We present here the development of a triethanolamine (TEA) nanocomposite-based chemiresistive gas sensor for detecting NO2 in the ambient environment. The detection mechanism is based on measuring resistivity changes that occur in a nanocomposite due to the absorption and continuous reaction of NO2 gas molecules with TEA. By incorporating carbon nanoparticles into the nanocomposite, NO2-induced resistance changes are amplified by the nanocomposite and measured. Based on calibration, the sensor has a calculated sensitivity of w50 parts per billion (ppbv) (limit of detection) to NO2 with a response time of 2 min. Sensor did not react with exposure to NO, O3, CO, CO2, and SO2. Sensor prototype is compact, cost effective, and has the capability of being modularized for field deployments, which are the key requirements for developing portable sensor technology for air quality monitoring.