Long-term study of urban ultrafine particles and other pollutants Yungang Wang a , Philip K. Hopke a, * , David C. Chalupa b , Mark J. Utell b a Center for Air Resource Engineering and Science, Clarkson University, Potsdam, NY 13699-5708, USA b Department of Environmental Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA article info Article history: Received 27 May 2010 Received in revised form 17 July 2010 Accepted 11 August 2010 Keywords: Ultrafine particles Urban Coal-fired power plant Diesel Highways Sulfur abstract Continuous measurements of number size distributions of ultrafine particles (UFPs) and other pollut- ants (PM 2.5 , SO 2 , CO and O 3 ) have been performed in Rochester, New York since late November 2001. The 2002e2009 average number concentrations of particles in three size ranges (10e50 nm, 50e100 nm and 100e500 nm) were 4730 cm 3 , 1838 cm 3 , and 1073 cm 3 , respectively. The lowest annual average number concentrations of particles in 10e50 nm and 50e100 nm were observed during 2008e2009. The lowest monthly average number concentration of 10e50 nm particles was observed in July and the highest in February. The daily patterns of 10e50 nm particles had two peaks at early morning (7e8 AM) and early afternoon (2 PM). There was a distinct declining trend in the peak number concentrations from 2002e2005 to 2008e2009. Large reductions in SO 2 concentrations associated with northerly winds between 2007 and 2009 were observed. The most significant annual decrease in the frequency of morning particle nucleation was observed from 2005 to 2007. The monthly variation in the morning nucleation events showed a close correlation with number concentrations of 10e50 nm particles (r ¼ 0.89). The frequency of the local SO 2 -related nucleation events was much higher before 2006. All of these results suggest significant impacts of highway traffic and industrial sources. The decrease in particle number concentrations and particle nucleation events likely resulted from a combination of the U.S. EPA 2007 Heavy-Duty Highway Rule implemented on October 1, 2006, the closure of a large coal- fired power plant in May 2008, and the reduction of Eastman Kodak emissions. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Ultrafine particles (UFPs, D p < 100 nm, Hinds, 1999) in the ambient atmosphere are of great concern because of their potential adverse health effects. UFPs have high particle number concen- tration and large surface area, and the potential for adsorbed or condensed toxic air pollutants when compared with larger parti- cles (Sioutas et al., 2005). Dosimetry studies have shown high deposition efficiencies for inhaled UFPs in human respiratory tract, translocation of UFPs to extrapulmonary organs, cardiovascular effects and pulmonary inflammation in humans and animals following UFP exposures (e.g. Oberdörster and Utell, 2002). Sources of UFPs in the urban ambient atmosphere include primary emis- sions of motor vehicles and coal-fired power plants (Morawska et al., 2008; Wehner et al., 1999; Zhu et al., 2002) and secondary particle nucleation (Brock et al., 2002; Holmes, 2007; Kulmala and Kerminen, 2008). Ogulei et al. (2007) and Kasumba et al. (2009) found that traffic, industrial emission and nucleation are the most important sources of UFPs in Rochester, New York. Urban UFP number concentrations obtained at different loca- tions worldwide are summarized in Table 1 . It is important to emphasize the lower particle size limits in each study because the number of particles is normally higher at the lower end of the particle size range. In the urban atmosphere, the number concen- trations of particles with diameters from 3 to 10,000 nm generally ranged from 6  10 3 cm 3 to 600  10 3 cm 3 . These values were generally larger than those measured at rural and clean background (e.g. Stanier et al., 2004a; Weijers et al., 2004). Particles in the size range of 10e30 nm (nuclei mode) are emitted in large numbers by diesel engines (Kittelson, 1998). A strong correlation between the number concentrations of UFPs and diesel traffic volume at a busy urban intersection has been reported (Wang et al., 2008). Wählin (2009) compared curbside UFP number size distributions in Copenhagen between 2002e2004 and 2005e2007. A decrease of 27% in UFP number concentration (especially in the size range <30 nm) was due to transition to sulfur-free (<10 ppm) diesel fuel and gasoline in Denmark on New Year’s Day 2005. In addition, particle nucleation events have been widely and frequently observed at urban sites (Jeong et al., 2004; * Corresponding author. Tel.: þ1 315 268 3861; fax: þ1 315 268 4410. E-mail address: hopkepk@clarkson.edu (P.K. Hopke). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2010.08.022 Atmospheric Environment 45 (2011) 7672e7680