Department of Pesticide Regulation 

Paul E. Helliker

Director M E M O R A N D U M 

Gray Davis 

Governor 

Winston H. Hickox 

Secretary, California Environmental 

Protection Agency

1001 I Street • P.O. Box 4015 • Sacramento, California 95812-4015 • www.cdpr.ca.gov

A Department of the California Environmental Protection Agency 

TO: John Sanders, Ph.D. 

Chief, Environmental Monitoring Branch 

FROM: Frank Spurlock, Ph.D. 

 Senior Environmental Research Scientist 

DATE: January 7, 2002 

SUBJECT: METHODOLOGY FOR DETERMINING VOC EMISSION POTENTIALS OF 

PESTICIDE PRODUCTS 

OVERVIEW

The purpose of this memorandum is to document changes made to the Department of Pesticide 

Regulation’s (DPR’s) procedures for estimating emission potentials (EP) of pesticide products. 

DPR uses EPs to calculate potential volatile organic compound (VOC) emissions from 

pesticides. 

BACKGROUND

The potential VOC emission of reactive organic gases (ROG) from a given application of a 

pesticide product is proportional to the product specific EP: 

potential VOC emission (pounds ROG) = (pounds product applied) x EP 

The EP is that fraction of a product that is assumed to contribute to atmospheric VOCs. 

Consequently, the accuracy of DPR’s annual estimated potential VOC emission inventory 

depends directly on the accuracy of EP values. The current “gold-standard” for determining EPs 

is thermogravimetric analysis (TGA; DPR, 1994). However, only about 30-40 percent of the 

total mass of applied pesticides that are included in DPR’s annual VOC inventory consists of 

products for which TGA EPs have been obtained. Other methods for estimating EPs have been 

devised for non-TGA products. These methods have included water and/or inorganic 

subtraction, where the entire product is assumed volatile except for the water and inorganic 

portion. The portion of nonvolatile components are determined using the product’s confidential 

statement of formula. Finally, EPs for many other products are assigned based on default EP 

values. 

Default EPs are defined based on formulation category (e.g., emulsifiable concentrate, flowable 

concentrate, dusts and powders) and have previously been arbitrarily defined in the past as the 

highest approved TGA EP in a formulation category. One rationale for setting the default EP to 

the high default value was to encourage pesticide registrants to voluntarily provide TGA data for 

their products. However, DPR receives TGA data for only a few products out of the many 

annually registered. The assignment of the arbitrary high default EP values is, therefore, 

ineffective for encouraging submission of TGA data. Further, the use of high default EP values 
John Sanders, Ph.D. 

March 27, 2002 

Page 2 

has been a significant source of error in previous VOC inventories because the high default EPs 

are inaccurate estimates of EP for those products that are assigned defaults. 

A second significant source of error in past inventories is from high-use products that have 

inaccurate or unrealistic EPs. One example is sodium chlorate cotton defoliant products. In 

2000, 11.3 million pounds of sodium chlorate were reported in the PUR. There are only a few 

sodium chlorate products with TGA data; EPs for these are zero or close to zero. However, 

historical estimated EPs for other sodium chlorate products based on water subtraction or 

water/inorganic subtraction methods range up to 82 per cent. As demonstrated later in this 

memorandum, sodium chlorate defoliant products do not contain VOCs, so that their EPs should 

actually be zero. Consequently, previous emission estimates for sodium chlorate products have 

been high by several million pounds. Other high-use product classes for which EP reevaluations are discussed in this memorandum include sulfur, petroleum oils, and metam 

sodium. 

Significant and variable sources of error in estimated VOC emissions prevent accurate evaluation 

of long-term emission trends, even though trend analysis is a stated goal of the VOC program 

(DPR, 1996). The purpose of this memorandum is to document recent changes in (1) the 

methodology for determining default EPs, and (2) EPs assigned to certain high-use product 

classes. The goal is to improve the accuracy and consistency of DPR’s VOC inventory 

estimates. 

DEFAULT EPs

The median is a common measure of central tendency in non-normal populations. VOC 

emission estimates using default EPs equal to the median TGA EP in a formulation class are 

more realistic than estimates based on the current extreme-value TGA EP defaults. Figure 1 

illustrates the distribution of TGA EPs for ten formulation classes. Using these data, default EPs 

for the formulation classes in Table 1 are now defined as the median TGA-based EP in each 

formulation category. One exception to this approach is pressurized products; there are no TGA 

data for pressurized products due to obvious technical difficulties in conducting TGA for 

pressurized products. Consequently, default EPs for all pressurized products are defined as 100. 
John Sanders, Ph.D. 

March 27, 2002 

Page 3 

TABLE 1. New default EPs for various formulation classes (December, 2001) 

Formulation 

Code Formulation 

New median 

TGA default EP

A0 DUST/POWDER 1.53 

B0 EMULSIFIABLE CONCENTRATE 39.15 

C0 FLOWABLE CONCENTRATE 4.80 

E0 GRANULAR/FLAKE 3.70 

H0 OIL 3.47 

J0 PELLET/TABLET/CAKE/BRIQUET 5.18 

K0 PRESSURIZED DUST 100†

L0 PRESSURIZED GAS 100†

M0 PRESSURIZED LIQUID/SPRAYS/FOGGERS 100†

N0 SOLUBLE POWDER 1.15 

O0 SOLUTION/LIQUID (READY-TO-USE) 7.30 

P0 WETTABLE POWDER 1.85 

R0 DRY FLOWABLE 1.02 

Q0 & S0 SUSPENSION & LIQUID CONCENTRATE 5.71‡

† default EP of all pressurized products defined as 100 

‡ Q0 and S0 formulation classes are combined due to (a) low number of Q0 products 

(n=6) and (b) no significant difference in median TGA for these formulation 

classes (Wilcoxon rank sum test, p = 0.8). 

RE-EVALUATIONS OF HIGH-USE PRODUCT CLASSES.

A. Sodium chlorate products 

Sodium chlorate defoliant products range from about 18 to greater than 50 percent (w/w) sodium 

chlorate. Sodium chlorate is an extremely strong oxidizing agent, and so is a fire hazard when in 

contact with organic chemicals (Eka Chemical, 2001; Merck Index, 1989). Sodium chlorate 

products are usually liquid formulations - no solid products have been reported used in the PUR 

since 1990. Confidential statements-of-formula (CSF) for sodium chlorate defoliant products 

show only water, aluminosilicates (clay), inorganic salts, and/or urea fire retardant (e.g., Drexel 

Chemical Co., 2001). Of these, urea is the only organic compound. Urea is highly polar, 

nonvolatile, hydrophilic, and has a very low Henry’s law constant (4.4 x 10-8 atm m3

 mol, 

UNEP\IRPTC, 2001). Urea, therefore, partitions into water or moist soil as opposed to the 

atmosphere. In addition, urea degrades rapidly to ammonia and carbon dioxide. Consequently, 

it is inappropriate to classify urea as a volatile organic compound. Therefore, all sodium chlorate 

defoliant formulations (active ingredient ≥ 18%) are now assigned an EP of zero in the absence 

of other information to the contrary. 
John Sanders, Ph.D. 

March 27, 2002 

Page 4 

B. Metam sodium products 

Metam sodium is a nonvolatile organic salt that is the active ingredient in numerous fumigant 

products. All metam sodium products are formulated and sold as concentrated aqueous solutions 

containing only metam sodium and water. However, when metam sodium is applied, the actual 

volatile fumigation agent is methyl isothiocyanate (MITC). MITC is a degradation product of 

metam sodium that is rapidly formed post-application. 

There are 3 metam sodium products for which TGA data have been reported. A previous strict 

interpretation of the TGA data for these products yields EP=0 because concentrated aqueous 

solutions of metam sodium are essentially nonvolatile under the experimental conditions of the 

TGA test. Obviously, the standard assumptions of the TGA test are invalid for metam sodium 

fumigant products. 

TGA data for ALL metam products will, henceforth, be disregarded, and metam sodium EPs will 

now be calculated on an “MITC-equivalent” basis based on product composition as follows: 

Assuming quantitative stoichiometric conversion of metam sodium to MITC 

following application, 1 gram of metam sodium yields 0.566 grams MITC. The 

“MITC-equivalent” EP for a metam sodium product containing X mass fraction 

metam sodium is then given as: 

product EP = 0.566 * X 

C. Sulfur products [≥ 50 percent sulfur and no other active ingredients]

Sulfur products typically account for more than 20 percent of the total mass of applied pesticide 

products in DPR’s annual pesticide use report (PUR); more than 69 million pounds of sulfur 

products were reported applied in the 2000 PUR. One consequence is that even small 

inaccuracies in high-use sulfur product EPs will lead to significant errors in estimated VOC 

emissions. 

Agricultural sulfur products are available in both solid (dust, wettable powder) and liquid 

(flowable, liquid concentrates) formulations. The solid formulations often contain nonvolatile 

diluents in addition to sulfur dust. These can include various clays, talc, or gypsum powders. In 

addition, wetting agents such as surfactants and/or detergents are added to dry wettable powder 

formulations to aid their mixing in solution. Such materials are typically high molecular weight 

and amphoteric, possessing very low or no volatility. The liquid formulations also contain 

similar components, but may also contain small amounts of high molecular weight thickeners 

such as xanthan gum. 
John Sanders, Ph.D. 

March 27, 2002 

Page 5 

Overall, sulfur products are expected to display very low volatility, as demonstrated by the 

available TGA data (figure 2a). It should also be noted that the TGA protocol for solids does not 

include a sample-drying step and does not account for the presence of absorbed water in the 

product (DPR, 1994). Because many of the sulfur products contain significant amounts of clay 

(capable of significant water absorption), it is expected that TGA values for such products are 

probably high biased in some cases. This bias may be as much as several percent depending on 

clay properties, percent composition, and ambient humidity. 

 

Based on the foregoing information, sulfur products for which (1) there are no TGA data, and (2) 

contain at least 50% sulfur, and (3) do not contain any other active ingredients are now assigned 

a default EP of 0.6, equal to the current sulfur TGA median. 

 

D. Petroleum oil (unclassified) and Mineral Oils [≥ 80 percent active ingredient]

Petroleum and mineral oils are similar to sulfur in that they represent very high pesticide use, 

nearly 25 million pounds in the 2000 PUR. In addition, many of the above types of oil products 

are classified as formulation category O0 (solution/liquid ready-to-use) or B0 (emulsifiable 

concentrate) instead of H0 (oils). This typically happens because registrants choose the 

formulation category when filling out the registration application and DPR does not have any 

requirements or strict guidelines for formulation category. The principal difficulty for VOC 

estimates is that default EPs for the three categories vary widely: 7.13, 39.15, 3.47 for 

formulation classes O0, B0, and H0, respectively. The use of defaults based on formulation 

codes results in a 10-fold range of variation in EPs. This decreases the accuracy of the VOC 

inventory and causes excessive year-to-year variability in the inventory when there are shifts in 

oil product use between formulation categories. 

The measured TGA EPs for petroleum oil (unclassified) and mineral oil are all quite low, with a 

median of 1.53 and a maximum of 6.03 (n=12, figure 2b). Consequently, petroleum oil 

(unclassified) or mineral oil products for which (1) there are no TGA data, and (2) contain at 

least 80% petroleum oil (unclassified) or mineral oil, and (3) do not contain any other active 

ingredients will now be assigned a default EP (= 1.53), equal to the oil median in Figure 2. 

SUMMARY

Several modifications to past procedures for assigning EPs to products without TGA data are 

detailed here; these changes will provide a more realistic estimate of pesticidal VOC emissions 

than in the past. The changes in EP estimation methods will commence with the VOC inventory 

conducted in December 2001. Additional EP re-evaluations will occur in the future as other 

refinements are developed. 
John Sanders, Ph.D. 

March 27, 2002 

Page 6 

REFERENCES CITED

DPR. 1994. Estimation of volatile emission potential of liquid pesticides by thermogravimetry. 

Environmental Monitoring Branch, Department of Pesticide Regulation. Sacramento, California. 

DPR. 1996. State Implementation Plan (SIP) for VOC Emissions from Pesticidal Applications. 

Department of Pesticide Regulation. Sacramento, California. 

Eka Chemicals. 2001. Sodium chlorate product information manual. Internet: 

http://www.ekachem.com/paper/bleaching//1.2.3.asp accessed December 15, 2001. 

Merck and Co. 1989. The Merck Index. Eleventh edition. 

Drexel Chemical Co. 2001. Material Safety Data Sheet for Defol 6W. Internet: 

<http://www.cdms.net/ldat/mp397002.pdf> accessed December 15, 2001. 

UNEP\IRPTC. 2001. United Nations Environment Programme, International Register of 

Potentially Toxic Chemicals. Screening Information Data Set (SIDS) for High Production 

Volume Chemicals. Volume 3. Internet: 

<http://www.chem.unep.ch/irptc/sids/volume3/tcontent.html> accessed December 15, 2001. 
n A0 Dusts/Powders 

A EPs (n=51)

ssion Potential

10 100

Formulation B0 Emulsifiable Concentrates

 TGA EPs (n=219)

Emission Potential

0.1 1 10 100

cumulative frequency 0.1 0.3 0.5

0.750.99

Formulation C0 Flowable Concentrate

 TGA EPs (n=46)

Emission Potential

0.1 1 10 100

cumulative frequency

0.10.30.5

0.750.95

E0 Granular/Flake

EPs (n=200)

ion Potential

10 100

Formulation J0 Pellet/Tablet/Cake

 TGA EPs (n=42)

Emission Potential

0.1 1 10 100

cumulative frequency

0.30.5

0.750.95

median = 5.18

median = 1.53

median = 3.70

median = 4.80 median = 39.2

. TGA EP distributions for various formulation classes

page 1 of figure 1

Formulation H0 Oil

 TGA EPs (n=9)

Emission Potential

0.1 1 10 100

cumulative frequency 0.3 0.5

0.750.95

median = 3.47
n N0 Soluble Powders

GA EPs (n=26)

ission Potential

10 100

Formulation O0 Soln/Liquid ready-to-use

 TGA EPs (n=169)

Emission Potential

0.1 1 10 100

cumulative frequency

0.10.30.5

0.750.95

Formulation P0 Wettable Powders

 TGA EPs (n=179)

Emission Potential

0.1 1 10 100

cumulative frequency 0.1 0.3 0.5

0.750.95

Formulation R0 Dry Flowable 

TGA EPs (n=38)

Emission Potential

.1 1 10 100

Formulation S0 Aqueous Concentrate

 TGA EPs (n=91)

Emission Potential

0.1 1 10 100

cumulative frequency

0.10.30.5

0.750.95

median = 1.2 median = 7.3 median = 1.9

median = 1.0 median = 5.7

page 2 of figure 1

GA EP distributions for various formulation classes (cont.)
Figure 2A. Distribution of TGA EPs for sulfur products 

[ ≥ 50% sulfur, no other organic active

 ingredients, n=27]

Emission Potential

0.1 1 10 100

cumulative frequency

0.1

0.3

0.5

0.7

0.95

Figure 2B. Distribution of TGA EPs for petroleum oil 

(unclassified) and mineral oil [ ≥ 80% oil, no 

other organic active ingredients, n=12]

Emission Potential

0.1 1 10 100

cumulative frequency

0.1

0.3

0.5

0.7

0.95

median = 0.6

median =1.53