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## Preliminary report : Analyses of t CFP ’s potential impact on atmospheric ozone
Dong Wang, Seth Olsen, and Donald Wuebbles Department of Atmospheric Sciences University of Illinois, Urbana, IL 61801

Abstract

Trans

- 1

- chloro

- 3,3,3

- trifluoropropylene (tCFP
, CHCl=CHCF 3 ) is a chemical compound proposed to substitute for currently used blowing agents due to tCFP possess ing advantage s for fire safety , air quality, and climate properties. As a molecule containing a chlorine atom, tCFP might be of concern because o f its potential to affect the amount of ozone in the global atmosphere. This study uses a state

- of

- the

- art 3

- D global atmosphere chemistry

- climate model to evaluate such potential impact s

. Our analyses indicate that that there is statistically zero (less than 0.01%) impact on global atmospheric (tropospheric and stratospheric) ozone abundance if tCFP were substituted for all compound s it might replace and assuming all of the tCFP used is released in to the atmosphere. We also found that a tCFP source strength of 21.72Tg/ y r would be necessary to result in a decrease of annual ly

- averaged global atmospheric ozone of 0.1% , a small but statistically significant impact

. We also derived that the ODP of tCFP is 0.0 0 024 assuming emissions occurring in the major parts of the world that are heavy users of the blowing agents tCFP might replace.


### Introduction

Trans

- 1

- chloro

- 3,3,3

- trifluoropropylene (tCFP, chemical formula CHCl=CHCF 3 ) has been p roposed as a potential substitute compound for currently used blowing agents with potential climate issues (the hydrofluorocarbons (HFCs) HFC

- 254a,

- 365mfc,

- 134a,

- 227ea and the h ydrochlorofluorocarbons (HCFCs) HCFC

- 141b,

- 142b,

- 22 ) or with flammability and air quality concerns ( the hyd rocarbons (HC) c

- Pentane, n

- Pentane). However, tCFP contains chlorine, and possible stratospheric ozone loss from its release of chlorine to the atmosphere is of

concern. We carry out this study in order to assess tCFP’s impact on ozone in the atmosphere

w ith a state

- of

- the

- art numerical model that simulates the chemistry and physics of the atmosphere. In particular, we are interested in how much the impact on atmospheric ozone would be if all blowing agents were substituted by tCFP and all tCFP used were r eleased into the atmosphere. In addition, we are interested in how much tCFP would be necessary to result in 0.1% loss in global ozone. We develop two emission case s to address these two questions. This is a brief report of our preliminary findings.2



### Model description

For th is study, we use the Whole Atmosphere Community Climate Model (WACCM) version 3.5.48 , an atmosphere chemistry

- climate model developed by the Nationa l Center for Atmospheric Research (NCAR)

. The model has been evaluated and used in a number of scientific studies, for example, in the Stratospheric Processes and their Role in Climate (SPARC) 2010 Report (Eyring et al., 2010)

. WACCM 3.5.48 numerically simulates the atmosphere from the surface up to 4.5 × 10 - 4 Pa ( ~145km ) . The horizon tal resolu tion is 2.5° longitude ×1.9° latitude. The model is run in offline mode, which means that the meteorological fields are provided by a previous run of WACCM 3.5 represe nting the year 2000 atmosphere ( Garc ia, private communication, 2007)

. The model simulates 125 chemical species and uses the JPL06 recommendations (Sander et al., 2006) including extension s for non

- methane hydrocarbon chemistry
, which is key to good represent ation of tropospheric oxidative capacity. The model has good performance in simulating the stratosphere and the upper troposphere and lower stratosphere as shown in e.g., the Chemistry

- Climate Mode l Validation Activity (CCMVal) ( Eyring et al., 2010; Gettelman et al., 2010)

. The tCFP decomposition in the atmosphere is primarily initiated by its reaction with hydroxyl radical (OH) in the troposphere. Here we adopt the most recent estimate of the reaction rate of 4.4 × 10 - 13 cm 3 molec - 1 s - 1 (Anderson et al., 2008) , assuming no temperature dependence

. 

### The Modeling Studies

T wo different types of analyses are done in this study towards understanding the potential effects of tCFP on ozone

. The first case , P erturbation 1
, is designed to determine the maximum impact tCFP emissions , assuming tCFP use as a blowing agent, could possibly have on atmospheric

ozone

. W e assume in this scenario the currently used blowing agent s , as listed for different regions in Table 1 (Rajiv Singh, private communication, 2011)
, are completely substituted by tCFP

. The estimated release rate into t he atmosphere is around 20 %; however, here we assume that 100% of the tCFP used is released into the atmosphere , to study the maximum possible impact

. Thus a global tCFP emission rate of 0.171 Tg/yr is derived. Based on the data in Table 1
, w e calculate tCFP emissions for European Union, Japan, China, India, Turkey, Middle East and North Africa, Latin America and North America, assuming that within each region tCFP is uniformly emitted both spatially and temporally

. Figure 1 depicts tCFP emissions distribution in perturbation 1 scenario

. The second case , P erturbation 2
, examines how much tCFP would cause a 0.1% loss in global column ozone

. A previous st udy by Patten and Wuebbles (2010 ) found that a 50.0 Tg/yr tCFP emission resulted in 0.321% decrease in global column ozone. Thus i n the second scenario we

assume globally 15.57 Tg tCFP is emitted into the atmosphere per year. The geographic pattern of this emission is the same as that in Figure 1, except that the emission rate is 91 times larger than that in Figure 1. It is expected to cause nearly 0.1% loss in total atmospheric ozone in this3

scenario

. In this study the model result can be differe nt from being exactly 0.1% loss. I n this
case, we can scale the emission so as to achieve 0.1% ozone loss

. This is justified because previous studies have shown that within this still small magnitude of perturbation ozone changes linearly with emissions

. In addition to the two tCFP perturbation scenarios, we run a reference scenario which is identical to the perturbation scenarios except that no tCFP is emitted. The emissions and lower boundary concentrations of the major source gases correspond to year 20 04 background atmosphere. NO x source from lightning is 5.0 TgN, according to Schumann and Huntrieser (2007). The model set

up is described in Patten et al. (2011).


### Result s

To ensure that the model is run to chemical steady state, we carry out seven years of simulation for each of the above stated scenarios. The year

- to

- year variation is less than 0.02% for ozone and less than 0.03% for tCFP. Only the seventh year’s result is shown here.

The s teady state glob al atmospheric burdens of tCFP derived for the two scenarios are 0.0 14 and 1.313 Tg ( Table 2 ) for Perturbation s 1 and 2, respectively. These correspond to the assumed tCFP emissions of 0.171 and 15.57 Tg/yr
, respectively. Based on these simulations , the fi rst

order estimate of tCFP’s lifetime is ~29.9 and ~30.8 days based on the first and second perturbation scenario s, respectively

. These are lower than the ~ 40 day lifetime estimate of Patten and Wuebbles (2010). The difference may arise both from difference s in the assumed emission distribution and from this study using an updated version of the atmospheric model

. Simulated tCFP mixing ratios are highest near the surface in the Northern Hemisphere and decrease quickly with altitude
, with extremel y little tCFP reaching the Southern H emisphere (Figures 2 and 3). Peak zonal mean mixing ratios are ~ 3.4 ppt for the Perturbation 1 scenario, the maximum possible real world emissions. In P erturbation 2
, peak mixing ratios are as high as 400 pptv. These f

eatures, mixing ratio decreases with altitude and decreases southward
, are to be expected given tCFP’s short lifetime and its predominant emissions in the Northern H emisphere.
In the first perturbation scenario the Cl y (= Cl + 2×Cl + ClO + OClO + 2×Cl 2 O 2 + HCl + HOCl + ClONO 2 + BrCl) mixing ratio increased by no more than 10% in the troposphere, with more increase in the lower troposphere at northern mid

- and high

- latitudes (Figure 4 ). In the second perturbation scenario, the Cl y mixing ratio increases to more than 6 times of that in the reference atmosphere in the lower northern troposphere (Figure 5 ).
Figures 6 and 7 show the relative change (%) of annual, zonal mean ozone mixing ratios in the perturbation cases compared with those in the referenc e scen ario. As shown in Figure 6 , there is no systematic shift of ozone mixing ratios in the perturbation 1 scenario. These emissions result in a 0.0073% change in global ozone burden (Table 3). Changes of this magnitude are not4

statistically significant from th e model variability, and thus are not statistically different from

zero.

In Perturbation scenario 2
, with the 15.57 Tg tCFP emission (designed specifically to achieve a statistically significant change)
, there is 0.072% total atmospheric ozone loss much o f which occurs in the troposphere. As shown in Figure 6, there is 0.2%~0.8% ozone loss in troposphere in the northern hemisphere, with largest relative loss at high

- latitudes. Overall tropospheric ozone decreases by 0.29%. Scaling this result we estimate t hat a 21.72 Tg p er year tCFP emission would lead to a 0.1% loss in global ozone. Thus, in order for tCFP to have cause d an ozone loss of 0.1% it would need to be emitted at a rate nearly two orders of magnitude greater than the worst case real world estima tes used in Perturbation scenario 1. Also from this simulation we calculate the ODP of tCFP using an approach akin to that used in Patten and Wuebbles (2010). The derived ODP for this assumed distribution of emissions was found to be 0.00024. Although this is slightly lower than the ODP of 0.00034 determined in Patten and Wuebbles (2010), it is similar in magnitude. As with the difference in lifetime this difference may arise both from differences in the assumed emission distribution and from this study using an updated version of the atmospheric model.


### Conclusions

Ou r modeling study suggest s that the potential impact of tCFP on ozone in the atmosphere is likely to be extremely small , essentially immeasurable . I f currently used blowing agent s were to be entirely replaced by tCFP and all of the tCFP used were released to the atmosphere
, the impact on atmospheric ozone will be statistically zero (less than 0.01% change in total column

ozone )

. T o cause a statistically significant level of 0.1% loss in total column atmospheric ozone, tCFP emission must reach 21.72 Tg/yr, which is nearly 130 times above the current emissions of all blowing agents usage in 2010. The ODP for tCFP using the regional ly assumed emissions in this study is 0.00 0 24 , an extremely small value

.

References:
Andersen, M. P. S., Nilsson, E. J. K., Nielsen, O. J., Johnson, M. S., Hurley, M. D. and Wallington, T. J.: Atmos pheric chemistry of trans

- CF 3 CH =CHCl: Kinetics of the gas

- phase reactions wi th Cl atoms, OH radicals, and O 3 . J. Photochem. Photobiol. A

- Chem ., 199, 92

- 97, 2008.
Eyring, V., T. G. Shepherd, and D. W. Waugh (Eds.) : Stratospheric Processes And Their Role in Climate Report on the Evaluation of Chemistry

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. SPARC Report No. 5, WCRP

- 132, WMO/TD

- No. 1526, accessed at http://www.atmosp.physics.utoronto.ca/SPARC , 2010

.5

Gettelman, A., M. I. Hegglin, S. W. Son, M. Fujiwara, S. Tilmes, L. Pan, P. Hoor, H. Lee, G. L. Manney, T. Birner, G. Stiller, M. Rex, S. Kremser, D. Wuebbles, K. A. Walker, and J. A. Anel : Upper Troposphere and Lower Stratosphere, in Stratospheric Processes And Their Role in Climate Report on the Evaluation of Chemistry

- Climate Models (SPARC CCMVal), edited by V. Eyring, T. G. Shepherd, and D. W. W augh, pp. 253

- 304, World Meteorological Organization, SPARC Report No. 5, WCRP

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- No. 1526, World Climate Research Programme, accessed through http://www.atmosp.physics.utoronto.ca/SPARC , 2010

. Patten, K. O. , V. G. Khamaganov, V. L. Orkin, S. L. Baughcum and D. J. Wuebble s : 2

- Bromo

3,3,3

- Trifluoroprop ene : OH Reaction Rate Constant, IR Absorption Spectrum, Ozone Depletion Potentials and Global Warming Potential, in preparation, 2011

. Patten, K. O. and D. J. Wuebble s : Atmospheric lifetimes and Ozone Depletion Potentials of
trans

- 1

- chloro

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- trifluoropropylene and trans

- 1,2

- dichloroethylene in a three

- dimensional model

. Atmospheric Chemistry and Physics , 10, 10867

- 10874, 2010.
Sander, S. P., R. R. Friedl, D. M. Golden, M. J. Kurylo, G. K. Moo rtgat, H. Keller

- Rudek, P. H. Wine, A. R. Ravishankara, C. E. Kolb, M. J. Molina, B. J. Finlayson

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- 2, NASA Panel for Data Evaluation, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, July 10. Available via http://jpldataeval.jpl.nasa.gov , 2006

. Schumann, U. and H. Huntrieser: The global lightning

- induced nitrogen oxides sourc e, Atmospheric Chemistry and Physics, 7, 3823

- 3907, 2007.6

Table 1. HFC s, HCFCs and hydrocarbons (HC) usage (in Mlbs) as blowing agents in 2010 in major regions of the world that have heavy users of blowing agents (Rajiv Singh, private communication, 2011)

.

EU a Japan China India Turkey MENA b L.A. c N.A. d total total 83.4 15.0 116.2 22

. 0 11.5 22.9 39.9 65.8 376.7

a EU: European Union b MENA: Middle East and North Africa

c L.A.: Latin America d N.A.: North America7

Table 2

. Global tCFP emissio n s (Tg/yr) used in the model
, and the derived atmospheric burdens (Tg) and lifetimes (days) in the two perturbation cases.

global emission (Tg/yr) atmospher ic burden (Tg) l ifetime (days)

P erturbation 1 0.171 0.014 29.9

P erturbation 2 15.57 1.313 30.88

Table 3

. G lobal atmospheric, tropospheric and stratospheric ozone burden s (Tg) derived in the model for the scenarios studied
, and the determined percentage change s in ozone relative to the reference scenario.

global O 3 % change from ref. trop. O 3 % change from ref. strat. O 3 % change from ref.
R eference 3139.86 369.18 2770.68

P erturbation 1 3140.09 + 0.0073 369.20 + 0.0054 2770.88 + 0.0072

P erturbation 2 3137.60

- 0.0717 368.12

- 0.2881 2769.49

- 0.04299

Figure 1. The assumed tCFP emissions (molecules/cm 2 s) in the Perturbation 1 scenario.10

Figure 2

. Annual, zonal mean tCFP mixing ratio (pptv) derived for Perturbation 1, the scenario in which currently used blowing agents have been substituted by tCFP and the used tCFP is completely released to the atmosphere.11

Figure 3

. Annual, zonal mean tCFP mixing ratio (pptv) derived for the 15.57 Tg tCFP per year emission scenario.12

Figure 4

. C hange (%) in annual, zonal mean Cl y mixing ratio derived for Perturbation 1, the scenario in which currently used blowing agents have been substituted by tCFP and the used tCFP is completely released to the atmosphere , relative to the reference scenario

.13

Figure 5

. C hange (%) in annual and zonal mean Cl y mixing ratio derived for the 15.57 Tg tCFP per year emission scenario (Perturbation 2) relative to the reference scenario.14

Figure 6

. C hange (%) in annual, zonal mean ozone mixing ratio derived for Perturbation 1, the scenario in which currently used blowing agents have been substituted by tCFP and the used tCFP is completely released to the atmosphere.15

Figure 7

. Change (%) in annual, zonal mean ozone mixing ratio derived for the 15.57 Tg tCFP per year emission scenario (Perturbation 2) relative to the reference scenario

.