October 17th

, 2007

Re: uncertainty in VOC inventory from MUF and AMAF estimates

Brent Newell

Center on Race, Poverty and the Environment

47 Kearny Street, Suite 804

San Francisco, CA 94108

Dear Brent:

PANNA and CRLAF staff members have reviewed the method use fraction (MUF) and 

application method adjustment factor (AMAF) estimates that underlie DPR’s VOC inventory

calculations.

1 In DPR’s proposed regulations, these estimates determine the amount that the

inventories have to be reduced. We would like to bring the following points involving these

estimates to your attention:

1. MUFs for the 1991 and 2004 inventories do not have a foundation in PUR reports.

2. Validity of the MUFs for the 1991 baseline inventory for all fumigants but 1,3-

dichloropropene are not verifiable.

3. Field studies of AMAFs have highly variable results even among similar studies and are

therefore manifestly highly uncertain.

4. Previous reviews

2,3 have noted uncertainties in AMAF estimates and concluded that some

AMAFs proposed by DPR were not conservative enough.

The above uncertainties are important to note because DPR’s approach to meeting its VOC

inventory commitments relies principally on adjustments based on estimates of movement

towards application methods with smaller AMAFs. These adjustments are being used to offset

large increases in pesticide use that have occurred since 1991. Using these adjustments, for

Ventura, the commitment to reduce VOC inventories is being lessened by 4 tons/day, and for San

Joaquin, the commitment to reduce VOC inventories is being lessened by 6.5 tons/day.

4

Because of the chosen approach and the above points, we do not have confidence that the actual

VOC inventory reductions will be as large as those estimated by DPR. An approach that instead 
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relied principally on reductions in pesticide use would have far less dependence on the highly 

uncertain AMAF and MUF estimates.

We hope the above summary is helpful for your analysis of the 1994 SIP implementation. More

detail on each of the above points is in the following sections.

Sincerely yours,

SIGNED COPY ON FILE

Brian R. Hill, PhD

PANNA

49 Powell Street, Suite 500

San Francisco, CA 94102

(415) 981-1771 x321

bhill@panna.org

Anne Katten, MPH

CRLA Foundation

2210 K Street, Suite 201

Sacramento, CA 95816

(916) 446-7904 x19

akatten@cal.net
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1. MUFs for the 1991 and 2004 inventories do not have a foundation in PUR

reports.

As noted in the memo from Barry, Spurlock and Segawa to Sanders,

5

The PUR database includes the identity of the product applied, the amount

applied, location, date, crop/site treated, and other information. DPR uses the

pounds of product applied recorded in [the] PUR database to calculate the VOC

emissions for each pesticide application included in the pesticide VOC emission 

inventory. [The] PUR database contains general information about the application

method (i.e. air, ground, or other), but it does not indicate the specific application 

method. Therefore, another adjustment is needed to account for the use of each

fumigant application method. DPR [proposed] regulation 07-002 contains

provisions to include method of application for field fumigations in PURs, so the

procedure outlined here will not be used in the future. [emphasis added]

The proposed provisions to include method of application for field fumigants will be valuable in

the future. They would be even more valuable to understanding fumigant usage patterns if they

are applied state-wide rather than just in the current non-attainment areas, as currently proposed 

in DPR regulation 07-002. However, historically, the PUR reports provide no foundation for

distinguishing between the various methods of application, as noted by DPR in the emphasized 

sentence above.

2. Validity of the MUFs for the 1991 baseline inventory for all fumigants

but 1,3-dichloropropene is not verifiable.

For estimates of MUFs for metam applications, DPR’s citation reads “Lawson (2006) provides

a survey of metam-sodium practices,”

6 but there is no entry in their bibliography corresponding

to “Lawson (2006).” DPR notes that,

Several commentors objected to the use of the undocumented method use fractions

for metam. DPR does not normally use undocumented data. However, in this case

the registrants’ information and professional judgment are likely more reliable than 

DPR’s, and DPR has employed the suggested method use fractions. At DPR’s

request, the registrants have agreed to provide documentation on the method use

fractions.

The MUFs for metam applications remain essentially undocumented.

For estimates of MUFs for methyl bromide, DPR relies entirely on an analysis from the

Consortium of Methyl Bromide Registrants.

7 For estimates of MUFs for chloropicrin

applications, DPR relies entirely on an analysis and a letter from the Chloropicrin Manufacturers
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Task Force.

8,9 From these analyses of MUFs for methyl bromide and chloropicrin, DPR simply

asserts as “assumptions:”10

• For 1990/91 methyl bromide and chloropicrin applications, one-half of all strawberry, row,

vegetable, and nursery crops were fumigated using a shallow injection broadcast method 

with a high permeability tarpaulin or no tarpaulin, and one-half were conducted with a

shallow injection bed method and a high permeability tarpaulin.

• For 1990/91 methyl bromide and chloropicrin applications, all tree and vine crops were

fumigated using a deep injection method with a high permeability tarpaulin or no tarpaulin.

Since high-permeability tarps have no significant effect on emissions, the above assumptions are

equivalent to simply assuming that 100% of methyl bromide and chloropicrin applications in the

1991 baseline year were untarped.

Only for 1,3-dichloropropene does DPR have a quantitative, historically-documented MUF

estimate. This is largely because no use was allowed in California between 1991-1994, and since

1995 the registrant has records of the specific application method, which they are required to 

maintain.

11

3. Field studies of AMAFs have highly variable results even among similar

studies and are therefore manifestly highly uncertain.

As an example of the strong dependence on actual field conditions or other unknown factors,

consider the MITC emission estimates.

12 For the three studies of drip emissions, the fraction of

MITC emitted from the soil is estimated at 2.4%, 4.4% and 20.5%, respectively. Whether

weather, soil conditions or other undetermined variables are responsible for these variations is

less important than the fact that this is a more than eight-fold variation. In the face of this

uncertainty, DPR averages the results to get 9% for the AMAF. As another example, consider

the surface Dazomet studies. The fraction of MITC emitted from the soil is 2.3%, 4.57% and 

42.9%, respectively. This is a more than eighteen-fold variation. DPR averages the result to get

17% as the AMAF.

The above variations are by themselves sufficient to demonstrate the high uncertainty in 

estimating AMAFs.

4. Previous reviews have noted uncertainties in AMAF estimates and

concluded that some AMAFs proposed by DPR were not conservative

enough.

Sharon Papiernik of the USDA performed a peer review of the AMAFs.

13 Additional sources of

uncertainty and lack of conservatism in the estimates of the AMAFs were detailed in an earlier

memo to you from Susan Kegley of PANNA.

14
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Papiernek observed that the amount of water required per water application in the original

proposed regulation (0.25 inches) was quite low compared to the amount typically added in

research studies (about 0.5 inches per application). She concluded that with this low amount of

water it is not known whether use of the emission adjustment factors from experimental studies

is appropriate. In the revised proposed regulation only 0.2 inches of water is to be required per

water application. In addition, the required number of post-application waterings for metam

applications is reduced from three to two waterings based on a registrant study which has not yet

been coumpletely reviewed or found acceptable by DPR.

15 DPR does not provide any 

explanation of how they reconcile this proposed change with Papiernik’s observations and 

concerns.

Papiernik observed that many field studies were conducted under conditions not representative

of California. In particular she observed that the 1,3-dichloropropene deep injection studies were

conducted under unrepresentative cool conditions and that higher emissions would typically be

expected in California. Despite this observation, DPR has decided to group the 1,3-

dichloropropene studies by depth as recommended by industry.

16 This decreases the AMAF for

deep 1,3-dichloropropene applications from 41% to 26%.

Papiernik concluded that the AMAF of 48% for broadcast fumigation with methyl bromide using

HDPE tarp wasn’t supported by the data or conservative enough because average of all studies

was 52% and range was from less than 30% to over 80%. DPR has not revised the AMAF or

even stated that they are considering revising this AMAF.

17

For sodium tetrathiocarbonate, Papiernik concluded that the proposed 10% AMAF was not

conservative enough because flux was still rising at 10% emissions when monitoring was halted 

on the study. DPR has stated that this estimate may underestimate total emissions but has not

revised the AMAF.

18

Papiernik agreed with DPR that the high emission factors for methyl bromide bedded fumigation

and bare soil applications were scientifically supported. In contrast, industry representatives

have characterized these emission factors as overly conservative.

We note that based at least in part on Papiernik’s observation that no experimental evidence was

cited to support the originally proposed AMAF for chloropicrin applications followed by water

treatments, DPR has increased the AMAF significantly for chloropicrin applications followed by 

three water treatments.

19

However, in contrast, while Papiernik observed that the proposed 

AMAF for chloropicrin drip applications of 15 percent was lower than either the 18 percent

emissions measured in Georgia or the 32% emissions measured in Florida trials, DPR has now

revised the chloropicrin drip AMAF downward to 12 percent.

20

Collectively, such sources of uncertainty contribute to substantial uncertainty in both the 1991 

baseline and 2004 inventories, and to overestimates of emission reductions achievable through

changes in application method.
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References 1 Memorandum from Terrell Barry, Frank Spurlock and Randy Segawa to Sanders, September 29,

2007, http://www.cdpr.ca.gov/docs/emon/pubs/ehapreps/analysis_memos/1955_sanders.pdf. 2 Memorandum from Susan Kegley to Brent Newell, attached as Exhibit 3 of letter from Brent

Newell, Center on Race, Poverty and the Environment to Robert J. Sawyer, Chairman, California

Air Resources Board, June 12, 2007. 3 Letter from Sharon K. Papiernek, Research Soil Scientist, USDA, to Randy Segawa, August 3,

2007.

4 For Ventura, compare the unadjusted 2004 inventory of 9.3 tons/day with the corresponding

target of 3.1 tons/day (Reference 1, Table 21). The 2004 inventory is 6.2 tons/day over target. If

instead, the adjusted inventories are used, the 2004 inventory is 4.8 tons/day and the target is 2.6 

tons/day (Reference 1, Table 23). So after adjustments, the 2004 inventory is 2.2 tons/day over

target. In other words, for Ventura, the commitment to reduce VOC inventories is being lessened 

by 4 tons/day (2.2 tons/day instead of 6.2 tons/day) through these adjustments. For San Joaquin,

the commitment to reduce VOC inventories is being lessened by 6.5 tons/day. 5 Ibid 1, p. 18.

6 Ibid 1, p. 19.

7 Stangellhini, M., “Analysis of Methyl Bromide emissions in the San Joaquin Valley in 1990 and

2004.” Consortium of Methyl Bromide Registrants. Documented submitted to DPR in May

2006.

8 Stangellhini, M., “Analysis of Chloropicrin emissions in the San Joaquin Valley in 2990 and 

2004." Chloropicrin Manufacturers Task Force. Document submitted to DPR in May 2006.

9 Letter from Stephen Wilhelm to Randy Segawa, September 26, 2007, Chloropicrin 

Manufacturers Task Force. 10 Ibid 1, p. 19.

11 Telone use was cancelled in 1991-1994 so the 1991 baseline is zero. Dow adopted the record 

keeping requirement as part of the conditions of resuming use starting in 1995 so there is method 

specific data that could be used for later inventories. 12 Ibid 1, Table 5.

13 Ibid 3.

14 Ibid 2.

15 Ibid 1, p. 12.

16 Ibid 1, p. 16.

17 Ibid 1, pp. 6-7.

18 Ibid 1, p. 15.

19 Ibid 1, p. 10.

20 Ibid 1, pp. 10-11.