The major remaining uncertainty in climate projections stems from the aerosol-cloud-climate interactions in the atmosphere. Therefore, an accurate representation of aerosol particles and clouds is the foundation of any effort to forecast long-term climate change.

Aerosol particles in the urban atmosphere are especially important, in part because air pollution constitutes a public health crisis for over half of the world’s population, but also because the regional climate forcing associated with urban haze can be large. In this seminar, I will first show how aerosol particles are formed in cities, and how unregulated pollutants greatly increase their survival probability and contribution to urban clouds. Then, I will discuss my latest work on how anthropogenic pollution drives aerosol formation in the cold upper troposphere, which in turn may exert a broad climate impact across the Northern Hemisphere.