Mapping the Spatial Distribution of 2.5 to 10 nm and Total Particle Concentrations on Highways, Secondary, and Tertiary Roads

JONAH HAZELWOOD, Lintong Cai, Stephanie Bachman, Nicholas Meskhidze, Markus Petters, North Carolina State University

     Abstract Number: 166
     Working Group: Urban Aerosols

Abstract
Ultrafine particles (UFPs), defined as particles with a diameter < 10 nm, are an area of growing interest due to their implications for air quality and human health. Previous studies suggested that vehicular emissions (particularly from diesel-fueled vehicles) are responsible for most emissions in urban environments. Exposure to UFPs is known to cause a variety of cardiovascular, respiratory, and neurological disorders. The airborne UFP dynamics involves particle emissions, dispersions, chemical and physical transformations in the atmosphere, and variabilities in local meteorological parameters. Here we show measurements from a mobile platform designed to map the spatial distribution of particles between 2.5 and 10 nm in diameter. The system deployed in Raleigh, NC consisted of 3 condensation particle counters (CPCs), a nano SMPS, a high-resolution GPS, a sonic anemometer, and a mobile power station. Traffic was observed using a dashboard camera. A composite map detailing gridded, averaged data from all sampling days was produced alongside a traffic volume map, illustrating a correlation between 2.5 to 10 nm particle concentrations and traffic flow in the city. It was found that tertiary roads (low-traffic residential areas) were relatively clean, with particle concentration < 2000 cm-3. Particle concentrations exceeding 700,000 cm-3 were observed intermittently on secondary roads and highways and attributed to a few super-emitter vehicles. Super-emitters (such as diesel trucks and scooters/motorcycles) were identified by geolocating the aerosol concentration data with traffic images. We found a high spatiotemporal variability of UFPs. Both 2.5 to 10 nm and total particle concentration varied by more than an order of magnitude within several seconds. Concentration dropped to background levels on roads 120 m from the highway. This talk will highlight the usefulness and limitations of mobile aerosol measurements for determining the emission of ultrafine particles from non-stationary sources.