									

MEMORANDUM

To:	Erin Birgfeld 

Cc:	Margaret Sheppard

From:	Sarah Percy, Mark Wagner

Date:	July 15, 2003

Re:	Revised Evaluation of the Global Warming Potential for n-Propyl
Bromide 

Deliverable under EPA Contract Number 68-D-00-266, Work Assignment 2-05
Task 03



Based on analysis developed by ICF’s subcontractor, Dr. Don Wuebbles,
please find a revised discussion of the 100-year integration Global
Warming Potential (GWP) for n-propyl bromide (nPB). Please contact Mark
Wagner at (202) 862-1155 if you have any questions.  

Summary

Based on an analysis of a cooperative research effort by Atmospheric and
Environmental Research, Inc. (AER) and the Center for Chemical and
Environmental Physics at Aerodyne Research, Inc, and estimates on the
reaction products of nPB, it was determined that the chemical has a GWP
of about 1.57.  Although, the value could be slightly less depending on
the amount of rainout removal of nPB reaction products containing carbon
or slightly larger due to radiative forcing of the reaction products.

Discussion of Results

In reviewing literature, the website for the Albemarle Corporation
presents a GWP, Halocarbon GWP (HGWP), Atmospheric Lifetime, and Ozone
Depletion Potential for nPB (  HYPERLINK
"http://www.albemarle.com/abzregstatus.htm" 
http://www.albemarle.com/abzregstatus.htm ).  The calculations were
carried out in a cooperative effort by AER and the Center for Chemical
and Environmental Physics at Aerodyne Research, Inc.

The GWP is calculated relative to CO2, while the HGWP is calculated
relative to CFC-11. GWP calculations were made using different
integration time horizons.   By the HGWP method, CFC-11 is ten thousand
times more detrimental as a global warming agent than is n-propyl
bromide.  By the GWP method, it is fourteen thousand times worse than
n-propyl bromide, and n-proply bromide is only one tenth as detrimental
as CO2.  Table 1 compares the HGWP and GWP for CFC-11 and nPB.

Table 1: Global Warming Potentials for CFC-11 and n-Propyl Bromide 

Compound	HGWP	GWP

(20 yrs)	GWP

(100 yrs)	GWP

(500 yrs)

CFC-11	1.0	4500	3400	1400

n-Propyl Bromide	0.0001	1.01	0.31	0.1



The analysis by AER and Aerodyne thus appears to be the basis for the
GWP of 0.31 for nPB.  Based on the references on the website (which
cites work by Dr. Don Wuebbles on the ODP of nPB as, “in press”),
this analysis was likely done around 1997. Other companies’ websites
suggest the same GWP and HGWP values, although, in some cases, the GWP
is listed as zero.

A published paper on nPB written by AER and Aerodyne has not been found,
which suggests that their analysis was conducted specifically for
Albemarle or some other company. Nonetheless, both AER and Aerodyne are
highly respected research groups. It can be assumed that Aerodyne
measured the infrared absorption spectra for nPB, and AER used their
radiative transfer model to evaluate the radiative forcing and GWPs.

Therefore, it is expected that the estimates are reasonably accurate
except that the listed atmospheric lifetime of nPB on the Albemarle
website is 11 days, smaller than the published evaluation (approximately
19 days, Wuebbles et al., 2001). Nonetheless, the evaluation for the
direct GWP for nPB of 0.31 is accepted within a factor of two. The
direct GWP for nPB, therefore, is better approximated as 0.5.  A
reevaluation of the direct GWP using the longer ALT could be undertaken
to confirm the approximated value, but probably is not necessary.  

However, this direct GWP evaluation does not consider the reaction
products of nPB, particularly the three carbon atoms that, except for
any rainout of the reaction products containing carbon, eventually will
become carbon dioxide. Modeling has not been used to determine how the
rainout process removes carbon-containing products (focus in those
studies was on bromine reaching the stratosphere). 

Ignoring any rainout of reaction products containing carbon, the
reaction products will contribute an additional (indirect) GWP due to
the production of CO2 equal to about 1.07.  This value could be slightly
larger due to the radiative forcing of reaction products before the
final production of carbon dioxide or somewhat less depending on the
amount of rainout removal of nPB reaction products containing carbon. 
The GWP of 1.07 is based on the following calculation:

1 kg of nPB	1000 g of nPB	1 mol of nPB	3 mol of CO2	44 g of CO2	1 kg of
CO2	= 1.07 kg CO2

 	1kg of nPB	123 g of nPB	1 mol of nPB	1 mol CO2	1000 g of CO2

	

Adding the direct and indirect GWPs, the 100-year integration GWP for
nPB is estimated at 1.57. 

