Sullivan is a Professor in Chemistry and Mechanical Engineering at Carnegie Mellon University, with a courtesy appointment in Civil and Environmental Engineering. He is a member of the Center for Atmospheric Particle Studies. His research involves atmospheric chemistry, aerosol analysis, instrument development, and cloud nucleation studies. He uses optical tweezers and mass spectrometry to investigate particle properties and climate impacts. He has developed aircraft-deployable tools for real-time atmospheric monitoring. He holds a Ph.D. from UC San Diego and has 17 years of university teaching experience.