As our knowledge of the atmospheric chemistry of the SO2, NO, and NO2 continues to grow, it becomes increasingly clear that many different chemical reactions contribute to the oxidation of these oxides in the atmosphere. Solution phase and gas phase chemistry are both important to 'acid rain' development, and gas-solid, gas-liquid, liquid-solid as well as simple gaseous molecule interactions are seemingly important in some circumstances as well. The evaluation of the mechanism and rates of solution phase and heterogeneous pathways for SO2 and NOx oxidation within the troposphere, the significance of surface removal processes, and the transport and diffusion processes are much less amenable to simple laboratory studies and quantification. Although a significant wealth of important and necessary information related to SO2 and NOx chemistry has been defined in recent years and a reasonable depth of knowledge of the many fundamental gas phase processes exists today, many uncertainties still remain in this, the 'simplest' of the research areas related to 'acid rain' development.