In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 20, No. 16 ( 2020-08-20), p. 9771-9782
Abstract:
Abstract. We present new observations of trace gases in the stratosphere
based on a cost-effective sampling technique that can access much higher
altitudes than aircraft. The further development of this method now provides
detection of species with abundances in the parts per trillion (ppt) range
and below. We obtain mixing ratios for six gases (CFC-11, CFC-12, HCFC-22,
H-1211, H-1301, and SF6), all of which are important for understanding
stratospheric ozone depletion and circulation. After demonstrating the
quality of the data through comparisons with ground-based records and
aircraft-based observations, we combine them with the latter to demonstrate
its potential. We first compare the data with results from a global model driven
by three widely used meteorological reanalyses. Secondly, we focus on CFC-11
as recent evidence has indicated renewed atmospheric emissions of that
species relevant on a global scale. Because the stratosphere represents the
main sink region for CFC-11, potential changes in stratospheric circulation
and troposphere–stratosphere exchange fluxes have been identified as the
largest source of uncertainty for the accurate quantification of such
emissions. Our observations span over a decade (up until 2018) and therefore
cover the period of the slowdown of CFC-11 global mixing ratio decreases
measured at the Earth's surface. The spatial and temporal coverage of the
observations is insufficient for a global quantitative analysis, but we do
find some trends that are in contrast with expectations, indicating that the
stratosphere may have contributed to the slower concentration decline in
recent years. Further investigating the reanalysis-driven model data, we find
that the dynamical changes in the stratosphere required to explain the
apparent change in tropospheric CFC-11 emissions after 2013 are possible
but with a very high uncertainty range. This is partly caused by the high
variability of mass flux from the stratosphere to the troposphere,
especially at timescales of a few years, and partly by large differences
between runs driven by different reanalysis products, none of which agree
with our observations well enough for such a quantitative analysis.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-20-9771-2020
DOI:
10.5194/acp-20-9771-2020-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2020
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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