flue gas was re moved using a cooler and the gases were immediately analyzed using an infrared a nalyzer using the Non-Dispersive Infrared (NDIR) technique. Measurements made using the NDIR analyzer also compared favorably with those made using a Fourier Transform Infrared (FTIR ) analyzer at one of the sources tested during the study. It is NCASI’s assessment that this technique of coo ling the sample gas (to remove entrained moisture) followed by immediate an alysis (no sample storage) minimizes the potential for interferences or positive biases due to spontaneous N 2 O formation.

• As discussed in section 2.0 and Appendix C of Techn ical Bulletin 998, NCASI developed a sample conditioning system (drop-out impinger + sil ica gel impinger) to remove entrained

moisture and SO 2 from the flue gas in conjunction with this study to develop emission factors

for CH 4 and N 2 O. The removal of both moisture and SO 2 allows for grab sample storage, especially in cases where instantaneous continuous measurement was not feasible. As discussed in Appendix C, samples collected using the above co nditioning techniques were stable up to 72 hours in storage.

Note on Emission Factors Related to Wood Combustion Reported in the Fortum Study

On the subject of the applicability of emission fac tors developed during the Fortum study, the following points are worth reiterating;

• N 2 O emissions from Fluidized Bed (FB) Boilers – Six out of 13 boilers tested during the Fortum study were FB boilers (3 circulating fluidized bed (CFB) and 3 bubbling fluidized bed (BFB)). This study focused more on fluidized bed boilers gi ven the expectation that the prevalent lower combustion zone temperatures (800oC - 900o C) would result in higher levels of N 2 O emissions.

As discussed in section 5.2 of Technical Bulletin 9 98, combustion zone temperatures in industrial boilers are expected to be significantly higher than 950oC, the presumptive threshold

above which N 2 O formation is expected to be negligible. As expec ted, N 2 O emissions measured during the Fortum study from pulverized coal boiler s were significantly lower than the emissions from CFBs. Additionally, only two of the boilers ( one CFB and one BFB) tested during the Fortum study burned predominantly wood/bark during the tests. Lastly, fluidized bed boilers account for <5% of all forest products industry boi lers that burn biomass fuels. It is therefore inappropriate to use the N 2 O emission factors for fluidized bed boilers, devel oped during the Fortum study, for the broader category of industria l boilers burning biomass fuels. The N 2 O emission data provided in Technical Bulletin 998 ar e more comprehensive and reflect periods with predominantly wood/bark firing.

• CH

4 and N

2 O emissions from Recovery Furnaces – CH 4 emissions from the recovery boilers tested in the Fortum study were either at or below the confidence limit of 1 kg/TJ (<0.001 kg/MMBtu). This is comparable to the average CH 4 emission factors reported in the NCASI- 3 -

study (Table 5.2 in Technical Bulletin 998). N 2 O emissions from recovery furnaces in the Fortum study were also below the confidence limit o f 1 kg/TJ (<0.001 kg/MMBtu). The average

N 2 O emission factor reported in the NCASI study (0.00 044 kg/MMBtu in Table 5.3) is consistent with the conclusion of the Fortum study.

Please do not hesitate to contact me at 352- 331-17 45 (ext. 260) or vvarma@ncasi.org , if you have additional questions on this topic or on the NCASI Technical Bulletin.

Sincerely,

Vipin K. Varma

cc:

Derek Sain, Senior Research Associate, NCASI Brad Upton, Principal Research Engineer, NCASI Reid Miner, Vice President, Sustainable Manufacturi ng, NCASI Nancy Clark, Director, Climate and Air, AFPA