Concentration of Ultrafine Particles near Roadways in An Urban Area in Chicago, Illinois

Monitoring ambient concentrations of ultrafine particles (UFPs) is important due to their negative impact on human health. This paper provides measurements of UFP concentrations near roadways because emissions from light duty vehicles (LDVs) and heavy duty vehicles (HDVs) have been shown to be a major source of UFPs. The concentration of UFPs was measured near two different roadways in Chicago IL for 2 to 4 hours on 52 days between 2014 and 2016. One of the sites was restricted to LDVs (Lake Shore Drive, LSD) and had a near roadway concentration from vehicles (background subtracted) that averaged nearly 8,000 particles cm–3. The other site had a mix of LDVs and HDVs (Dan Ryan Expressway, DRE) and the near roadway concentration from the vehicle fleet (background subtracted) averaged nearly 11,000 particles cm–3. The contribution of UFPs from HDVs was almost 80% of the total emissions on the DRE demonstrating that HDVs emit many more UFPs than LDVs. Background concentrations of UFP were measured upwind of the near roadway sampling sites and were subtracted from the near roadway measurements in order to determine the vehicle contribution to the total UFP concentration. The background concentrations varied with wind direction and therefore were divided into ambient background categories based on wind direction. The four different background categories are defined as remote, lake, industrial and urban. Each category has a distinct different average ambient background concentration (particles cm–3) as follows: remote, 2,700; lake, 6,000; industrial 12,000 and urban 11,000. The large background concentrations in urban areas indicate that total near roadway measurements are generally near 20,000 particles cm–3 with 50 to 60% from vehicles and reach to 60,000 particles cm–3 depending on the background and traffic emission. The results indicate high UFP readings near roadway and one possible solution is mitigation of traffic congestion.