A long term portable gas detecting and monitoring apparatus includes a case having a continuous sidewall including a first end closed by a first end cap, and a second end closed by a second end cap connected sealably and removably to the continuous sidewall. The continuous sidewall is triangular between the closed end and the open having three sides and three corners, two of the three sides being straight and equal in length, one of the three sides being rounded, and each of the three corners being rounded. A long term gas detection and monitoring unit mounted in the case includes gas, and temperature and humidity sensors in communication with an ambient atmosphere outside the case, a data processor operatively connected to the sensors, data storage, an information display viewable through the case, and a calibration unit for calibrating the gas sensor to a predetermined gas concentration measured by the gas sensors.