Abstract: Atmospheric hexavalent chromium (Cr-VI), which is highly toxic and carcinogenic, is emitted from both anthropogenic and natural sources. Chromium is among the top five most abundant metals in diesel particles, and thus, the Meadowlands district, which is located close to the NJ Turnpike (NJTPK) with high truck traffic volume, may have an elevated Cr-VI concentration. Also, the Meadowlands district is located ~5 miles from Kearny and ~10 miles from Jersey City, areas with more than 200 historic chromium waste sites. The Cr-VI contaminated fine particles may be transported to the Meadowlands area and contribute to Cr-VI pollution. However, Cr-VI was not measured in air quality monitoring programs. Also, the detailed particle size distribution of Cr-VI in ambient air was not characterized. This pilot study measured the Cr-VI concentration in PM2.5 for 2 weeks simultaneously at two sites, the MRRI site and the Williams site, during one winter and summer season. Cr-VI was detected in all of the field samples, with a mean±SD (median) of 0.52±0.32 (0.47) ng/m3 at the MRRI site and 0.40±0.20 (0.35) ng/m3 at the Williams site. The Cr-VI distribution as a function of particle size at the Williams site was also determined by using a MOUDI sampler with 8 particle sizes. It was found that the Cr-VI was concentrated in the particles with a diameter less than 2.5 μm. The impact of truck traffic on the NJTPK as well as temperature and humidity on the Cr-VI levels was examined and the results and implication will be discussed.