The broader impact/commercial potential of this project lies in the widespread nature of the problem of airborne Black (BC) and Brown (BrC) carbon particulates. These are formed from combustion processes such as motor vehicles and ships, forest fires and biomass burning, as well as indoor cooking in developing countries. BC and BrC are important components of atmospheric aerosols (small airborne solid and liquid particles) that affect air quality, visibility and climate. The World Health Organization estimates that nearly 7 million premature deaths globally in 2012 were linked to air pollution, and black carbon-containing aerosols are often singled out as a major contributor due to their strong linkages to adverse health effects. Accurate and robust monitoring of BC (and BrC) at a lower cost is necessary in urban and industrial areas throughout the United States and abroad to provide adequate temporal and spatial measurements that can be used to assess regional air quality models and estimate community exposure risks. This information will then make it possible for local and regional government agencies to develop mitigation strategies that protect the health of their communities. This Small Business Innovation Research (SBIR) Phase I project addresses the problem of accurate and inexpensive Black Carbon (BC) measurements by developing a long-path photometer to quantify airborne BC and BrC particulates. The most common commercially-available technique for BC and BrC requires collection of particulates on a filter. This filter introduces numerous artefacts requiring complicated corrections. Other existing techniques are quite expensive and require significant expertise to operate. The Black Carbon Photometer (BCP) to be developed here will not require pre-concentration on a filter, thus providing a direct, correction-free measurement. It will be operationally simple and require little maintenance, similar to photometers routinely used in monitoring networks for gas phase species such as ozone. The initial BCP will be low power, portable and is projected to cost less than currently available BC analyzers. Thus, it should provide researchers in air quality and public health, as well as those in monitoring agencies, a practical and economical alternative to existing technologies.