Assessment of Near-Roadway NO2 Concentrations

This report contains an assessment by Sonoma Technology, Inc. of two near-road emission data studies conducted by others. In the first study, near-road Nitrogen dioxide (NO2) concentrations were measured in Las Vegas, NV, over one year between September 2007 and September 2008 at an elementary school located next to the US 95 freeway. The measurement site was 37 m from the edge of the road with a sound wall between the site and the road. The sample inlet was at the height of the top of the sound wall. US 95 is the road with a sound wall between the site and the road. The sample inlet was at the height of the top of the sound wall. Approximately 12% of the traffic on US 95 in 2007-2008 was heavy-duty diesel vehicles. In the second study, measurements next to interstate freeway I-710 near Los Angeles were made between February 2009 and March 2012, with winter and summer intensive measurement studies taking place in 2009. The majority of the analysis presented in this report focused on the intensive study periods. I-710 is a major trucking route to and from the Port of Long Beach, with annual average daily traffic ranging between 187,000 and 191,000 during 2009-2011 and with approximately 17-18% of the traffic comprising heavy-duty diesel vehicles. This study demonstrated that while both sites were below the 1-hr NO2 National Ambient Air Quality Standards (NAAQS), a reduction of the NAAQS to 80 ppb would likely cause the Los Angeles location to be above the standard. The data suggest that wind direction, wind speed, proximity of the monitor to the roadway, traffic patterns, total vehicle counts, fraction of heavy-duty diesel vehicles, urban background ozone concentrations, and urban background NO2 concentrations were the key factors influencing near-road NO2 concentrations.