VPL Team members Ravi Kopparapu, Giada Arney, Jacob Haqq-Misra, and Jacob Lustig-Yaeger, recently submitted a new study for publication exploring the possibilities that pollutants such as Nitrogen Dioxide, could serve as a technosignature if observed in the atmosphere of a habitable exoplanet. Such observations, they say, could be done with a Earth-Sun like system at 10 pc away using proposed future space telescopes such as the LUVOIR or HabEx concepts.
You can find their paper, which has been summitted to ApJ, on arXiv here and read a NASA Press Release on their work here.