Nitrogen dioxide (NO2) is a harmful air pollutant that poses significant risks to human health. Real-time monitoring of NO₂ concentrations in indoor environments with potential NO₂ sources is crucial for ensuring public health. This study presents an automated nitrogen dioxide monitoring method that integrates machine vision-based colorimetry with a low-flow solution delivery system utilizing a peristaltic pump. The system performs automatic control of both solution delivery and image acquisition for NO₂ detection. A calibration curve established between the G-value difference of the blank and sampled solutions and the NO₂ concentration yields an r-value of 0.993. The relative error of the automated device remains below 30% when NO2 concentrations in ambient air exceed 0.04 mg/m3.