This dissertation focuses on three subjects related to aerosol vertical profile, future climate change impacts on surface aerosol concentration and its effects on premature mortality and drought risk over California (CA). In Chapter 1, I investigate how convective mass flux and precipitation (wet removal) are associated with the aerosol vertical profile over the globe using Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observation (CALIPSO), Modern-Era Retrospective Analysis for Research and Applications (MERRA), European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim) and Global Precipitation Climatology Project (GPCP). The results indicate that convective mass flux is an important mechanism that influences global aerosol vertical distribution. In the tropics, more convective mass flux is associated with more aerosol above 500 hPa while less aerosol is related to less convective mass flux. More convective mass flux over the Northern Hemisphere mid-latitude emission sources is associated with more aerosol aloft (downwind). More (less) downward CMF is associated with more (less) aerosol in the lower troposphere and less (more) aerosol in the upper troposphere and vertical dispersivity over NH Pacific.

In Chapter 2, the response of surface fine particulate matter (PM2.5) concentration to greenhouse gas (GHG) induced warming at the end of century, and its effects on premature mortality related to respiratory diseases, is estimated. To conduct this work I use simulated PM2.5 from seven Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) models and five projected populations by Shared Socioeconomic Pathways (SSPs). Future climate change has a significant impact on surface PM2.5 concentration and the corresponding premature mortality. Both surface PM2.5 and premature mortality will likely increase at end of the 21st century under business-as-usual warming.

In Chapter 3, I investigate future drought risk over California using the Community Earth System Model Large Ensemble Community Project (CESM-LENS). This model is used because 1. it captures the observed teleconnection between El-Nino and California (CA) precipitation and 2. allows an assessment of the role of natural climate variability. The results suggest that under business-as-usual GHG emissions, drought risk during the 21st century does not significantly increase.

This thesis is composed of two parts. In the first part we investigate the impact of Saharan dust on North Atlantic marine stratocumulus clouds (MSc) using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), Clouds and the Earth's Radiant Energy System (CERES), and European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim). To calculate the aerosol- cloud radiative effect, we use two different methods These two methods yield similar results that Saharan dust modifies MSc in a way that acts to cool the planet. There is a strong seasonal variation, with the aerosol-cloud radiative effect switching from significantly negative during the boreal summer to weakly positive during boreal winter.

When most dust resides above the clouds during summer, aerosol-cloud microphysical effects that involve the co-location of aerosol and cloud, such as the second aerosol indirect effect, would likely be muted relative to the SDE. Moreover, the positive value of the aerosol-cloud radiative effect during winter, when most dust resides within MSc, indicates that the semi-direct effect is dominant$-$ that is the only mechanism by a negative aerosol-cloud radiative effect can be obtained.

We conclude that aerosol-cloud radiative effects associated with Saharan dust and North Atlantic MSc are dominated by the semi-direct effect.