UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WA SHINGTON, D.C. 20460 OFFICE OF AIR AND RADIATION

MEMO RANDUM TO: Docket EPA
- HQ - OAR - 2009 - 0472 FROM: Jason Samenow

Climate Change Division, Office of Atmospheric Programs SUBJECT: Documentation for Computing Changes in oceanic pH resulting from EPA’s

Li ght Dut y Vehicle Greenhouse Gas Emission Standard s Background To calculate the changes in oceanic pH resulting arising from the change in the atmospheric concentration of carbon dioxide ( CO2) resulting from EPA’s Li ght
- Dut y Vehicle Greenhouse Gas Emission Standards , EPA’s Office of Atmospheric Programs used the Program Developed for CO 2 System Calculations (CO2SYS). The program was developed b y Ernie Lewis at Brookhaven National Laboratory and Doug Wallace at the Insitut fuer Meereskunde in Germany, supported by

the U.S. Department of Energy , Office o f Biological and Environmental Research, under Contract No. DE
- ACO2 - 76CH00016. The program is written and compiled using Microsoft QuickBASIC and runs under DOS on almost any

personal computer processor. It can also be run from a Microsoft Excel spreadsh eet or in MATLAB. Itis downloadable in these various formats at Oak Ridge National Laboratory ’s (ORNL) Center for Carbon Dioxide Information and Analy sis Center (CDIAC) Web site: http://cdiac.ornl .gov/oceans/co2rprt.html . This CDIAC Web site also contains full model documentation and references. The program CO2SYS performs calculations relating parameters of the carbon dioxide (CO 2 ) sy stem in seawater and freshwater. The program uses two of the four measurable parameters of the CO 2 system [total alkalinity (TA), total inorganic CO 2 (TC), pH, and either fugacity (fCO 2 ) or partial pressure of CO 2 (pCO 2 )] to calculate the other two parameters at a set of input conditions (temperature and pressure) and a set of output conditions chosen by the user. Methodology and Results Summary We ran the DOS version (Lewis and Wallace, 1998) of the program to compute pH under two emissions scenarios as follows:1) A reference scenario 1 (i.e. , business
- as - usual, no action) in which atmospheric CO 2

concentrations (a lso known as partial pressure) in 2100 reached 788.9 parts per million (ppm) [this scenario assumes a mid
- range climate sensitivity of 3 ° C] in 2100. 2) An emissions reduction scenario 2 in which this rulemaki ng is implemented, reducing atmospheric CO 2 concentrations by 2.9 ppm to 786 ppm [this scenario assumes a mid
range climate sensitivity

of 3 ° C] in 2100. In order to determine the change in pH resulting from the emissions reduction, we subtracted the ref erence scenario pH from the emission reduction scenario pH. We found that emissions reductions result in a 0.0014 increase in pH. The values for pH under the two scenarios varied according to the inputs used. For one set of seawater parameters (described below), the reference scenario (788.9 ppm) pH was 7.7716 and the emissions reduction scenario (786 ppm) was 7.7730. Details Running the CO2SYS program required the input of a number of variables and constants when we ran each scenario (i.e. , both the re ference and emissions reduction). Our choices for these inputs are described below. Upon starting the program, the user is asked for a number of inputs. The inputs we selected were as follows, with our justification for these inputs provided in brackets : 1) Input mode: Single
- input [This means that the program calculates pH for one set of input variables at a time, instead of a batch of variables. It does not affect results]. 2) Choice of constants: Mehrbach et al. (1973), refit by Dickson and Millero (1987) [Further discussion of this input is provided below] 3) Choice of fCO 2 or pCO 2 : pCO 2 [pCO 2 is the partial pressure of CO2 and can be converted to fugacity (fCO2) if desired] 4) Choice of KSO4: Dickson (1990) [L ewis and Wallace (1998) recommend using the equat ion of Dickson (1990) for this dissociation constant. The model also allows the use of the equation of Khoo et al. (1977). Switching this parameter to Khoo et al. (1977) instead of Dickson (1990) had no effect on the difference in pH between the reference and emissions scenario]. 5) Choice of pH scale: Total scale [The model allows pH outputs to be provided on the total scale, the seawater scale, the free scale, and the National Bureau of Standards (NBS) scale. The various pH scales can be interrelated using equations provided by L ewis and Wallace (1998)].

1 For more information on the reference scenario, please refer to technical report prepared by the Joint Global Change Research Institute, which is part of the Pacific Northwest National Laboratory. (See Docket EPA
- HQ - OAR 2009 - 0472 ) 2 For more informati on on the emissions reduction scenario, please refer to technical report prepared by the Joint Global Change Research Institute, which is part of the Pacific Northwest National Laboratory. (See Docket EPA
HQ - OAR - 2009 - 0472 )The program provides seven choices of constants for saltwater that are needed for the

calculations. We calculated pH values using all seven of these choices and found that in all cases the emissions reduc tions result in a 0.0014 increase in pH, with the exception of Roy et al. (1993) which calculated the emissions reductions as resulting in a 0.0013 increase in pH. The user is then prompted to choose which variables to calculate given user
- specified input variables. We chose to input total alkalinity (TA) and partial pressure of CO2 (pCO 2 ) in order for the program to output total inorganic CO 2 (TC) and pH. This was option 3 in the program’s menu. Additional inputs were then requested. For both scenarios we ran the model using a variet y of input values to test whether the model was sensitive to these inputs. We found that the model was not sensitive to these input values. The input values came from certified reference materials of sterilized natural sea w ater (Dickson, 2003, 2005, 2010). The inputs were as follows (The three values are for Dickson (2003, 2005, 2010) respectivel y):

 Salinity : 35.2, 31.6, 33.4  Total phosphate: 0.41, 0.33, 0.54 umol/kg;  Total silicate: 2.0, 2.6, 1.5 umol/kg  Input/output temp erature: 27°C, 27°C , 27°C 3 (characteristic tropical ocean temperature)  Input/output pressure: 0,0,0 dbar (surface pressure)  Total alkalinity

(TA): 2338, 2114, 2232 umol/kg  Partial Pressure (pCO2): 788.9 ppm (for the reference scenario) and 786 ppm (for the emissions reduction scenario) After all of this information was input into the model, it calculated the ocean pH for each set of input values. References A. G. Dickson. 1990. Thermody namics of the dissociation of boric acid in sy nthetic sea water from 273.15 to 318.15 K. Deep
- Sea Res. 37 , 755 - 766. Dickson, A. G. and F. J. Millero. 1987. A comparison of the equilibrium constants for the dissociation of carbonic acid in seawater media. Deep
- Sea Res. 34 , 1733 - 1743. (Corrigenda. Deep
- Sea Res. 36 , 983). Di ckson, A. G. 2003. Certificate of Analy sis

– Reference material for oceanic CO2 measurements (Batch #62, bottled on August 21, 2003). Certified by Andrew Dickson, Scripps Institution of Oceanography . November 21, 2003. Dickson, A. G. 2005. Certificate of Analy sis

– Reference material for oceanic CO2 measurements (Batch #69, bottled on January 4, 2005). Certified by

Andrew Dickson, Scripps Institution of Oceanography . July 12, 2005.
3 Even though the temperature ch anged between the reference and emissions reduction scenarios, we did not alter it as the model (and hence the pH) was not sensitive to the magnitude of temperature change computed.Dickson, A. G. 2009. Certificate of Analy sis

– Reference material for oceani c CO2

measurements (Batch #100, bottled on November 13, 2009). Certified by Andrew Dickson, Scripps Institution of Oceanograph y. February 10, 2010. Hansson, I. (1973) A new set of pH
- scales and standard buffers for seawater. Deep Sea Research , 20 : 479 - 491 . Khoo, K.H., R.W. Ramette, C.H. Culberson, and R. G. Bates. 1977. Determination of hydrogen ion concentrations in seawater from 5 to 40  C: Standard potentials at salinities from 20 to 45 ‰. Analytical Chemistry 49(1): 29
- 34. Lewis, E., and D. W. R. Wallac e. 1998. Program Developed for CO2 System Calculations. ORNL/CDIAC
- 105. Carbon Dioxide Information Analy sis Center, Oak Ridge National Laboratory , U.S. Department of Energy , Oak Ridge, Tennessee. Mehrbach, C., C. H. Culberson, J. E. Hawley , and R. N. Py tk owicz. 1973. Measurement of the apparent dissociation constants of carbonic acid in seawater at atmospheric pressure. Limnology and Oceanograph y 18 :897 - 907. Roy , R. N., L. N. Roy , K. M. Vogel, C. Porter
- Moore, T. Pearson, C. E. Good, F. J. Millero, and D. M. Campbell. 1993. The dissociation constants of carbonic acid in seawater at salinities 5 to 45 and temperatures 0 to 45 deg C. Marine Chemistry 44:249 - 267.

------- Erratum. 1994. Marine Chemistry 45:337.

-------- Erratum. 1996. Marine Chemistry 52:183.