Integrated monitoring of road traffic and airborne ultrafine particles at a camera-equipped urban intersection

Abstract

This study investigated ultrafine particle concentrations at a busy intersection in Braunschweig, Germany, highlighting the influence of traffic as the primary source of elevated ultra-fine particle (UFP) concentrations. A mobile lab, equipped with online instruments for combustion gases and aerosols (SMPS, EEPS) was operated near to the intersection. By coupling a high-resolution particle size spectrometer with a catalytic stripper, it effectively characterized short-lived traffic-related particle events, outperforming traditional methods in resolving high-emission events. While total concentrations of particles with diameters between 4 nm and 3 μm were in the range of 6,000 #/cm³ at low-traffic night hours, peak concentrations up to 3∗10⁶ #/cm³ (10–20 s duration) could be observed under heavy traffic conditions. During daytime traffic, approximately 10 %–30 % of particles could not be evaporated at 350 °C. Traffic analysis was performed on a four-lane intersection equipped with 14 vertical stereo-camera-systems that allows a precise characterization of the traffic situation. While combining high-resolution particle measurements with a camera system showed potential for classifying transport modes, challenges such as limited differentiation between emission sources and complex data interpretation reduced its overall effectiveness compared to conventional methods.