Atmospheric HCFC-22, HFC-125, and HFC-152a at Cape Point, South Africa

Estimate Gaps of Montreal Protocol-Regulated Potent Greenhouse Gas HFC-152a Emissions in China Have Been Explained

1,1-Difluoroethane (HFC-152a) is a hydrofluorocarbon regulated by the Montreal Protocol, and its emissions in China are of concern as China will regulate HFC-152a in 2024. However, no observation-inferred top-down estimates were undertaken after 2017, and substantial gaps existed among previous estimates of China's HFC-152a emissions. Using the atmospheric observations and inverse modeling, this study reveals China's HFC-152a emissions of 9.4 ± 1.7 Gg/yr (gigagrams per year), 10.6 ± 1.8 Gg/yr, and 9.7 ± 1.5 Gg/yr in 2018, 2019, and 2020, respectively. In addition, we display an overall increasing trend during 2011-2020, which is in contrast to the decreasing and steady trend reported by the Emission Database for Global Atmospheric Research (EDGAR) and the Chinese government, respectively. Subsequently, we establish a comprehensive bottom-up emission inventory matching with top-down estimates and thus succeed in explaining the gaps among previous estimates. Furthermore, the contribution of China's emissions to global HFC-152a emission growth increased from 15% during 2001-2010 to >100% during 2011-2020. An emission projection based on our improved inventory shows that the Kigali Amendment (KA) would assist in avoiding 1535.6-4710.6 Gg (251.8-772.5 Tg CO2-eq) HFC-152a emissions during 2024-2100. Our findings indicate relatively accurate China's HFC-152a emissions and provide scientific support for addressing climate change and implementing the KA.

Establishment of HCFC-22 National-Provincial-Gridded Emission Inventories in China and the Analysis of Emission Reduction Potential

Due to chlorodifluoromethane's (CHClF₂, HCFC-22) dual environmental impact on climate change and ozone depletion, its emissions have attracted international attention. In this study, a set of national-provincial-gridded (1° × 1°) emission estimation methods were built and applied to obtain the national, provincial, and gridded emission inventories in China in 1990-2019. In addition, the HCFC-22 emission reduction potential of different emission scenarios was analyzed. The results show that China's HCFC-22 emissions reached a peak in 2017 and that the cumulative emissions in 1990-2019 were 1576.8 (1348.2-1819.0) kt (equivalent to 86.7 kt CFC-11 and 2854.1 Mt CO₂). China's HCFC-22 emissions in the east were higher than those in the west, and the emissions in the south were higher than those in the north. Under the control of the Montreal Protocol, China will reduce the cumulative emissions of 17 840.8 kt (avoiding 0.08° of global warming by 2056) in 2020-2056. If the disposal refrigerant can be effectively recycled in the future, the HCFC-22 emission reduction in this period will reach 18 020.3 kt. The established emission estimation methods and obtained results can provide scientific and technological support for ozone layer protection and for addressing climate change.

A review of bottom-up and top-down emission estimates of hydrofluorocarbons (HFCs) in different parts of the world

Hydrofluorocarbons (HFCs) are widespread alternatives for the ozone-depleting substances chlorofluorocarbons and hydrochlorofluorocarbons. They are used mainly as refrigerants or as foam-blowing agents. HFCs do not deplete the ozone layer, but they are very potent greenhouse gases, already contributing to global warming. Since 2019 HFCs are regulated under the Kigali Amendment to the Montreal Protocol, which demands reliable emission estimates to monitor the phase-down. Quantification of emissions is performed with two methods: bottom-up from product inventories or data on chemical sales; or top-down, inferred from atmospheric measurements by inverse modelling or interspecies correlation. Here, we review and compare the two methods and give an overview of HFC emissions from different parts of the world. Emission estimates reported by the different methods vary considerably. HFC emissions of developed countries (Annex I) are reported to the United Nations Framework Convention on Climate Change. These bottom-up estimates add up to only half of global emissions estimated from atmospheric data. Several studies with regional top-down estimates have shown that this gap is not owed to large-scale underreporting of emissions from developed countries, but mostly due to emissions from developing countries (non-Annex I). China accounts for a large fraction of the emissions causing the gap, but not entirely. Bottom-up and top-down estimations of emissions from other developing countries that could identify other large emitters are largely unavailable. Especially South America, West-, Central- and East-Africa, India, the Arabian Peninsula and Northern Australia are not well covered by measurement stations that could provide atmospheric data for top-down estimates.

Emissions and Marine Boundary Layer Concentrations of Unregulated Chlorocarbons Measured at Cape Point, South Africa

Unregulated chlorocarbons, here defined as dichloromethane (CH₂Cl₂), perchloroethene (C₂Cl₄), chloroform (CHCl₃), and methyl chloride (CH₃Cl), are gases not regulated by the Montreal Protocol. While CH₃Cl is the largest contributor of atmospheric chlorine, recent studies have shown that growth in emissions of the less abundant chlorocarbons could pose a significant threat to the recovery of the ozone layer. Despite this, there remain many regions for which no atmospheric monitoring exists, leaving gaps in our understanding of global emissions. Here, we report on a new time series of chlorocarbon measurements from Cape Point, South Africa for 2017, which represent the first published high-frequency measurements of these gases from Africa. For CH₂Cl₂ and C₂Cl₄, the majority of mole fraction enhancements were observed from the north, consistent with anthropogenically modified air from Cape Town, while for CHCl₃ and CH₃Cl, we found evidence for both oceanic and terrestrial sources. Using an inverse method, we estimated emissions for south-western South Africa (SWSA). For each chlorocarbon, SWSA accounted for less than 1% of global emissions. For CH₂Cl₂ and C₂Cl₄, we extrapolated using population statistics and found South African emissions of 8.9 (7.4-10.4) Gg yr^-1 and 0.80 (0.64-1.04) Gg yr^-1, respectively.