Abstract
AbstractThe phase out of anthropogenic ozone‐depleting substances such as chlorofluorocarbons under the terms of the Montreal Protocol led to the development and worldwide use of hydrofluorocarbons (HFCs) in refrigeration, air conditioning, and as blowing agents and propellants. Consequently, over recent years, the atmospheric abundances of HFCs have dramatically increased. HFCs are powerful greenhouse gases and are now controlled under the terms of the 2016 Kigali Amendment to the Montreal Protocol. HFC‐134a is currently the most abundant HFC in the atmosphere, breaking the 100 ppt barrier in 2018, and can be measured in the Earth's atmosphere by the satellite remote‐sensing instrument ACE‐FTS (Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer), which has been measuring since 2004. This work uses the ACE‐FTS v4.0 data product to investigate global distributions and trends of HFC‐134a. These measurements are compared with a simulation of SLIMCAT, a state‐of‐the‐art three‐dimensional chemical transport model, which is constrained by global surface HFC‐134a measurements. The agreement between observation and model is good, although in the tropical troposphere ACE‐FTS measurements are biased low by up to 10–15 ppt. The overall ACE‐FTS global trend of HFC‐134a for the altitude range 5.5–24.5 km and 2004–2018 time period is approximately linear with a value of 4.49 ± 0.02 ppt/year, slightly lower than the corresponding SLIMCAT trend of 4.66 ppt/year. Using a simple box model, we also estimate the annual global emissions and burdens of HFC‐134a from the model data, indicating that emissions of HFC‐134a have increased almost linearly, reaching 236 Gg by 2018.
Highlights
Humanity's love affair with chlorofluorocarbons (CFCs), which began in the middle of the 20th century, was always destined to end in tears
This work uses the Atmospheric Chemistry Experiment-Fourier transform spectrometer (ACE-FTS) v4.0 data product to investigate global distributions and trends of HFC-134a. These measurements are compared with a simulation of SLIMCAT, a state-of-the-art three-dimensional chemical transport model, which is constrained by global surface HFC-134a measurements
One of the most successful environmental treaties ever signed (McKenzie et al, 2019), the Montreal Protocol has reduced the emissions of these ozone-depleting substances (ODSs) under a legal framework, thereby saving millions of people from the ravages of skin cancer (Chipperfield et al, 2015), it will be many years before ozone levels recover to previous levels on account of the long atmospheric lifetimes of ODSs, for example, CFC-12 has an overall atmospheric lifetime of 102 years (WMO/UNEP, 2018)
Summary
Humanity's love affair with chlorofluorocarbons (CFCs), which began in the middle of the 20th century, was always destined to end in tears. The abundance of HFC-134a has grown steadily since the early 1990s (NOAA, 2018), breaking the 100 ppt barrier in 2018 It has a 100-year global warming potential of 1,360 (WMO/UNEP, 2018), and an atmospheric lifetime of 14 years (WMO/UNEP, 2018). The aim of the present work is to understand the HFC-134a global distribution and trends derived from ACE-FTS observations, and use these to validate the HFC-134a mixing ratios output from the SLIMCAT model, a state-of-the-art three-dimensional (3D) chemical transport model (CTM), one of the few to include stratospheric fluorine chemistry. This is the first detailed comparison between satellite observations. The model outputs will be used to derive tropospheric and stratospheric burdens, annual global emissions of HFC-134a over the observation period, and the annual net fluxes of HFC-134a into the stratosphere
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