MEMORANDUM

To: Margaret Sheppard , U.S. EPA

Cc: Yaidi Cancel, U.S.EPA

From: Emily Herzog, Ed Carr, Mark Wagner, ICF International 

Date: May 21, 2010

Re: Sensitivity Analysis CMAQ results on projected maximum TFA rainwater concentrations and 

maximum 8-hr ozone concentrations (Deliverable under EPA Contract Number EP-W-06-008 

Task Order 038, Task 06)

In addition to updating the baseline analysis for the Assessment of the Potential Impacts of HFO-1234yf 

and the Associated Production of TFA on Aquatic Communities and Local Air Quality, ICF conducted a 

sensitivity analysis based on the findings of Papasavva et al. as described in their 2009 paper Estimated 

2010 Refrigerant Emissions of 2,3,3,3-tetrafluoropropene (HFC-1234yf) in the United Stated Resulting 

from Automobile Air Conditioning. This memorandum summarizes the results from the sensitivity 

analysis and provides a comparison of the results with the baseline analysis as well as with the findings of 

Luecken et al. (2010).

Please contact Mark Wagner at 202-862-1155 with any questions or comments.
1

Assessment of Potential HFO-1234yf Emissions

The following section describes the assumptions used to determine potential emissions of HFO-1234yf.

Scenarios of HFO-1234yf Market Penetration

For the Assessment of the Potential Impacts of HFO-1234yf and the Associated Production of TFA on 

Aquatic Communities, Soil and Plants, and Local Air Quality, two scenarios were developed. Both 

scenarios assume that HFO-1234yf is used as a drop-in replacement for HFC-134a,1 with a replacement 

ratio of 1:1 HFC-134a to HFO-1234yf.2 

 Scenario 1: HFO-1234yf is used in the United States as a new car refrigerant in the MVAC sector. 

HFO-1234yf begins penetrating the market in 2016 reaching 100 percent market penetration by 

2020, as described in Table 1 below. 

 Scenario 2: HFO-1234yf is used in the United States as a new car refrigerant in MVAC systems, 

refrigeration, and stationary AC systems. Similar to scenario 1, by 2020, HFO-1234yf is used in all 

new MVAC systems. For refrigeration and stationary AC systems, HFO-1234yf enters the market 

in 2010, reaches 30 percent penetration of the market in 2015, and 100 percent by 2020. 

The market penetration scenarios are summarized in Table 1 below.

Table 1: Summary of Assumed Penetration of HFO1234yf in Scenarios Used in Analysis*

Sectors 2010 2015 2020

Scenario 1

MVACs 0% 0% 100%

Scenario 2

MVACs 0% 0% 100%

Refrigeration 6% 30% 100%

Stationary Air Conditioning 6% 30% 100%

*The dates of introduction of HFO-1234yf are consistent with the earlier analysis, conducted in 2009. 

The specific dates of introduction are used as a demonstration of how HFO-1234yf might be phased in; 

actual dates may differ by several years. Examining the period from initial introduction of the 

refrigerant to market saturation allows the analysis to consider potential impacts of HFO-1234yf in the 

near-term (i.e., 10 - 15 years), during which time there are already specific State goals for ground-level 

ozone impacts. In addition, the analysis considers the potential longer term impacts of HFO-1234yf after 

the refrigerant has saturated the market, assuming continued growth in use.

HFO-1234yf Emission Assumptions

For the sensitivity analysis, emission assumptions were based on the findings of Papasavva et al. (2009) 

regarding the emission projections of HFO-1234yf from the MVAC sector. In contrast, ICF assumed that 

 

1

In all scenarios, HFO-1234yf replaces only pure HFC-134a, not any blends with HFC-134a as a component.

2 The ratio of HFC-134a to HFO-1234yf has been estimated at 1:0.9, however a 1:1 ratio was used to provide a 

worst case estimate.
2

emissions of HFO-1234yf will be equivalent to emissions of HFC-134a for the baseline analysis. Emission 

assumptions for both the baseline analysis and the sensitivity analysis are summarized below in Table 2.

Table 2: Refrigerant Loss Assumptions for Baseline and Sensitivity Analysis

Assumption Baseline Analysisa Sensitivity Analysis

Leak Rate 8% 5.6%

Servicing Leaks (annualized) 10% 3.2%

End-of-life Loss Rate 42.5% 42.5%

a HFC-134a MVAC assumptions from the U.S. EPA Vintaging Model, Version VM IO File v4.4_12-16-09. 

For both analyses, emissions of refrigerant due to servicing motor vehicle air conditioning systems were 

expected to be higher during the spring and summer, with up to 80% of emissions due to repairs 

occurring from April through August.3 Furthermore, refrigerant emissions from servicing motor vehicle 

air conditioning systems were estimated at 47% of annual refrigerant emissions from motor vehicles.4 

As a result, the analysis assumes that 59.5% of annual emissions of HFO-1234yf would occur from April 

through August, with 11.9% of annual emissions occurring during each of those five months. The 

remaining 40.5% of annual emissions was modeled to occur from September through March, with 5.8% 

of annual emissions occurring during each of those seven months. This assumption was also applied to 

stationary AC end uses based on the assumption that similar patterns of seasonal emissions would be 

attributable to this end-use.

Estimated Emissions of HFO-1234yf

Using EPA’s Vintaging Model, ICF estimated emissions of HFO-1234yf for both scenarios using both sets 

of emission assumptions. These estimates are summarized in Table 3 while estimated monthly emission 

estimates of HFO-1234yf for the year 2050 are provided in Table 4. Complete tables with estimated 

annual emissions can be found in Annex A and Annex B. 

Table 3: Summary of Estimated Emissions of HFO-1234yf (MT)*

Scenarios 2020 2030 2040 2050

Baseline Analysis 

Scenario 1 (MVAC) 6,244 28,327 33,093 35,851

Scenario 2 (All Ref and AC) 10,501 43,296 55,070 60,616

Sensitivity Analysis 

Scenario 1 (MVAC) 3,053 15,349 18,841 20,411

Scenario 2 (All Ref and AC) 7,309 30,318 40,817 45,175

* ICF projected emissions of HFO-1234yf using special scenarios designed specifically for this analysis and run on 

the U.S. EPA Vintaging Model, Version VM IO File v4.4_12-16-09. 

Table 4: Summary of Estimated Monthly Emissions of HFO-1234yf in 2050 (MT)

Scenarios Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Baseline Analysis 

Scenario 1 (MVAC) 2,074 2,074 2,074 4,266 4,266 4,266 4,266 4,266 2,074 2,074 2,074 2,074

Scenario 2 (All Ref and AC) 4,025 4,025 4,025 6,489 6,489 6,489 6,489 6,489 4,025 4,025 4,025 4,025

Sensitivity Analysis 

Scenario 1 (MVAC) 1,181 1,181 1,181 2,429 2,429 2,429 2,429 2,429 1,181 1,181 1,181 1,181

Scenario 2 (All Ref and AC) 3,131 3,131 3,131 4,651 4,651 4,651 4,651 4,651 3,131 3,131 3,131 3,131

 

3 Hoffpauir, Elvis. 2009. Email to Karen Thundiyil, 10 March.

4 U.S. EPA Vintaging Model, Version VM IO File v4.2 10-07-08
3

Figure 1, Figure 2, and Figure 3 graphically depict the estimated annual HFO-1234yf emissions for each 

scenario. Figure 4 graphically depicts the estimated 2050 monthly HFO-1234yf emissions for each 

scenario. 

Figure 1: Estimated Emissions of HFO-1234yf by End-Use Sector under the Baseline Analysis (MT)

Figure 2: Estimated Emissions of HFO-1234yf by End-Use Sector under the Sensitivity Analysis (MT)
4

Figure 3: Estimated Annual Emissions of HFO-1234yf under All Scenarios (MT)

Figure 4: Estimated Monthly Emissions of HFO-1234yf under All Scenarios in Year 2050 (MT)
5

Results of the Sensitivity Analysis

Using EPA’s CMAQ model version 4.7, a one-year simulation was performed using 2001 meteorological 

data to project maximum monthly TFA rainwater concentrations, monthly maximum dry deposition of 

TFA, and maximum 8-hr ozone concentrations for the Los Angeles and Houston regions resulting from 

emissions of HFO-1234yf from those regions only. These regions were chosen based on the potential 

presence of vernal pools, their susceptibility to high TFA deposition concentrations, and their continuing 

and chronic problem with high levels of ground level ozone. The model used the extended version of 

the carbon bond five chemical mechanism as developed by Luecken et al. (2010), which incorporates the 

gaseous and aqueous chemistry of HFO-1234yf and its products. In ICF’s Assessment of the Potential 

Impacts of HFO-1234yf and the Associated Production of TFA on Aquatic Communities, Soil and Plants, 

and Local Air Quality (2010) results from the baseline analysis are presented. The results for the 

sensitivity analysis are summarized below. 

TFA Rainwater Concentrations

Monthly maximum average TFA rainwater concentrations for each region under each scenario are 

summarized in Table 5.

Table 5: Summary of Estimated Monthly Average TFA Rainwater Concentrations in 2050 (ng/L)

Region Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Sensitivity Analysis, Scenario 1

Los Angeles 59 21 109 108 497 572 363 484 107 78 128 61

Houston 12 14 21 17 26 38 54 30 28 12 10 17

Sensitivity Analysis, Scenario 2

Los Angeles 130 47 240 240 1099 1267 803 1072 237 173 283 136

Houston 26 30 46 38 57 85 120 67 63 27 23 38

Under scenario 1 for the sensitivity analysis, the results indicate that the maximum monthly average TFA 

rainwater concentration in the Los Angeles region in 2050 is 572 ng/L, while the maximum monthly 

average TFA rainwater concentration in the Houston region in 2050 is 54 ng/L. Under scenario 2 for the 

sensitivity analysis, the results indicate that the maximum monthly average TFA rainwater concentration 

in the Los Angeles region in 2050 is 1,267 ng/L, while the maximum monthly average TFA rainwater 

concentration in the Houston region in 2050 is 120 ng/L. 

Similar to the baseline analysis, for Los Angeles, June represents the month with the highest projected 

monthly average TFA rainwater concentration, while for Houston, July represents the month with the 

highest projected monthly average TFA rainwater concentration. The monthly average maximum TFA 

rainwater concentrations for these two peak months are geographically depicted below in 
6

Figure 5 and Figure 6, for both scenarios, for Los Angeles and Houston, respectively. 
7

Figure 5: June 2050 Los Angeles Sensitivity Analysis Scenario 1 and Scenario 2 Results 

 

Figure 6: July 2050 Houston Sensitivity Analysis Scenario 1 and Scenario 2 Results 

 

TFA Dry Deposition

Table 6 presents the results of both the maximum annual and monthly maximum TFA deposition

expressed on an annual basis. 

Table 6: Summary of Estimated TFA Dry Deposition in 2050 

Notes: Formula weight of TFA is 114 g/mole.

a Maximum concentration occurred in May for Los Angeles and in July for Houston. Results are expressed on 

annual basis using the peak monthly deposition rate times 12. 

TFA Maximum Monthly Averagea TFA Maximum Annual Average

nmole/m2-yr g/m2-yr nmole/m2-yr g/m2-yr

Sensitivity Analysis, Scenario 1

Los Angeles 8,698 323 2,188 81

Houston 1,455 54 534 20

Sensitivity Analysis, Scenario 2

Los Angeles 16,686 619 4,745 176

Houston 2,813 104 1,148 43
8

Ground Level Ozone Concentrations

Under scenario 1 for the sensitivity analysis, results for the Los Angeles and Houston regions show a 

maximum increase in the 8-hr ozone concentration of 0.030 ppb and 0.009 ppb, respectively. Under 

scenario 2 for the sensitivity analysis, results for the Los Angeles and Houston regions show a maximum 

increase in the 8-hr ozone concentration of 0.057 ppb and 0.016 ppb, respectively. Assuming an 8-hr 

ozone standard of 75 ppb, HFO-1234yf is projected to contribute to a maximum of roughly 0.04 –

0.076% of total ground-level ozone in Los Angeles and 0.012 – 0.021% and of total ground-level ozone in 

Houston. Maximum increases in 8-hr ozone concentrations are geographically depicted in

Figure 7,

Figure 8, and Figure 9.

Figure 7: LA May 22, 2050 Sensitivity Analysis Scenario 1 and Scenario 2 Results

 

Figure 8: Houston June 11, 2050 Sensitivity Analysis Scenario 1 and Scenario 2 Results

 

Figure 9: Houston August 29, 2050 Sensitivity Analysis Scenario 1 Results
9

 
10

Comparison of Results

For comparison purposes, the following table summarizes results of the baseline analysis, the sensitivity 

analysis, and Luecken et al. (2010). 

Table 7: Comparison of Results for Southern California

Analysis Maximum Projected TFA 

Rainwater Concentration (ng/L)

Maximum Estimated TFA 

Dry Deposition (g/m2)*

Maximum Increase in 8-hr 

Ozone Formation

Baseline, Scenario 1 1,116 143 0.07%

Baseline, Scenario 2 1,700 237 0.11%

Sensitivity, Scenario 1 572 81 0.04%

Sensitivity, Scenario 2 1,267 176 0.08%

Luecken et al. (2010) 1,264 240 0.1%

*ICF results represent the annual average maximum for Southern California, while Luecken’s results represent the 

2.5 month spatial average. For Southern California, Luecken’s results show TFA dry deposition to be about 150 

g/m2.

The relationship between HFO-1234yf emissions and projected maximum TFA rainwater concentrations for both 

regions are also displayed below in Figure 10 and 

Figure 11. 

Figure 10: Relationship between HFO-1234yf emissions and maximum TFA rainwater concentrations in LA
11

Figure 11: Relationship between HFO-1234yf emissions and maximum TFA rainwater concentrations in Houston

As shown above, the relationship between HFO-1234yf emissions and TFA rainwater concentrations 

appears to be relatively linear. To support this relationship, the data for each region were fitted to a 

linear regression model. The equations for each regression model are as follows:

Los Angeles TFA Rainwater Concentration = 51.55 + (HFO-1234yf Emissions * 0.027)

Houston TFA Rainwater Concentration = 4.64 + (HFO-1234yf Emissions * 0.0026)

The equations above can be used to estimate TFA rainwater concentration projections for other HFO1234yf emission scenarios. However, it must be noted that the equations assume that the current 

chemical mechanism of gas-phase and aqueous chemistry of HFO-1234yf and its products remains 

substantially the same in future analyses. Also, it is possible that results may differ if other 

meteorological datasets (e.g., 2005) or higher spatial resolutions (e.g., 12-km) were used in the original 

analysis. Finally, due to localized variability in meteorology and emission distributions, these results 

cannot be applied to other regions of the U.S. 
12

Annex A: Annual HFO-1234yf Emissions Estimated under Each Scenario 

for the Baseline Analysis for Years 2010 through 2050 (MT)*

Year

Baseline Scenario 1 Baseline Scenario 2

MVACs MVACs Refrigeration Stationary AC TOTAL

2010 - - 39 7 46

2011 - - 111 20 132

2012 - - 218 40 258

2013 - - 361 66 426

2014 - - 541 98 640

2015 - - 762 138 900

2016 407 407 1,093 196 1,696

2017 1,229 1,229 1,541 273 3,043

2018 2,472 2,472 2,110 369 4,951

2019 4,143 4,143 2,807 485 7,435

2020 6,244 6,244 3,636 620 10,501

2021 8,332 8,332 4,487 766 13,585

2022 10,413 10,413 5,389 916 16,718

2023 12,513 12,513 6,278 1,066 19,857

2024 14,644 14,644 7,209 1,216 23,069

2025 16,812 16,812 8,128 1,367 26,307

2026 19,003 19,003 9,043 1,516 29,561

2027 21,203 21,203 9,953 1,678 32,834

2028 23,962 23,962 10,914 1,848 36,724

2029 26,335 26,335 11,817 2,017 40,170

2030 28,327 28,327 12,748 2,221 43,296

2031 29,926 29,926 13,591 2,412 45,929

2032 31,118 31,118 14,348 2,577 48,043

2033 31,295 31,295 14,918 2,720 48,932

2034 31,514 31,514 15,479 2,861 49,854

2035 31,791 31,791 15,924 3,010 50,725

2036 32,084 32,084 16,382 3,213 51,678

2037 32,374 32,374 16,824 3,408 52,606

2038 32,627 32,627 17,249 3,592 53,468

2039 32,857 32,857 17,656 3,767 54,280

2040 33,093 33,093 18,046 3,931 55,070

2041 33,345 33,345 18,371 4,008 55,724

2042 33,637 33,637 18,668 4,080 56,385

2043 33,906 33,906 18,921 4,151 56,977

2044 34,177 34,177 19,156 4,217 57,549

2045 34,450 34,450 19,374 4,278 58,102

2046 34,726 34,726 19,566 4,315 58,606

2047 35,004 35,004 19,756 4,351 59,110

2048 35,284 35,284 19,944 4,383 59,611

2049 35,566 35,566 20,132 4,415 60,112

2050 35,851 35,851 20,318 4,447 60,616

* ICF projected emissions of HFO-1234yf using special scenarios designed specifically for this analysis and 

run on the U.S. EPA Vintaging Model, Version VM IO file v4.4_12-16-09.
13

Annex B: Annual HFO-1234yf Emissions Estimated under Each Scenario 

for the Sensitivity Analysis for Years 2010 through 2050 (MT)*

Year

Sensitivity Scenario 1 Sensitivity Scenario 2

MVACs MVACs Refrigeration Stationary AC TOTAL

2010 - - 39 7 46

2011 - - 111 20 132

2012 - - 218 40 258

2013 - - 361 66 426

2014 - - 541 98 640

2015 - - 762 138 900

2016 199 199 1,093 196 1,488

2017 601 601 1,541 273 2,415

2018 1,209 1,209 2,110 369 3,688

2019 2,026 2,026 2,807 485 5,317

2020 3,053 3,053 3,636 620 7,309

2021 4,073 4,073 4,487 766 9,326

2022 5,091 5,091 5,389 916 11,396

2023 6,118 6,118 6,278 1,066 13,461

2024 7,159 7,159 7,209 1,216 15,584

2025 8,219 8,219 8,128 1,367 17,714

2026 9,290 9,290 9,043 1,516 19,849

2027 10,366 10,366 9,953 1,678 21,997

2028 12,206 12,206 10,914 1,848 24,968

2029 13,868 13,868 11,817 2,017 27,702

2030 15,349 15,349 12,748 2,221 30,318

2031 16,647 16,647 13,591 2,412 32,650

2032 17,749 17,749 14,348 2,577 34,674

2033 17,819 17,819 14,918 2,720 35,456

2034 17,918 17,918 15,479 2,861 36,259

2035 18,077 18,077 15,924 3,010 37,011

2036 18,257 18,257 16,382 3,213 37,851

2037 18,444 18,444 16,824 3,408 38,675

2038 18,595 18,595 17,249 3,592 39,436

2039 18,718 18,718 17,656 3,767 40,141

2040 18,841 18,841 18,046 3,931 40,817

2041 18,973 18,973 18,371 4,008 41,352

2042 19,150 19,150 18,668 4,080 41,898

2043 19,303 19,303 18,921 4,151 42,375

2044 19,458 19,458 19,156 4,217 42,830

2045 19,613 19,613 19,374 4,278 43,265

2046 19,770 19,770 19,566 4,315 43,651

2047 19,928 19,928 19,756 4,351 44,035

2048 20,088 20,088 19,944 4,383 44,415

2049 20,249 20,249 20,132 4,415 44,795

2050 20,411 20,411 20,318 4,447 45,175

*

ICF projected emissions of HFO-1234yf using special scenarios designed specifically for this analysis and run on 

the U.S. EPA Vintaging Model, Version VM IO file v4.4_12-16-09.