Abstract
Determining the leakage rates of halogenated refrigerants from operating mobile air conditioning systems (MACs) is a challenging task. Here, we take advantage of a heavily trafficked tunnel with a traffic flow of over 40,000 motor vehicles per day in south China. We carried out measurements in 2014 on hot and humid days, and therefore, it is reasonable to assume that essentially all of the MAC units would be turned on to ensure the thermo-comfort of the occupants. Thus, we obtained the leakage rates of the three most important refrigerants from the operating MACs aboard the on-road vehicles. The emission factors (EFs) of HFC-134a, HCFC-22, and CFC-12 from the on-road operating MACs are 1.27 ± 0.11, 0.47 ± 0.04, and 0.17 ± 0.04 mg km–1 veh–1, respectively. Normalized by the percentages of vehicles using different refrigerants in their MACs, the emission rates of HFC-134a, HCFC-22, and CFC-12 are 52.2, 329, and 59.5 mg h–1 veh–1, respectively. This emission rate of HFC-134a is approximately 10 times higher than those previously reported in Europe for stationary conditions and a whole-lifetime average of fugitive losses. The unusually high leakage rates suggest that improving the leak tightness of MACs in China would help to greatly lower their emissions. The global warming potentials associated with refrigerant leakage is equal to 1.4% of the CO2 directly emitted due to fuel consumptions.
Highlights
CFC-12 (CCl2F2), HCFC-22 (CHClF2), and HFC-134a (CH2FCF3) are the most abundant chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), and hydrofluorocarbon (HFC) compounds in the Earth’s atmosphere, respectively
Are the paired average concentrations of refrigerant i measured at the outlet station and inlet station during the same time interval, respectively; Vair (m s−1) is the air velocity parallel to the tunnel measured by the 3-D sonic anemometer; A (m2) is the tunnel cross-section area; N is the total number of vehicles passing through the tunnel during the specified time interval, and L is the length of the tunnel between the outlet and inlet stations
The average mixing ratios of HFC-134a and HCFC-22 at the entrance were 116 ± 20 and 416 ± 32 ppt, respectively. These values are higher than the corresponding values of 84 and 209 ppt measured at the entrance to the Gubrist tunnel in Switzerland in 2002.29 Similar levels of CFC-12 were measured in this study (554 ± 12 ppt) as were observed in the Gubrist tunnel (559 ppt), even though global levels of CFC-12 have declined by approximately 20 ppt since 2002.1 These results indicate a relatively large enhancement over background levels for the Zhujiang tunnel
Summary
CFC-12 (CCl2F2), HCFC-22 (CHClF2), and HFC-134a (CH2FCF3) are the most abundant chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), and hydrofluorocarbon (HFC) compounds in the Earth’s atmosphere, respectively. While regular annual leakage rates are typically estimated based on the difference in mass between the initial and remaining refrigerants over some time interval, and the refrigerant leakage from stationary vehicles can be measured using a Sealed Housing for Evaporative Determination (SHED) apparatus,[28] it is not easy to obtain measurement-based EFs for refrigerant leakage from MACs under on-road operation conditions In this present study, we take advantage of a field campaign that was conducted in June 2014 in the Zhujiang Tunnel (23.11° N, 113.23° E) in urban Guangzhou, south China.[30−32] During this campaign, EFs of CFC-12, HCFC-22, and HFC-134a from the MACs onboard the on-road vehicle fleet were measured. Are the paired average concentrations of refrigerant i measured at the outlet station and inlet station during the same time interval, respectively; Vair (m s−1) is the air velocity parallel to the tunnel measured by the 3-D sonic anemometer; A (m2) is the tunnel cross-section area; N is the total number of vehicles passing through the tunnel during the specified time interval, and L (km) is the length of the tunnel between the outlet and inlet stations
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