Long Term Study of Urban Ultrafine Particles in Rochester, NY

Yungang Wang (1), Philip K. Hopke (1), David C. Chalupa (2), Mark J. Utell (2)

(1) Center for Air Resource Engineering and Science, Clarkson University (2) University of Rochester Medical Center

     Abstract Number: 65
     Last modified: October 10, 2009

Abstract
Particle number size distributions in the size range of 0.011 – 0.470 micro-meter have been continuously measured since late November 2001 at New York State Department of Environmental Conservation (NYS DEC) sites in Rochester, NY. From 2001 to March 2004, a downtown site (latitude 43°09'40" N, longitude 77°36'12" W) surrounded by an inner loop road within 0.5 miles was employed. In May 2004, a new site was established in eastern Rochester (latitude 43°08'46" N, longitude 77°32'53" W) adjacent to Interstate Highways I-490 and I-590. These are major traffic routes into downtown Rochester. The particle size distributions were measured using a scanning mobility particle sizer (SMPS). Hourly PM$_2.5 mass, SO$_2, CO, O$_3 concentrations, and meteorological parameters (wind speed, wind direction, ambient temperature and relative humidity) were also measured at the NYS DEC site throughout the study period. Ambient particle size distributions were also measured using a Wide-Range Particle Spectrometer (WPS, model M-1000XP, MSP Inc) since May 2004 at the Cardiac Rehabilitation Center (CRC) site located on the south side of Rochester.

The sites are approximately 5 miles apart. Correlation coefficients were calculated between the hourly particle number and ambient pollutant concentrations as well as the meteorological parameters measured at the DEC site. The correlations between particle number concentrations from both sites were also examined.

The average particle number concentration in the size range of 0.011 – 0.470 micro-meter in Rochester decreased by 36% from 2005 to 2008. The greatest reduction, 41%, was in the range of 0.011 – 0.050 micro-meter. Average PM$_2.5 mass concentration, SO$_2 concentration and CO concentration also decreased by 29%, 34%, and 20%, respectively. The monthly average particle number concentrations (Dp = 0.011 – 0.470 micro-meter) were higher in winter and early spring than the averages in summer months except for 2006 (no data in summer). However, the highest hourly average concentrations were generally observed in summer or early fall probably in the plume nucleation events (Dp = 0.011 – 0.100 micro-meter) in the presence of strong photochemical activity in summer months. There was a decrease in the afternoon concentrations of the 0.011 - 0.050 mirco-meter range that is likely related to the closure of Rochester Gas & Electric (RG&E) coal-fired power plant between February and April 2008.

Morning nucleation and growth events were more common in winter and spring than summer and fall. Similar meteorological conditions and relatively steady traffic volumes on both I-490 and I-590 were observed from year to year. A large decrease in 0.011 – 0.050 micro-meter particles during morning rush hour was observed. It can be hypothesized that this reduction is largely due to the transition to ultra-low sulfur (< 15 ppm sulfur) diesel fuel in the U.S. as of October 1, 2006. The weaker correlation of 0.011 – 0.050 micro-meter particle number concentrations (r = 0.44) than 0.050 – 0.100 micro-meter (r = 0.61) and 0.100 – 0.470 micro-meter particles (r = 0.74) between the DEC site and the CRC site shows that there may be some potential local UFP sources near the one or both sites.