Evaluation of EDAR vehicle emissions remote sensing technology

Despite much work in recent years, vehicle emissions remain a significant contributor in many areas where air quality standards are under threat. Policy-makers are actively exploring options for next generation vehicle emission control and local fleet management policies, and new monitoring technologies to aid these activities. Therefore, we report here on findings from two separate but complementary blind evaluation studies of one new-to-market real-world monitoring option, HEAT LLC's Emission Detection And Reporting system or EDAR, an above-road open path instrument that uses Differential Absorption LIDAR to provide a highly sensitive and selective measure of passing vehicle emissions. The first study, by Colorado Department of Public Health and Environment and Eastern Research Group, was a simulated exhaust gas test exercise used to investigate the instrumental accuracy of the EDAR. Here, CO, NO, CH₄ and C₃H₈ measurements were found to exhibit high linearity, low bias, and low drift over a wide range of concentrations and vehicle speeds. Instrument accuracy was high (R² 0.996 for CO, 0.998 for NO; 0.983 for CH₄; and 0.976 for C₃H₈) and detection limits were 50 to 100ppm for CO, 10 to 30ppm for NO, 15 to 35ppmC for CH₄, and, depending on vehicle speed, 100 to 400ppmC₃ for C₃H₈. The second study, by the Universities of Birmingham and Leeds and King's College London, used the comparison of EDAR, on-board Portable Emissions Measurement System (PEMS) and car chaser (SNIFFER) system measurements collected under real-world conditions to investigate in situ EDAR performance. Given the analytical challenges associated with aligning these very different measurements, the observed agreements (e.g. EDAR versus PEMS R² 0.92 for CO/CO₂; 0.97 for NO/CO₂; ca. 0.82 for NO₂/CO₂; and, 0.94 for PM/CO₂) were all highly encouraging and indicate that EDAR also provides a representative measure of vehicle emissions under real-world conditions.