Unexplained high and persistent methyl bromide emissions in China.

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Ozone Layer Research

Background:

• Methyl bromide (CH3Br) is a significant ozone-depleting substance regulated globally.
• Accurate quantification of CH3Br emissions is crucial for monitoring Montreal Protocol compliance and ozone layer recovery.
• The spatial and temporal distribution of CH3Br emissions in China has not been clearly understood.

Purpose of the Study:

• To estimate national CH3Br emissions in China from 2011 to 2020 using atmospheric observations.
• To compare top-down emission estimates with bottom-up inventory data.
• To identify the contribution of underestimated or unidentified sources to CH3Br emissions.

Main Methods:

• Utilized atmospheric observations from 10 monitoring sites across China.
• Employed an atmospheric inversion technique for top-down emission estimation.
• Compared results with an updated bottom-up inventory of identified emission sources.

Main Results:

• Observed significantly enhanced CH3Br mole fractions, particularly in eastern China.
• Top-down emission estimates were 5.5 ± 1.4 gigagrams per year higher than bottom-up estimates.
• Approximately 60% of observed CH3Br emissions originated from underestimated or unidentified sources.

Conclusions:

• Significant unaccounted CH3Br emissions exist in China, impacting stratospheric ozone depletion.
• Findings have critical implications for assessing compliance with the Montreal Protocol.
• Further research is needed to identify and quantify previously unknown CH3Br emission sources.