Aerosol particles, solid or liquid particles suspended in the air, can affect Earth’s climate by scattering and absorbing sunlight. PM2.5, particles less than 2.5 micrometers in diameter, are largely responsible for degraded visibility and easily traverse respiratory system pathways causing adverse health effects in humans. Often, a majority of PM2.5 is composed of organic matter formed through photo-chemical reactions of hundreds of volatile organic compounds (VOC). This process depends on nitrogen oxide radical (NOX = NO + NO2) concentrations in the atmosphere, now predominantly contributed by anthropogenic emissions. NOX and VOC react to produce organic nitrates, thought to be significant contributors to PM2.5, but for which measurements are generally lacking. My project involves developing a concrete assessment of the role of organic nitrates as contributors to PM2.5. I am developing an analytical method to thermally desorb organic nitrates from atmospheric particles collected on filters and promptly decompose them into nitrogen dioxide (NO2). The resulting NO2 is measured with a Cavity Attenuated Phase Shift (CAPS) spectroscopy instrument. I am establishing whether there is a direct correlation between the concentration of organic nitrates in PM2.5 and desorbed NO2. The goal is to quantify organic nitrates without individually measuring each of the likely hundreds present in the ambient atmosphere. Moreover, the thermal desorption process provides information on the physical properties of organic nitrates, such as effective saturation vapor pressure, needed for air quality computer models to accurately simulate their contribution to PM2.5. As a result, I will help develop a better understanding of how natural and anthropogenic emissions affect the composition of the atmosphere by allowing assessments of how PM2.5 levels have changed in response to NOX emission reductions by the Clean Air Act.