Absorption by atmospheric aerosols is the wild card for global climate change. Issues regarding atmospheric gases and aerosols have been at the forefront and the work presented within is directed at those issues. Specifically, work has been performed in order to help understand the issue of absorption in the atmosphere and whether this contributes towards positive forcing or warming of the atmosphere. In the process of conducting this research a custom, first-principles photoacoustic spectrometer was improved, calibrated and used extensively in order to obtain knowledge of the interaction of light with atmospherically relevant gases and make the first measurements of absorbing aerosols. The absorption cross-section of uncoated and coated soot was measured and quantified and found to be consistent with other work where amplifications on the order of nearly 100% were observed with uncertainty levels much lower than previously reported. Soot was also found to be optically thin where the total mass of the soot contributes to the absorption. Consequential to the soot work, the photoacoustic spectrometer developed to measure the absorption was utilized as a high precision greenhouse gas sensor. The photoacoustic spectrometer was found to produce results on the absorption of CO2 to within 3% of the theoretically predicted line profile Moreover, the photoacoustic spectrometer was used to determine measurable coating thicknesses of less than 10 nanometers on 100 nm soot particles.