Technical note Oxidation characteristics of airborne carbon nanoparticles by NO 2 Jungbum Choo a , Jae Hee Jung a , Woojin Kim a , Hyuncheol Oh a , Jinho Kim a , Hakjoon Kim b , Yong Jin Kim b , Sangsoo Kim a, ⁎ a School of Mechanical, Aerospace & Systems Engineering, Korea Advanced Institute of Science and Technology, 335 Gwahangno, Yuseong-gu, Daejeon, 305-701, Republic of Korea b Eco-Machinery Research Division, Korea Institute of Machinery & Materials, 171 Jang-dong, Yuseong-gu, Daejeon, 305-343, Republic of Korea ARTICLE DATA ABSTRACT Article history: Received 2 April 2008 Received in revised form 27 June 2008 Accepted 8 July 2008 Available online 30 August 2008 The oxidation characteristics of airborne carbon nanoparticles were investigated at various temperatures and NO 2 concentrations. Airborne carbon nanoparticles were generated by spark-discharging method using nitrogen as a carrier gas. Monodisperse carbon particles classified using a differential mobility analyzer were introduced into a tube furnace with NO 2 for oxidation reaction. The size distributions of oxidized carbon aerosol particles were measured using a scanning mobility particle spectrometer system which consisted of a differential mobility analyzer and a condensation particle counter. The result was that as NO 2 concentrations and reaction temperatures increased, the surface oxidation rate of carbon aerosol particles increased. For NO 2 gas, the activation energy of the oxidation reaction was approximately 76.3 kJ/mol. The activation energy of the oxidation reaction for the mixture of NO 2 and O 2 gases was 65.9 kJ/mol, which is smaller than that for only NO 2 gas. © 2008 Elsevier B.V. All rights reserved. Keywords: Carbon nanoparticle Nitrogen dioxide Surface oxidation rate Activation energy 1. Introduction For over a century, diesel engines have proved reliable, eco- nomical and durable source of power for many applications. Currently, diesel vehicles are undergoing further development due to their higher fuel efficiency and lower CO 2 emissions as compared to gasoline vehicles because regulations concerning diesel vehicles are becoming more severe due to the harmful effects of diesel exhaust on human health and on the environment (Utell and Frampton, 2000; EPA600/8-90/057F, 2002). The particulate matter (PM) from diesel vehicles consists mostly of carbonaceous particle and a volatile organic fraction (VOF). The PM is often formed during combustion process in locally fuel-rich regions and exhausted in the form of solid agglomerates condensed with VOC (Walker, 2004). For diesel engine, the lowering of PM emission is generally based on a filtration system in which trapped PM is periodically removed by means of controlled oxidation reaction with pure O 2 or air. Accordingly, many researchers have investigated the oxidation characteristics of PM exhausted from the diesel engine. Higgins et al. (2002, 2003) investigated the oxidation character- istics of size-selected soot nanoparticles in air with the tempera- ture range of 800–1140 °C. However, according to recent research, NO 2 has been found to be a more efficient oxidant than O 2 at lower temperatures in the range of 200–500 °C (Dorai et al., 2000; Ehrburger et al., 2002; Jeguirim et al., 2005; Kamm et al., 2004). SCIENCE OF THE TOTAL ENVIRONMENT 405 (2008) 396 – 401 ⁎ Corresponding author. Tel.: +82 42 350 2009; fax: +82 42 350 2204. E-mail address: sskim@kaist.ac.kr (S. Kim). 0048-9697/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2008.07.028 available at www.sciencedirect.com www.elsevier.com/locate/scitotenv