Emissions of HFC-23 do not reflect commitments made under the Kigali Amendment.

HFC-23 (trifluoromethane) is a potent greenhouse gas released to the atmosphere primarily as a by-product of HCFC-22 (chlorodifluoromethane) synthesis. Since 2020, the Kigali Amendment to the Montreal Protocol has required Parties to destroy their HFC-23 emissions to the extent possible. Here, we present updated HFC-23 emissions estimated from atmospheric observations.

Increases in Global and East Asian Nitrogen Trifluoride (NF) Emissions Inferred from Atmospheric Observations.

Nitrogen trifluoride (NF) is a potent and long-lived greenhouse gas that is widely used in the manufacture of semiconductors, photovoltaic cells, and flat panel displays. Using atmospheric observations from eight monitoring stations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and inverse modeling with a global 3-D atmospheric chemical transport model (GEOS-Chem), we quantify global and regional NF emission from 2015 to 2021. We find that global emissions have grown from 1.

Sustained growth of sulfur hexafluoride emissions in China inferred from atmospheric observations.

Sulfur hexafluoride (SF) is a potent greenhouse gas. Here we use long-term atmospheric observations to determine SF emissions from China between 2011 and 2021, which are used to evaluate the Chinese national SF emission inventory and to better understand the global SF budget. SF emissions in China substantially increased from 2.

Anthropogenic Chloroform Emissions from China Drive Changes in Global Emissions.

Emissions of chloroform (CHCl), a short-lived halogenated substance not currently controlled under the Montreal Protocol on Substances that Deplete the Ozone Layer, are offsetting some of the achievements of the Montreal Protocol. In this study, emissions of CHCl from China were derived by atmospheric measurement-based "top-down" inverse modeling and a sector-based "bottom-up" inventory method. Top-down CHCl emissions grew from 78 (72-83) Gg yr in 2011 to a maximum of 193 (178-204) Gg yr in 2017, followed by a decrease to 147 (138-154) Gg yr in 2018, after which emissions remained relatively constant through 2020.

Historical trend of ozone-depleting substances and hydrofluorocarbon concentrations during 2004-2020 derived from satellite observations and estimates for global emissions.

Global concentrations (or mole fractions) and emissions of ozone-depleting substances (ODSs) and their hydrofluorocarbon (HFCs) substitutes that are controlled by the Montreal Protocol and its Amendments and adjustments (MP) are of great interest to both the scientific community and public. Previous studies on global concentrations and emissions have mostly relied on ground-based observations. Here, we assess the global concentrations and emissions of eight MP controlled substances and methyl chloride from ACE-FTS (Atmospheric Chemistry Experiment high-resolution infrared Fourier transform spectrometer) satellite observations: CFC-11 (CFCl), CFC-12 (CFCl), CCl, HCFC-22 (CHClF), HCFC-141b (CHClF), HCFC-142b (CHClF), HFC-23 (CHF), HFC-134a (CHF), and CHCl.

A renewed rise in global HCFC-141b emissions between 2017-2021.

Global emissions of the ozone-depleting gas HCFC-141b (1,1-dichloro-1-fluoroethane, CHCClF) derived from measurements of atmospheric mole fractions increased between 2017 and 2021 despite a fall in reported production and consumption of HCFC-141b for dispersive uses. HCFC-141b is a controlled substance under the Montreal Protocol, and its phase-out is currently underway, after a peak in reported consumption and production in developing (Article 5) countries in 2013. If reported production and consumption are correct, our study suggests that the 2017-2021 rise is due to an increase in emissions from the bank when appliances containing HCFC-141b reach the end of their life, or from production of HCFC-141b not reported for dispersive uses.

Warming and redistribution of nitrogen inputs drive an increase in terrestrial nitrous oxide emission factor.

Anthropogenic nitrogen inputs cause major negative environmental impacts, including emissions of the important greenhouse gas NO. Despite their importance, shifts in terrestrial N loss pathways driven by global change are highly uncertain. Here we present a coupled soil-atmosphere isotope model (IsoTONE) to quantify terrestrial N losses and NO emission factors from 1850-2020.

Rapid increase in dichloromethane emissions from China inferred through atmospheric observations.

With the successful implementation of the Montreal Protocol on Substances that Deplete the Ozone Layer, the atmospheric abundance of ozone-depleting substances continues to decrease slowly and the Antarctic ozone hole is showing signs of recovery. However, growing emissions of unregulated short-lived anthropogenic chlorocarbons are offsetting some of these gains. Here, we report an increase in emissions from China of the industrially produced chlorocarbon, dichloromethane (CHCl).

Strong Southern Ocean carbon uptake evident in airborne observations.

The Southern Ocean plays an important role in determining atmospheric carbon dioxide (CO), yet estimates of air-sea CO flux for the region diverge widely. In this study, we constrained Southern Ocean air-sea CO exchange by relating fluxes to horizontal and vertical CO gradients in atmospheric transport models and applying atmospheric observations of these gradients to estimate fluxes. Aircraft-based measurements of the vertical atmospheric CO gradient provide robust flux constraints.

H in Antarctic firn air: Atmospheric reconstructions and implications for anthropogenic emissions.

The atmospheric history of molecular hydrogen (H) from 1852 to 2003 was reconstructed from measurements of firn air collected at Megadunes, Antarctica. The reconstruction shows that H levels in the southern hemisphere were roughly constant near 330 parts per billion (ppb; nmol H mol air) during the mid to late 1800s. Over the twentieth century, H levels rose by about 70% to 550 ppb.

Unexpected nascent atmospheric emissions of three ozone-depleting hydrochlorofluorocarbons.

Global and regional atmospheric measurements and modeling can play key roles in discovering and quantifying unexpected nascent emissions of environmentally important substances. We focus here on three hydrochlorofluorocarbons (HCFCs) that are restricted by the Montreal Protocol because of their roles in stratospheric ozone depletion. Based on measurements of archived air samples and on in situ measurements at stations of the Advanced Global Atmospheric Gases Experiment (AGAGE) network, we report global abundances, trends, and regional enhancements for HCFC-132b ([Formula: see text]), which is newly discovered in the atmosphere, and updated results for HCFC-133a ([Formula: see text]) and HCFC-31 ([Formula: see text]ClF).

A comprehensive quantification of global nitrous oxide sources and sinks.

Nitrous oxide (NO), like carbon dioxide, is a long-lived greenhouse gas that accumulates in the atmosphere. Over the past 150 years, increasing atmospheric NO concentrations have contributed to stratospheric ozone depletion and climate change, with the current rate of increase estimated at 2 per cent per decade. Existing national inventories do not provide a full picture of NO emissions, owing to their omission of natural sources and limitations in methodology for attributing anthropogenic sources.

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

Unregulated chlorocarbons, here defined as dichloromethane (CHCl), perchloroethene (CCl), chloroform (CHCl), and methyl chloride (CHCl), are gases not regulated by the Montreal Protocol. While CHCl 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.

Increase in global emissions of HFC-23 despite near-total expected reductions.

Under the Kigali Amendment to the Montreal Protocol, new controls are being implemented to reduce emissions of HFC-23 (CHF[Formula: see text]), a by-product during the manufacture of HCFC-22 (CHClF[Formula: see text]). Starting in 2015, China and India, who dominate global HCFC-22 production (75% in 2017), set out ambitious programs to reduce HFC-23 emissions. Here, we estimate that these measures should have seen global emissions drop by 87% between 2014 and 2017.

Recent Trends in Stratospheric Chlorine From Very Short-Lived Substances.

Very short-lived substances (VSLS), including dichloromethane (CHCl), chloroform (CHCl), perchloroethylene (CCl), and 1,2-dichloroethane (CHCl), are a stratospheric chlorine source and therefore contribute to ozone depletion. We quantify stratospheric chlorine trends from these VSLS (VSLCl) using a chemical transport model and atmospheric measurements, including novel high-altitude aircraft data from the NASA VIRGAS (2015) and POSIDON (2016) missions. We estimate VSLCl increased from 69 (±14) parts per trillion (ppt) Cl in 2000 to 111 (±22) ppt Cl in 2017, with >80% delivered to the stratosphere through source gas injection, and the remainder from product gases.

Continued Emissions of the Ozone-Depleting Substance Carbon Tetrachloride From Eastern Asia.

Carbon tetrachloride (CCl) is an ozone-depleting substance, accounting for about 10% of the chlorine in the troposphere. Under the terms of the Montreal Protocol, its production for dispersive uses was banned from 2010. In this work we show that, despite the controls on production being introduced, CCl emissions from the eastern part of China did not decline between 2009 and 2016.

Chemical evidence of inter-hemispheric air mass intrusion into the Northern Hemisphere mid-latitudes.

The East Asian Summer Monsoon driven by temperature and moisture gradients between the Asian continent and the Pacific Ocean, leads to approximately 50% of the annual rainfall in the region across 20-40°N. Due to its increasing scientific and social importance, there have been several previous studies on identification of moisture sources for summer monsoon rainfall over East Asia mainly using Lagrangian or Eulerian atmospheric water vapor models. The major source regions for EASM previously proposed include the North Indian Ocean, South China Sea and North western Pacific.

Deriving Global OH Abundance and Atmospheric Lifetimes for Long-Lived Gases: A Search for CHCCl Alternatives.

An accurate estimate of global hydroxyl radical (OH) abundance is important for projections of air quality, climate, and stratospheric ozone recovery. As the atmospheric mixing ratios of methyl chloroform (CHCCl) (MCF), the commonly used OH reference gas, approaches zero, it is important to find alternative approaches to infer atmospheric OH abundance and variability. The lack of global bottom-up emission inventories is the primary obstacle in choosing a MCF alternative.

Atmospheric observations show accurate reporting and little growth in India's methane emissions.

Changes in tropical wetland, ruminant or rice emissions are thought to have played a role in recent variations in atmospheric methane (CH) concentrations. India has the world's largest ruminant population and produces ~ 20% of the world's rice. Therefore, changes in these sources could have significant implications for global warming.

Role of atmospheric oxidation in recent methane growth.

The growth in global methane (CH) concentration, which had been ongoing since the industrial revolution, stalled around the year 2000 before resuming globally in 2007. We evaluate the role of the hydroxyl radical (OH), the major CH sink, in the recent CH growth. We also examine the influence of systematic uncertainties in OH concentrations on CH emissions inferred from atmospheric observations.

Growth in stratospheric chlorine from short-lived chemicals not controlled by the Montreal Protocol.

We have developed a chemical mechanism describing the tropospheric degradation of chlorine containing very short-lived substances (VSLS). The scheme was included in a global atmospheric model and used to quantify the stratospheric injection of chlorine from anthropogenic VSLS ( ClyVSLS) between 2005 and 2013. By constraining the model with surface measurements of chloroform (CHCl), dichloromethane (CHCl), tetrachloroethene (CCl), trichloroethene (CHCl), and 1,2-dichloroethane (CHClCHCl), we infer a 2013 ClyVSLS mixing ratio of 123 parts per trillion (ppt).

Reconciling reported and unreported HFC emissions with atmospheric observations.

We infer global and regional emissions of five of the most abundant hydrofluorocarbons (HFCs) using atmospheric measurements from the Advanced Global Atmospheric Gases Experiment and the National Institute for Environmental Studies, Japan, networks. We find that the total CO2-equivalent emissions of the five HFCs from countries that are required to provide detailed, annual reports to the United Nations Framework Convention on Climate Change (UNFCCC) increased from 198 (175-221) Tg-CO2-eq ⋅ y(-1) in 2007 to 275 (246-304) Tg-CO2-eq ⋅ y(-1) in 2012. These global warming potential-weighted aggregated emissions agree well with those reported to the UNFCCC throughout this period and indicate that the gap between reported emissions and global HFC emissions derived from atmospheric trends is almost entirely due to emissions from nonreporting countries.