Changes in HCFC emissions from foam sector in eastern China from 2000-2019

Hydrochlorofluorocarbons (HCFCs) are greenhouse gases and ozone-depleting substances, and existing HCFC emission studies lack a comprehensive study of multiple HCFCs in a single consumption sector. China is a large producer and consumer of HCFCs. The HCFC bank in foam sector in 2019 accounted for 91.3% of the national total, and foam sector was also the second largest source of HCFC emissions. Therefore, the estimation of HCFC emissions and banks for the foam sector is quite important. In this study, the multiple HCFC emission inventory for foam sector in eastern China from 2000 to 2019 was first established by using the bottom-up method. The results showed that the HCFC emissions and bank were 14.9 kt and 453.5 kt in 2019. HCFC-141b used in the polyurethane (PU) foam sector had the largest annual emissions, cumulative emissions, and bank due to its high consumption. The total emissions of HCFC-22 and HCFC-142b used in the extruded polystyrene (XPS) foam sector were similar to those of HCFC-141b. The HCFC emissions from the foam sector were mainly distributed among the three provinces of Jiangsu, Zhejiang, and Shandong. The cumulative GWP- and ODP-weighted emissions of HCFCs were 240.6 Mt CO2-eq and 14.3 kt CFC-11-eq, respectively. The results showed that in order to response to climate change or ozone depletion, we should prioritize the emission reduction of HCFC-22 and XPS foam sector, or HCFC-141b and PU foam sector.


Introduction
HCFCs (Hydrochlorofluorocarbons) are a class of synthetic chemicals mainly used for refrigeration, air conditioning, foam blowing, and solvent agent (Fang et al 2018).As the transitional substitutes of CFCs (Chlorofluorocarbons), the global concentrations and the total chlorine concentrations from HCFCs are increasing year by year (Rigby et al 2017).HCFCs are not only greenhouse gases, but also ozone-depleting substances (ODSs) controlled by the Montreal Protocol (MP) (Flerlage et al 2021, UNEP 2022a, 2022b).Because of the double environmental impact of HCFCs, and its emissions have been widely concerned.
Both top-down and bottom-up methods can be used to estimate HCFC emissions.The top-down method can be used to estimate the total HCFC emissions, but it was difficult to analyze the characteristics and contribution of HCFC emissions from different sectors.For example, Western et al (2022) used a 12-box model to estimate the global HCFC-141b emissions increased from 2017 to 2021 and only evaluated the possible drivers behind this renewed rise in emissions.Vollmer et al (2009) used a FLEXPART model to estimate China's HCFC-22 and HCFC-142b emissions and found HCFC-22 and HCFC-142b emissions amounted to nearly 45% and 30% of the global emissions for 2007 due to a rapidly growing of production and consumption.What's more, O' Doherty et al (2004) and Montzka et al (2014) also estimated the total HCFC (HCFC-141b,  emissions of global by using the 12-box and 3-box models, respectively.Using a bottom-up method, the emission characteristics of one or more HCFCs in different sectors can be estimated.For example, Li et al (2016) and Wu et al (2021) estimated HCFC-22 emissions based on the production and consumption data and analyzed the contribution of HCFC-22 in different sectors.Han et al (2014) and Wang et al (2015) estimated the HCFC-142b, and HCFC-141b emissions from different consumption sectors and found HCFC-142b emissions have steadily increased since 2000, reaching a maximum in 2012 (14.4 kt), due to increased demand for HCFC-142b in different consumption sectors under MP controlled during this period, and the trend of HCFC-141b emissions were similar with that of HCFC-142b and both of them started to increase in 2000 and reaching a maximum in 2012 (16.4 kt).There were some differences between top-down and bottom-up results.For example, Western et al (2022) found that the top-down estimates from 2015-2020 based on HYSPPLIT inversion model were 10%-40% smaller than bottom-up estimates because the disposal emissions estimated may be occurred in polyurethane foam sector.Yi et al (2021) estimated the HCFC-141b and HCFC-142b emissions using interspecies correlation method and found that HCFC-141b emissions were slightly lower than those of the bottom-up inventories of Fang et al (2018) since 2015.The differences were possibly due to the prediction of production and consumption were higher than actual values after 2015.In addition, the existing bottom-up results still lack a comprehensive study of the emission characteristics of multiple HCFCs in a single sector.
China is one of the major producers and consumers of HCFCs.In 2019, China's HCFC production and consumption accounted for 86.7% and 60.3% of the global Ozone Depletion Potential (ODP)-weighted total (UNEP, 2022a, 2022b), respectively.In recent years, studies on HCFC emissions have also focused mainly in China.Some studies have estimated the total HCFC emissions in China (Wan et al 2009, Stohl et (Shao et al 2011, Zhang et al 2014, Wu et al 2014), but these studies also lacked comprehensive studies on multiple HCFCs emission characteristics for a single sector.In 2019, the HCFC bank of China's foam sector reached 1098.5 kt, accounting for 91.3% of the total HCFC bank in China, which was much higher than the second-ranked refrigeration sector (104.4 kt) (Wu et al 2023).Studying the bank of various HCFCs in the foam sector is crucial to accurately estimate its future emission changes.In addition, the foam sector is the second largest HCFC emission sector, and its cumulative HCFC emission reached 354.2 kt from 2000 to 2019, second only to the refrigeration and air conditioning sector ranked first (Wu et al 2023).Although the national HCFCs emissions from China have been estimated (Wu et al 2021), more in-depth, more detailed and more systematic analysis should be further made on the HCFC emission of foam sector in China, such as the comparative analysis of different blowing agents, different consumption sectors and subsectors, and different provinces.
Besides, HCFC emission studies on city, provincial and regional levels are relatively lacking.Eastern China is one of the most economically developed regions in China, with its GDP accounting for 43.6% of the country's total in 2019 (http://www.stats.gov.cn/) and the HCFCs emissions from foam sector in this region contributed 54.2% of the totals in China's foam sector (Wu et al 2023).Therefore, we chose Eastern China as the case study.By collecting the provincial activity level data, the HCFC emission inventory of the foam sector in Eastern China were developed.What's more, the HCFC emission characteristics of different blowing agents (HCFC-22, HCFC-141b and HCFC-142b), different consumer sectors (XPS foam, PU foam and its sub-sectors) and different provinces (covering 9 provinces), as well as their environmental impact were further analyzed, in order to provide scientific basis and reference for the relevant departments in this region and other provinces to formulate effective HCFC emission reduction strategies for foam industries.

Emission estimations
In this study, we identified the main emission sectors of HCFCs in eastern China are polyurethane (PU) foam and XPS foam, among which HCFC-141b is mainly used in PU foam (Wang et al 2015), and HCFC-142b and HCFC-22 are mainly used in XPS foam (Saikawa et al 2014, Simmonds et al 2017).For the foam sector, HCFCs are emitted into the atmosphere in three stages: 1) the foaming stage used as the foaming agent; 2) the usage stage emitted by the leakage of HCFCs; 3) the disposal stage emitted through the landfill.The HCFC emission estimation method in foam sector is from the IPCC Guidelines for National Greenhouse Gas Inventories (IPCC) (IPCC 2006).Emission factors of PU and XPS foam are from Han et al (2014) and Wang et al (2015).The method of estimating emissions is as follows:

Uncertainty analysis
To quantify uncertainties of the emission estimates, we conducted Monte Carlo simulations.In the simulations, activity data and emission factors were randomly varied, following a lognormal distribution.We performed 1,000,000 Monte Carlo runs to ensure robustness.For uncertainties, Han et al (2014) and Wang et al (2015) used uncertainties value (5%, 10%) of HCFC-141b and HCFC-142b for activity data and emission factor, respectively, based on the IPCC guidelines and existing research.Wu et al (2021) assumed an uncertainty of 10% for activity data, emission factors, and related calculation parameters of HCFC-22.In this study, we referred to these literature values and assumed uncertainties of 10% for all three HCFCs, encompassing activity data, emission factors, and related calculation parameters.The overall uncertainty of HCFC emissions was then determined by summing the uncertainties of HCFC-141b, HCFC-142b, and HCFC-22 emissions, respectively.The uncertainty range of HCFC emissions was expressed within the 10th to 90th confidence intervals.

Temporal variation of HCFC emissions
The HCFC emission in 2000 was very low (0.4 kt), increased to 12.8 kt in 2012 and then declined.Since 2015, the HCFC emissions have increased again, reaching 14.9 kt in 2019.The banks of HCFCs increased year by year, from nearly 0 kt in 2000 to 453.5 kt in 2019.As shown in figure 1(a), the annual HCFC-141b emissions have always been the highest.Consequently, the cumulative emissions of HCFC-141b were also the largest, amounting to 82.4 kt between 2000 and 2019, representing 48.0% of the total cumulative emissions of HCFCs (171.7 kt), followed by HCFC-22 (60.5 kt, 35.3%) and HCFC-142b (28.8 kt, 16.8%).In addition, the bank of HCFC-141b also ranked first, with 247.2 kt or 54. % of the total bank in 2019, significantly higher than that of HCFC-22 (31.3%) and HCFC-142b (14.1%).HCFC-141b had the largest annual emissions, cumulative emissions, and banks.This could be due to the high consumption of HCFC-141b, which was significantly higher in annual consumption (2.1 to 29.5 kt) and cumulative consumption (324.5 kt) than HCFC-142b (0.2 to 0.4 kt, 92.9 kt) and HCFC-22 (0.2 to 19.1 kt, 2020.7 kt).These values showed that if we can accelerate the phase-out of HCFC-141b consumption, it will contribute to a significant reduction of HCFC emissions in the foam sector.
As shown in figure 1(b), the emissions of HCFCs were mainly from the initial stage, which started to increase in 2000 and reached a peak of 10.3 kt in 2011 and fell to 6.4 kt in 2019, and the cumulative emissions were 118.9 kt, accounting for 69.2% of the total cumulative emissions of HCFCs at all stages, followed by the use stage, whose emissions increased year by year from 2000 to 2019, with a cumulative emission of 43.2 kt (25.2%).The cumulative HCFC emissions at the disposal stage were the lowest, accounting for only 5.6% of the total cumulative emissions.This was mainly due to the long service life of PU foam (15 to 50 years) and XPS foam (30 years).From 2015 onwards, as the products in the refrigeration insulation and water heater insulation subsectors of PU foam gradually reached the end of their service life (15 years), disposal emissions began n to occur.The average growth rate of disposal emissions from 2015 to 2019 was 305.6%, reaching 3.1 kt in 2019.The 4-year cumulative emissions amounted to 9.6 kt, which was equivalent to 64.4% of the total HCFC emissions in the foam sector in 2019.It was noted that while the proportion of disposal emissions in 2019 was still low, as the other sub-sectors for PU foam and XPS foam products gradually reached the end of their service life, more disposal emissions would be generated in the future.According to the report of the Intergovernmental Panel on Climate Change (IPCC), the waste management of foam products was a key issue in reducing HCFC emissions.Therefore, the establishment and improvement of recovery systems in the foam sector in the future will contribute to the reduction of HCFC emissions.
Existing top-down studies only estimated the national HCFC emissions in China.For comparison with other studies, we calculated the proportion of HCFC estimated in this study to the total HCFC emissions in China estimated by Fang et al (2019) using a top-down method.The results showed that the proportion was stable between 6.0%~8.1%,among which the largest proportion was HCFC-141b, between 23.6% and 45.3% from 2000-2019, suggesting that the HCFC-141b emissions from this region made a great contribution to the foam sector in China.

Spatial distribution characteristics of HCFC emissions
For different provinces in eastern China during 2000-2019 (figures 2(a) and (b)), the HCFC emissions were unevenly distributed in each province, and Jiangsu had the highest cumulative emissions of 47.9 kt, followed by Zhejiang and Shandong, and the cumulative emissions were 43.1 kt and 23.8 kt, respectively.The cumulative emissions of the three provinces accounted for 66.8% of the total HCFC cumulative emissions in eastern China.Emissions from Hebei, Liaoning, and Anhui were similar, and the cumulative emissions were 13.3 kt, 11.8 kt, and 13.0 kt, accounting for 7.8%, 6.8% and 7.6%, respectively.The cumulative emissions of Beijing and Shanghai were 8.2 kt and 7.3 kt, and both of them accounted for 9.0%.Tianjin had the lowest cumulative emissions at 3.0 kt, accounting for only 1.9%.
The spatial distribution of HCFC-141b, HCFC-142b, and HCFC-22 in each province in the foam sectors was consistent, in the order of Jiangsu > Zhejiang > Shandong.For the XPS foam sector, Jiangsu, Zhejiang, and Shandong had the highest emissions of HCFC-142b and HCFC-22 (figure 2(b)).The reason might be that XPS foam was mainly used in the internal and external wall insulation of housing construction, which was closely related to the floor space of buildings constructed of the house.The percentages of floor space of buildings constructed in the three provinces were higher than the other provinces, which together accounted for 70.4% of the region's total, resulting in the cumulative HCFC-142b and HCFC-22 emissions in the three provinces accounted for 71.7% and 72.3% of the totals in eastern China, respectively.However, for the PU foam sector, the spatial and temporal distribution of HCFC-141b emissions in the different sub-sectors was characterized differently across provinces.For example, for the refrigeration insulation sub-sector, Shandong, Jiangsu, and Hebei had higher HCFC-141b emissions, possibly because Refrigerator ownership in the three provinces accounted for 21.5%, 16.3%, and 13.7% of the regional total, respectively.In the spray sub-sector, foaming agents were mainly used as insulation materials and were sprayed on the internal and external walls of houses, also concerning the floor space of buildings constructed.As a result, the spatial distribution characteristics of the provinces were similar to those of the XPS sector, with higher HCFC-141b emissions in Jiangsu, Zhejiang, and Shandong.In addition, for the vehicle polyurethane sub-sector, Jiangsu, Shandong, and Zhejiang had higher emissions of HCFC-141b, which may be due to the higher civilian vehicle ownership in Jiangsu, Shandong and Zhejiang, accounting for 17.2%, 20.8%, and 14.8% of the regional totals, respectively.
For the different stage analyses in eastern China during 2000-2019 (figure 2(c)), HCFC emissions from the initial and usage stages had the same distribution characteristics.Jiangsu, Zhejiang, and Shandong had the largest cumulative emissions, and the cumulative emissions from the initial stage of these three provinces were 35.0 kt, 31.8 kt, and 15.1 kt, accounting for 29.4%, 26.7%, and 12.7% of total HCFC emissions in the initial stage.The cumulative emissions from the usage stage of these three provinces were 11.3 kt, 10.1 kt, and 6.4 kt, accounting for 26.3%, 23.5%, and 14.8%, respectively.However, the distribution characteristics of the disposal stage were different from those of the initial and usage stages.The provinces with the highest cumulative emissions from the disposal stage were Shandong, Jiangsu, Hebei, and Zhejiang ranked fourth, and the total cumulative emissions of the four provinces were 6.4 kt, accounting for 64.1% of the total HCFC emissions for the disposal stage.

Double environmental impact
Considering that HCFCs are both greenhouse gases and ozone-depleting substances, it is necessary to quantify the environmental impact by estimating their GWP-weighted emissions and ODP-weighted emissions.GWPweighted emissions and ODP-weighted emissions are calculated by multiplying the 100-year Global Warming Potential (GWP) and Ozone Depletion Potential (ODP) value of each HCFCs.As shown in figures 3(a) and (b), the results showed that both GWP-weighted emission and ODP-weighted emission increased from 2000 at 0.6 Mt yr −1 and 0.1 kt, respectively.By 2019, GWP-weighted emissions and ODP-weighted emissions had increased to 19.1 Mt yr −1 and 1.3 kt, respectively.
From 2000 to 2019, the cumulative emissions of GWP-weighted and ODP-weighted were 240.6 Mt CO 2 -eq and 14.3 kt CFC-11-eq, respectively.Although HCFC-22 had the lowest cumulative emissions, its GWP value was much higher than HCFC-141b and HCFC-142b, so it became the main greenhouse gas, with the GWPweighted cumulative emissions 109.6 Mt CO 2 -eq (45.6%), followed by HCFC-142b and HCFC-141b with 64.2 Mt CO 2 -eq (16.8%) and 66.6 Mt CO 2 -eq (27.7%), respectively.HCFC-141b had the largest ODP-weighted cumulative emissions because of its largest emission and the highest ODP value, with the ODP-weighted cumulative emissions of 9.1 kt CFC-11-eq (63.5%), followed by the HCFC-22 and HCFC-142b with 3.3 kt CFC-11-eq (23.3%) and 1.9 kt CFC-11-eq (13.1%), respectively.Above all, HCFC-22 and HCFC-141b were the biggest contributions to GWP-weighted and ODP-weighted emissions among the HCFCs for foam sector in eastern China.The GWP-weighted and ODP-weighted emissions were different for different foam sectors.The XPS foam sector had the highest GWP-weighted emissions, with cumulative emissions of 176.2 Mt CO 2 -eq from 2000-2019.There are two possible reasons for this: 1) the total emissions of HCFCs in XPS foam were 89.4 kt, higher than HCFC-141b (82.4 kt);2) the GWP values of HCFC-22 (1810) and HCFC-142b (2310) were higher than that of HCFC-141b (782).However, PU foams had the highest ODP-weighted emissions, with cumulative emissions of 9.1 kt CFC -11 -eq, and the main contributors in the PU foam sector were vehicles polyurethanes (25.5%), refrigeration insulation (23.6%) and sheet (18.0%).The results showed that if we want to combat climate change, priority should be given to HCFC emission reductions in the XPS foam sector.To protect the ozone layer, priority should be given to the PU foam sector.To coordinate climate change and protect the ozone layer, effective emission reductions in both two foam sectors simultaneously are essential.
The distribution characteristics of ODP and GWP-weighted emissions by province were relatively consistent, mainly in Jiangsu, Zhejiang, and Shandong provinces (figures 4(a) and (b)).The ODP and GWPweighted emissions of these three provinces were 3.8 kt CFC-11-eq, 3.4 kt CFC-11-eq, 2.1 kt CFC-11-eq, and

Figure 1 .
Figure 1.HCFC annual emissions of foam sector from 2000-2019 in foam sector.(a) HCFC emissions from different HCFC species; (b) HCFC emissions from different stages; The embedded small figure presented the HCFC emissions from disposal stage and its average growth rate during 2015-2019.

Figure 2 .
Figure 2. The annual and cumulative HCFC emissions during 2000-2019.(a) The annual emissions by each province; (b) Cumulative emissions and 2019 emission for different provinces; (c) The cumulative emissions of each substance; (d) The cumulative emissions for each stage.

Figure 3 .
Figure 3. GWP-weighted and ODP-weighted emissions in Eastern China from foam sector for HCFC-141b, HCFC-142b, HCFC-22 and their percentage to the regional totals during 2000-2019.(a) GWP-weighted emissions of each substance; (b) ODP-weighted emission of each substance.

Figure 4 .
Figure 4. GWP-weighted and ODP-weighted emissions in Eastern China from foam sector and their distribution characteristics (a) GWP-weighted emissions of each province; (b) ODP-weighted emission of each province.
al 2010, Kim et al 2010, Lunt et al 2018, Fang et al 2019, Yao et al 2019, Yi et al 2021, Wu et al 2023), eastern China (Western et al 2022) or Pearl River Delta (PRD) The values of the emission factor for PU foam sector are provided in Support Information (SI) tableS1.EF , , is the total HCFC emissions (kt) from the foam sector in year t, E t PU , is the HCFC emissions (kt) from the PU foam sector in year t, E t XPS , is the HCFC emissions (kt) from the XPS foam sector in year t; EF , , and EF PU dis , are the emission factor of PU foam sector from the foaming process (%), usage process (%) and disposal process (%), respectively.