Abstract: We report a 40-year history of SF₆ atmospheric mole fractions measured at the Advanced Global Atmospheric Gases Experiment (AGAGE) monitoring sites, combined with archived air samples, to determine emission estimates from 1978 to 2018. Previously we reported a global emission rate of 7.3±0.6 Gg yr⁻¹ in 2008 and over the past decade emissions have continued to increase by about 24 % to 9.04±0.35 Gg yr⁻¹ in 2018. We show that changing patterns in SF₆ consumption from developed (Kyoto Protocol Annex-1) to developing countries (non-Annex-1) and the rapid global expansion of the electric power industry, mainly in Asia, have increased the demand for SF₆-insulated switchgear, circuit breakers, and transformers. The large bank of SF₆ sequestered in this electrical equipment provides a substantial source of emissions from maintenance, replacement, and continuous leakage. Other emissive sources of SF₆ occur from the magnesium, aluminium, and electronics industries as well as more minor industrial applications. More recently, reported emissions, including those from electrical equipment and metal industries, primarily in the Annex-1 countries, have declined steadily through substitution of alternative blanketing gases and technological improvements in less emissive equipment and more efficient industrial practices. Nevertheless, there are still demands for SF₆ in Annex-1 countries due to economic growth, as well as continuing emissions from older equipment and additional emissions from newly installed SF₆-insulated electrical equipment, although at low emission rates. In addition, in the non-Annex-1 countries, SF₆ emissions have increased due to an expansion in the growth of the electrical power, metal, and electronics industries to support their continuing development.

There is an annual difference of 2.5–5 Gg yr⁻¹ (1990–2018) between our modelled top-down emissions and the UNFCCC-reported bottom-up emissions (United Nations Framework Convention on Climate Change), which we attempt to reconcile through analysis of the potential contribution of emissions from the various industrial applications which use SF₆. We also investigate regional emissions in East Asia (China, S. Korea) and western Europe and their respective contributions to the global atmospheric SF₆ inventory. On an average annual basis, our estimated emissions from the whole of China are approximately 10 times greater than emissions from western Europe. In 2018, our modelled Chinese and western European emissions accounted for ∼36 % and 3.1 %, respectively, of our global SF₆ emissions estimate.