This month's guest, Justin Stewart (@thecrobe), studies air quality and atmospheric microbial communities in Philadelphia, Pennsylvania. He tells us about how he got interested in microbes and about some of the challenges of studying these organisms in the air. He explains how several components of air quality (including ozone, PM2.5, and microbes) vary across the city, how they can affect human health and ecosystem function, and how those air quality might change in the face of extreme weather events and climate change. We discuss what the city has done to combat poor air quality (spoiler: not much) and whether microbes could actually play a role in helping to make the air safer for everyone to breathe. If you have questions, comments, or suggestions for future episodes, e-mail us at [email protected] or find us on Twitter @FutureCitiesPod. Learn more about the Urban Resilience to Extremes Sustainability Research Network (UREx SRN) at www.sustainability.asu.edu/urbanresilience. Listen on iTunes, Stitcher or Buzzsprout.