AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Air Quality Impacts of a Scheduled 36-hour Closure of a Major Highway
DAVID QUIROS, Qunfang Zhang, Suzanne Paulson, Rui Wang, Wonsik Choi, Arthur Winer, Yifang Zhu, University of California Los Angeles
Abstract Number: 18 Working Group: Urban Aerosols
Abstract On the July 16-17, 2011 weekend, a major Los Angeles highway, the I-405, was closed 36 hours for an overpass demolition. During this event we measured ultrafine particles (UFPs, < 0.1 micro-meters) and other air pollutants upwind, downwind, and at various distances of the I-405 pre-, during-, and post-closure using both fixed site and mobile platform monitors. We observed ~90% and ~40% traffic flow reductions on I-405 during closure on Saturday and Sunday, and ~20% reductions on the immediately adjacent Sepulveda Boulevard. During-closure downwind particle number concentration (PNC) decreased 73%, mass concentration (PM2.5) decreased 44%, and black carbon (BC) decreased 48%. We found traffic density (vehicles distance) correlated well with downwind BC (R-square=0.71). Daily average particle size distributions downwind were bimodal with pronounced nucleation and accumulation mode peaks during non-closure conditions and unimodal with an accumulation mode peak during closure conditions on Saturday July 16. We compared our current data to a similar dataset from 2001 and found that, over this 10-year period, the downwind-to-upwind PNC ratio decreased ~40%, but weekday traffic flow increased ~20%. This translates into an ~50% PNC reduction per-vehicle from the I-405 transit corridor. We speculate this decrease may have been from reduction of sulfur content in diesel fuels (from 500 to 15 ppm in 2006), the increased California Low-Emission Vehicle standards, and retirement of older vehicles.