Toward Portable and Affordable Air Quality Monitoring: A 3D-Printed Platform for Colorimetric NO ₂ Quantification from Vehicles’ Exhaust Emissions

Air pollution from vehicular exhaust emissions remains one of the main environmental and public health concerns in urban areas. Nitrogen dioxide (NO₂), a major component of combustion-related pollutants, is of particular concern due to its harmful effects and contribution to secondary atmospheric reactions. Its emissions from engines are continuously monitored to mitigate pollution and to support technological advances in vehicle energy sources. For this purpose, suitable sensor technologies must be developed to enable in situ analysis with ease of operation and compact design. This study presents the development and validation of a portable analytical platform designed for the quantification of gaseous NO₂ directly from vehicle exhaust emissions. The system was assembled using commercially available components and 3D-printed parts, employing a colorimetric detection method based on the Griess-Saltzman reaction combined with an ESP32-S3 microcontroller responsible for data acquisition and signal processing. Analytical parameters, such as sampling time and flow rate, were optimized to improve the efficiency of the NO₂ capture. The developed platform achieved a limit of detection of 0.6 ppbv and a limit of quantification of 2 ppbv for a sampling time of 20 min, ensuring high sensitivity for trace-level detection. Application of the device in real vehicle exhaust analysis revealed significant variations among fuel types, with diesel vehicles exhibiting NO₂ emissions substantially higher than those of gasoline-fueled ones. The results demonstrate the feasibility of using low-cost, portable systems for NO₂ monitoring, supporting their potential use in preliminary air quality assessments and urban pollution source identification.