US EPA

3843064 

Journal Article 

Effect of nitrogen oxides (NO and NO2) and toluene on SO2 photooxidation, nucleation and growth: A smog chamber study 

Li, K; Chen, L; White, SJ; Han, Ke; Lv, B; Bao, K; Wu, X; Gao, X; Azzi, M; Cen, K 

2017 

Yes 

Atmospheric Research
ISSN: 0169-8095
EISSN: 1873-2895 

192 

38-47 

10.1016/j.atmosres.2017.03.017 

WOS:000401885000005 

The formation and growth of new particles has recently been shown to have a significant influence on Chinese haze pollution, and sulfuric acid has long been recognized as a major contributor to new particle formation. In this study, four comparison groups of experiments related to SO2 photooxidation, as well as aerosol nucleation and growth, have been conducted in the CAPS-ZJU (Complex Air Pollution Study-Zhejiang University) smog chamber. These were conducted either under SO2/NOx or SO2/toluene gas-phase environments in the absence of seed particles. During aerosol nucleation and growth process, several physical properties such as mass, size and effective density were measured simultaneously by Scanning Mobility Particle Sizer (SMPS) and Differential Mobility Analyzer-Aerosol Particle Mass Analyzer-Condensation Particle Counter (DMA-APM-CPC). The effective density of new particles decreased from 1.8 to 135 g/cm(3) as the particle size increased from 20 to 65 nm. The single particle mass showed good power-law relationship with mobility diameter, with an average mass-mobility exponent of 2.885. A new algorithm and a reference density of 138 g/cm3 based on size-resolved single particle mass (SPM) were proposed to calculate the mass concentration of new particles. Two methods based on Log Normal and Max Concentration were applied to derive particle growth rate (GR), and data merging from both methods was implemented to decrease calculation uncertainty. Meanwhile, both continuous nucleation and inhibition of further growth in sub-20 nm size range were observed in different experiments depending on composition, and possible reasons were analyzed. The presence of NO was found to suppress nucleation and subsequent aerosol growth; while the presence of NO2. or toluene promoted it. It was concluded that decreasing NOx (NO or NO2) or increasing toluene may promote SO2 photooxidation, nucleation and subsequent aerosol growth, all of which is significant for deeper understanding of complex air pollution in China. (C) 2017 Elsevier B.V. All rights reserved. 

Smog chamber; New particle formation; Complex air pollution; Effective density; PM2.5