  The presence of chlorofluorocarbons (CFCs) in Earth's atmosphere is a direct
result of technology. Ozone-depleting CFCs have been banned by most countries,
but some CFCs have persistent in elevated concentrations due to their long
stratospheric lifetimes. CFCs are effective greenhouse gases and could serve as
a remotely detectable spectral signature of technology. Here we use a
three-dimensional climate model and a synthetic spectrum generator to assess
the detectability of CFC-11 and CFC-12 as a technosignature on exoplanets. We
consider the case of TRAPPIST-1e as well as a habitable Earth-like planet
around a 3300 K M-dwarf star, with CFC abundances ranging from one to five
times present-day levels. Assuming an optimistic James Webb Space Telescope
(JWST) Mid Infrared Instrument (MIRI) low resolution spectrometer (LRS) noise
floor level of 10 ppm to multiple co-added observations, we find that spectral
features potentially attributable to present or historic Earth-level CFC
features could be detected with a SNR $\ge 3-5$ on TRAPPIST-1e, if present, in
$\sim 100$ hours of in-transit time. However, applying a very conservative 50
ppm noise floor to co-added observations, even a 5x Earth-level CFC would not
be detectable no matter the observation time. Such observations could be
carried out simultaneously and at no additional cost with searches for
biosignature gases. Non-detection would place upper limits on the CFC
concentration. We find that with the launch of JWST, humanity may be
approaching the cusp of being able to detect passive atmospheric
technosignatures equal in strength to its own around the nearest stars.
