Particle Concentrations (PM10, PM2.5) in Subways, Light Rail Trains and Platforms in the Los Angeles Metro System

KALAM CHEUNG (1), Winnie Kam (1), Nancy Daher (1), Constantinos Sioutas (1)

(1) University of Southern California, Los Angeles

     Abstract Number: 397
     Last modified: May 11, 2010

Abstract
Recent studies in urban megacities suggest that particulate matter (PM) in public mass transit systems is different from urban ambient PM concentrations. PM mass concentrations in urban subway systems have been reported to be higher than the above-ground companion sites. In particular, potentially toxic transition metals and elements can be present in concentrations up to 100 times greater than those typically observed in urban air dominated by traffic emissions. The primary objective of this study is to conduct PM measurements in the Los Angeles Metro system to quantify the mass concentrations, chemical and toxicological characteristics of respirable PM concentrations in its subway and light rail lines.

Over the course of the sampling campaign (May-July 2010), size-resolved (coarse and fine) PM is collected using the Personal Cascade Impactor System (PCIS) in both the metro system and a fixed site (USC) in downtown Los Angeles. In addition, real-time particle mass concentrations (PM 10 and PM 2.5) are measured in the subway and light rail lines by TSI DustTraks. Preliminary analysis of the continuous data shows that PM 2.5 concentrations at the stations are always higher (1.2 - 4.7 times and 1.3 - 5.8 times in the subway and light rail lines, respectively) than the in-train levels, indicating that a substantial portion of the PM exposure might occur while waiting in stations, despite the relatively shorter time spent in these platforms compared with in-train commute. The PM 2.5 mass concentrations calculated from gravimetric measurements are on average 33, 16 and 23 µg/m3 for the subway, light rail and the USC fixed site, respectively. The subway line has also the highest average coarse PM mass concentration of 14 µg/m3, contributing to 29% of the overall PM 10 mass. The collected PM will be used to assess the chemical composition and toxicological potential, and the results will comprise the first comprehensive dataset in subway and light rail lines of the Los Angeles Metro system.