An autonomous, ground-based, integrated path, differential absorption light detection (IPDA) system is presented, capable of measuring multiple gases concentration in the atmosphere. The device was developed to monitor small scale locations with high greenhouse gases emissions and is equipped with three low optical power CW DFB diode lasers for the atmospheric detection of CO2, CH4, H2O. The system is capable to detect additional gases in the atmosphere by installing proper diode lasers in the near-infrared spectral range. A novel method calculating the concentration of gases is proposed based on the intensity of the H2O absorption line. The values calculated by this method were compared with those from DIAL equation are found to be in agreement. The device was tested on measuring background concentrations of the gases in the atmosphere.