Near‐Global CFC‐11 Trends as Observed by Atmospheric Infrared Sounder From 2003 to 2018

Abstract

Recent studies have indicated a slowdown of the decline of CFC-11 concentration since 2012. Ground-based observations used in such studies have their limitations in terms of global coverage. Here we show that the CFC-11 time-varying behaviors can be seen by double differencing nadir-view, clear-sky brightness temperatures of four AIRS (Atmospheric Infrared Sounder) channels in an infrared CFC-11 absorption band. Assuming that CFC-11 is vertically well mixed through the troposphere, we retrieve CFC-11 surface concentration and its secular trend using such AIRS observations over the near globe (55°S to 55°N) from January 2003 to December 2018. The retrieved trends of CFC-11 at the 11 ground sites agree well with the trends derived from in situ measurements at those sites. Our results show that, from 55°S to 55°N, the CFC-11 trends from January 2003 to December 2012 are all negative, ranging from −2.5 to −1 ppt/year. The trends from January 2003 to December 2018 are less negative by as much as 0.5-1 ppt/year over the Shandong peninsula, the Arabian Peninsula, and north India and Nepal area, and such differences in the trends are statistically significant. Factors other than the CFC-11 that can affect the retrievals and trends are also discussed. These findings can help us depict the near-global spatial distribution of the CFC-11 trends from 2003 to 2018. The analysis described here has the potential to be used with current and future hyperspectral sounders to help monitor the CFC-11 from space.

Identification of Short and Long‐Lived Atmospheric Trace Gases From IASI Space Observations

“…The absorption bands of the two CFCs, located around 849 cm −1 for CFC‐11 and at ∼923 and ∼1,161 cm −1 for CFC‐12 (here and also later, the wavenumbers refer to the position of strong Q‐branches), have whitened signals of 0.3, 0.7, and 0.9, respectively. Those positive values indicate that their atmospheric abundance was smaller in 2017 than in 2008, which is consistent with independent satellite measurements (Chen et al., 2020), independent in‐situ measurements (Prinn et al., 2018) and a direct consequence of the 1987 Montreal Protocol to limit the use and production of CFCs (World Meteorological Organization, 2018). The ν 3 band of CCl 4 shows up at ∼796 cm −1 with a whitened value of 0.2.…”

A New Halocarbon Absorption Model Based on HITRAN Cross‐Section Data and New Estimates of Halocarbon Instantaneous Clear‐Sky Radiative Forcing

“…This emphasizes the critical importance of monitoring the decline of these substances in response to the Montreal Protocol. For CFC11, in particular, the decline slowed after 2013 (see Chen et al., 2020, and references therein). Fortunately, newer studies indicate an again faster decline from 2019 on (Montzka et al., 2021; Park et al., 2021).…”

The Atmospheric Infrared Sounder

“…A wide variety of other algorithms are also in use within the research community for retrievals of geophysical quantities from the AIRS radiances [11,[16][17][18][19].…”

“…This has significant implications for air quality and human health, since NH 3 is a precursor for particulate matter (aerosol). AIRS radiances have also been used to examine spatial patterns in trends of CFC-11 (an important contributor to stratospheric ozone depletion) on a global scale [19]. While ground-based networks provide long-term measurements, they are too sparse to show the kind of spatial patterns visible from the satellite view.…”