Chloromethanes in the North American troposphere and lower stratosphere over the past two decades

Aircraft observations of the four chloromethanes: carbon tetrachloride (CCl4), methyl chloride (CH3Cl), dichloromethane (CH2Cl2), and chloroform (CHCl3), collected over North America between 2000 and 2022, were used to evaluate their vertical distributions and temporal trends in the atmosphere. We examine the vertical profiles, from the surface to the lower stratosphere (LS), of these increasingly important contributors to ozone-depleting chlorine in both altitude and potential temperature space. Airborne chloromethane trends were compared with those measured at long-term, ground-based monitoring stations. Below 20 km altitude, CCl4 trends were decreasing at all levels studied in the North American atmosphere (-1.1 ppt yr(-1)). CHCl3 and CH2Cl2 airborne observations were comparable to ground network measurements: CHCl3 increased between 2000 and 2018 and then decreased leading to a negligible trend over the 22 years studied and CH2Cl2 has been increasing at all levels in the troposphere (+2.41 ppt yr(-1), 2000-2022, <20 km).

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Author Smith, K.
Atlas, E.
Apel, Eric C.
Blake, D. R.
Dutton, G.
Hornbrook, Rebecca
Montzka, S.
Mühle, J.
Schauffler, Sue
Treadaway, V.
Publisher UCAR/NCAR - Library
Publication Date 2024-08-16T00:00:00
Digital Object Identifier (DOI) Not Assigned
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Topic Category geoscientificInformation
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Metadata Date 2025-07-10T19:59:26.997595
Metadata Record Identifier edu.ucar.opensky::articles:27419
Metadata Language eng; USA
Suggested Citation Smith, K., Atlas, E., Apel, Eric C., Blake, D. R., Dutton, G., Hornbrook, Rebecca, Montzka, S., Mühle, J., Schauffler, Sue, Treadaway, V.. (2024). Chloromethanes in the North American troposphere and lower stratosphere over the past two decades. UCAR/NCAR - Library. https://n2t.org/ark:/85065/d7th8rx0. Accessed 04 August 2025.

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