Project Summary/Abstract Benzene is a known carcinogen linked to leukemia with primary entry into the human body via the lungs, thus detecting, tracking and localizing emission sources in real-time are critical for preventing personal exposures. Premature death from air pollution (due to household air, ambient particulates and ozone) has increased drastically over the past two decades and was responsible for over 6.7 million deaths in 2019. The complexity and high operational cost of existing laborious measurement tools for benzene are responsible for infrequent air sampling activities. The lack of a real-time continuously monitoring benzene instrument for ambient air is making the impact of environmental exposures on the general population very difficult to assess. An easily-operating instrument capable of measuring benzene continuously in real-time with sensitivity of parts-per-billion by volume (ppbv) and adaptable to typical survey modalities (e.g. mobile, fixed, and walking) is the overall goal of this research and development program. The proposed project will improve both scientific knowledge on the impact of benzene on the health of the general population and technical capability in the measurement of benzene in real-time with high-sensitivity and fast time response. The Phase I Specific Aims are to engineer a laboratory prototype to detect benzene, establish the performance of the laboratory prototype, and demonstrate operations in outdoor urban environments. This proposed benzene detector will take advantage of key enabling technologies including recently available room-temperature quantum cascade lasers, custom compact system electronics designs, rugged multipass measurement cell designs, and data analytics for estimating emission rate and source. This real-time continuously monitoring benzene detector will enhance the understanding of its impact on human to reduce or eliminate cancers caused by exposure to benzene.