Performance assessment and recommendations for motor vehicle emission remote sensing equipment in megacity conditions: Insights from Beijing

Remote sensing equipment (RSE) plays an essential role in monitoring vehicle emissions but requires comprehensive evaluation to verify reliability. In this study, the performance of seven different RSE models in Beijing was assessed by comparing their measurements with those of portable emission measurement systems (PEMS) and steady-state condition testing (SCT). Large variations were observed among the RSE models for CO (16 %-363 %), NO (2 %-354 %), and HC (10 %-725 %) emissions. Comparisons between RSE and PEMS revealed even more significant discrepancies for CO (20 %-6773 %), NO (15 %-2818 %), and HC (13 %-5477 %), with maximum deviations occurring at vehicle speeds between 20 and 60 km/h, reflecting the impacts of vehicle operation on emission measurements. The correlation between RSE and SCT was satisfactory for CO and NO (R² values of 0.64-0.76) but poor for HC (R2 = 0.16-0.22), primarily due to differences in measurement principles. Strengthening management, enhancing certification and accreditation, and regular consistency checks of RSE with SCT and PEMS are recommended for improved reliability in law enforcement applications.