Overview: The atmosphere is composed of gases such as oxygen, nitrogen and carbon dioxide. Other gases are present at much lower concentrations and include ozone, nitrogen dioxide, sulfur dioxide and formaldehyde just to name a few. nitrogen oxides, sulfur oxides and formaldehyde just to name a few. Besides these gases, there is something else in the air we breathe, tiny microscopic particles called aerosols. Not just the aerosol that comes from spray cans that you are all probably familiar with but this talk will focus on any liquid or solid particles that is suspended in the air, which is the definition of an aerosol. These tiny particles come from many sources and can impact the Earth’s climate and human health in ways we are just starting to understand. In this talk I want to discuss the air we breathe in both indoor and outdoor environments, focusing on some of the newest research findings that have been recently published. Guest Speaker: Vicki H. Grassian, Ph.D., Executive Associate Dean, Division of Physical Sciences, UC San Diego. Vicki H. Grassian is currently a Distinguished Professor at the University of California San Diego with appointments in the Departments of Chemistry & Biochemistry, Nanoengineering and Scripps Institution of Oceanography and she holds the Distinguished Chair of Physical Chemistry within the Department of Chemistry and Biochemistry. She is also the co-Director of the Center for Aerosol Impacts on Climate and the Environment a multi-institutional NSF-Chemical Center of Innovation and the Executive Associate Dean for the Division of Physical Sciences. Prior to her appointments at the University of California San Diego she was a professor at the University of Iowa for 25 years. Professor Grassian has mentored hundreds of students in her laboratory including nearly thirty students who have received their PhDs under her guidance.