Global emissions of refrigerants HCFC-22 and HFC-134a: unforeseen seasonal contributions

Abstract

HCFC-22 (CHClF2) and HFC-134a (CH2FCF3) are two major gases currently used worldwide in domestic and commercial refrigeration and air conditioning. HCFC-22 contributes to stratospheric ozone depletion, and both species are potent greenhouse gases. In this work, we study in situ observations of HCFC-22 and HFC-134a taken from research aircraft over the Pacific Ocean in a 3-y span [HIaper-Pole-to-Pole Observations (HIPPO) 2009-2011] and combine these data with long-term ground observations from global surface sites [National Oceanic and Atmospheric Administration (NOAA) and Advanced Global Atmospheric Gases Experiment (AGAGE) networks]. We find the global annual emissions of HCFC-22 and HFC-134a have increased substantially over the past two decades. Emissions of HFC-134a are consistently higher compared with the United Nations Framework Convention on Climate Change (UNFCCC) inventory since 2000, by 60% more in recent years (2009-2012). Apart from these decadal emission constraints, we also quantify recent seasonal emission patterns showing that summertime emissions of HCFC-22 and HFC-134a are two to three times higher than wintertime emissions. This unforeseen large seasonal variation indicates that unaccounted mechanisms controlling refrigerant gas emissions are missing in the existing inventory estimates. Possible mechanisms enhancing refrigerant losses in summer are (i) higher vapor pressure in the sealed compartment of the system at summer high temperatures and (ii) more frequent use and service of refrigerators and air conditioners in summer months. Our results suggest that engineering (e.g., better temperature/vibration-resistant system sealing and new system design of more compact/efficient components) and regulatory (e.g., reinforcing system service regulations) steps to improve containment of these gases from working devices could effectively reduce their release to the atmosphere.

Keywords: HCFC-22; HFC-134a; emission seasonality; global emissions; refrigerants.

Fig. 1.

Curtain plots of observed HCFC-22 (Top Row) and HFC-134a (Bottom Row) mixing ratios during HIPPO-3 northbound flights (Left Column), and simulated by ACTM (Right Column, using scaled United Nations inventories). HIPPO flight track and NWAS flask sampling locations are indicated as white lines and cross symbols separately.

Fig. 2.

Optimized global total emissions of HCFC-22, HFC-134a, and CFC-12 based on global surface monitoring site observations and ACTM simulations. Our results are compared with earlier studies derived from similar observations (11, 18, 34, 35) or inventories (UNFCCC) (4).

Fig. 3.

(A) Observed and simulated seasonal cycles of HCFC-22, HFC-134a, SF₆, and CH₃CCl₃ mixing ratios averaged over the period of 1996–2012, at two selected surface sites, namely, Barrow, Alaska (71.2°N, 156.6°W, NOAA) and Mace Head, Ireland (53.3°N, 9.9°W, AGAGE). See Fig. S6 for more sites. Both observations (symbols) and model simulations (lines) are subtracted by their corresponding 12-mo moving averages. The detrended signals are further normalized by the corresponding annual mean mixing ratio (y axis presented in percentage). The error bars show 1 SD of the interannual variability at each month. ACTM simulations use the scaled United Nations inventories (red; UNEP derived for HCFC-22 and CH₃CCl₃ and UNFCCC for HFC-134a) and other available inventories (green; GEIA for HCFC-22, EDGAR4.2 for SF₆, and TransCom-CH₄ for CH₃CCl₃); emissions from these inventories are constant throughout the year. (B) Same as A for HCFC-22 and HFC-134a but over the HIPPO period of 2009–2011. In addition, ACTM simulations use two more emission scenarios: scaled UN inventory with seasonal adjustments (blue) and scaled UN inventory with both seasonal and spatial adjustments (purple).

Fig. 4.

Tropospheric mean mixing ratios of HCFC-22, HFC-134a, SF₆, and CH₃CCl₃ from HIPPO mission 3 in winter and mission 5 in summer (symbols; weighted by pressure for every 10° latitudinal bin) and corresponding forward ACTM simulations using scaled inventory emissions (lines). Both observation and simulation data have been adjusted by subtracting by the global average mixing ratios from corresponding HIPPO observations (indicated in each plot). See Fig. S8 for the complete five HIPPO missions.

Fig. 5.

Latitudinal emissions of HFC-134a (Top) and HCFC-22 (Bottom) from inventories (blue) and derived from inversions of HIPPO data (red) for boreal winter (Left) and summer (Right). Results are median values from 10,000 inversion sensitivity runs; error bars are the 16th and 84th percentiles. The prior emissions (i.e., emission inventories) are much farther from the best estimate of the fluxes in HIPPO-3 inversion than in HIPPO-5 and the emission rates are smaller, causing larger uncertainties in the final estimates.