Atmospheric chemistry and the study of pollution are currently at a crossroads. Traditionally communities have investigated distinct issues; for example, regional air quality, intercontinental transport, micro-scale and molecular processes, global remote sensing, and gas-particle-climate connections. Within each area, knowledge has deepened through advances in basic science and technology. Modeling has evolved rapidly with the help of faster computers, improved parameterizations, and a better knowledge of many of the processes required for credible simulations. Experimentally, sensitive, accurate instrumentation has been developed to measure hundreds of trace species in gas and aerosol phases. Satellite remote sensing can be used to track the intercontinental transport of smoke, dust, haze, and ozone and several of its precursors, such as CO, NO2, and related gases. Researchers in remote field experiments can forecast pollution, view near-real-time satellite imagery, and predict the history of air parcels that may be sampled from aircraft or other platforms. A schematic is shown in Figure 1.