Combustion sources, including anthropogenic (e.g. vehicles) and natural (e.g. wildland fires) sources are major emitters of carbonaceous aerosol (CA) into the atmosphere. CA, which includes organic aerosol (OA) and black carbon (BC), has a significant effect on the Earth’s radiative balance. BC is a strong absorber of solar radiation and exhibits a global warming effect. On the other hand, OA is mixture of organic components with variable optical properties. Some OA components only scatter solar radiation and have a strong cooling effect, while others (brown carbon, BrC) also absorb solar radiation and can have a net cooling or warming effect. This PhD dissertation focuses on improving the understanding of the climate and public health impacts of combustion CAs. The Weather Research and Forecasting model with chemistry (WRF-Chem) is used as a regional climate model. The month of August 2015 featured extensive wildfires in the Northwestern U.S., with the majority of CA, including BrC, over the U.S. dominated by emissions from these wildfires. We performed parallel simulations that (1) did not account for BrC absorption, (2) accounted for BrC absorption, and (3) accounted for BrC absorption as well as its decay due to photobleaching. A set of optical properties, namely the aerosol absorption optical depth (AAOD) and absorption Ångström exponent (AAE) is used to constrain the model output against observations. We found that accounting for BrC absorption and photobleaching resulted in the best agreement with observations. We also focused on CA emissions from gasoline vehicles. Gasoline direct injection (GDI) engines emit higher levels of BC compared to traditional port fuel injection (PFI) engines. Here, we performed simulations to estimate the aerosol-induced public health and direct radiative effects of shifting the U.S. fleet from PFI to GDI technology. The results show that the total annual deaths in the U.S. attributed to particulate gasoline-vehicle emissions would increase from 855 to 1599 due to shifting from PFI to GDI. Furthermore, the increase in BC associated with the shift would lead to an annual average positive radiative effect over the U.S. of +0.075 W/m2, with values as large as +0.45 W/m2 over urban regions.