التفاصيل البيبلوغرافية
| العنوان: |
Chloromethanes in the North American Troposphere and Lower Stratosphere Over the Past Two Decades. |
| المؤلفون: |
Smith, Kate1,2 (AUTHOR) katie.smith@noaa.gov, Atlas, Elliot1 (AUTHOR), Apel, Eric C.3 (AUTHOR), Blake, Donald R.4 (AUTHOR), Dutton, Geoff5 (AUTHOR), Hornbrook, Rebecca S.3 (AUTHOR), Montzka, Steve5 (AUTHOR), Mühle, Jens6 (AUTHOR), Schauffler, Sue3 (AUTHOR), Treadaway, Victoria1 (AUTHOR) |
| المصدر: |
Geophysical Research Letters. 8/16/2024, Vol. 51 Issue 15, p1-9. 9p. |
| مصطلحات موضوعية: |
*METHYL chloride, *CARBON tetrachloride, *OZONE layer depletion, *STRATOSPHERE, *TROPOSPHERIC aerosols, VIENNA Convention for the Protection of the Ozone Layer (1985). Protocols, etc., 1987 Sept. 15 |
| مستخلص: |
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). Plain Language Summary: Atmospheric processes can transport surface emissions of organic chlorine (Cl) compounds to higher altitudes, including the lower stratosphere (LS). At these high altitudes, organic Cl compounds will react, releasing the Cl radical. Subsequent Cl‐radical reactions can lead to the depletion of ozone. The ozone layer surrounds the globe at these high altitudes and is responsible for protecting life on the surface from harmful UV radiation. Therefore, it is important to have data on species containing organic Cl, especially those that are of increasing concern because their sources and sinks are not fully understood. We collect information about four different Cl‐containing species, three of which are not currently regulated by the Montreal Protocol and calculate how their abundances at different altitudes in the atmosphere have changed over 22 years. We use data collected from aircraft flights over North America and ground‐based monitoring sites within America to determine the mixing ratios of these species. Key Points: Evaluated chloromethane abundances over North American troposphere and lower stratosphereCollated 22 years of chloromethane measurements collected from airborne platformsCalculated trends from annual means at different atmospheric levels and were comparable to long‐term surface site measurements [ABSTRACT FROM AUTHOR] |
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