Insights into the growth of newly formed particles in a subtropical urban environment

• Main Authors: F. Salimi, L. R. Crilley, S. Stevanovic, Z. Ristovski, M. Mazaheri, C. He, G. Johnson, G. Ayoko, L. Morawska
• Format: Article
• Language: English
• Published: Copernicus Publications 2015-12-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/15/13475/2015/acp-15-13475-2015.pdf

The role of different chemical compounds, particularly organics, involved in the new particle formation (NPF) and its consequent growth are not fully understood. Therefore, this study was conducted to investigate the chemical composition of aerosol particles during NPF events in an urban subtropical environment. Aerosol chemical composition was measured along with particle number size distribution (PNSD) and several other air quality parameters at five sites across an urban subtropical environment. An Aerodyne compact Time-of-Flight Aerosol Mass Spectrometer (c-ToF-AMS) and a TSI Scanning Mobility Particle Sizer (SMPS) measured aerosol chemical composition (particles above 50 nm in vacuum aerodynamic diameter) and PNSD (particles within 9–414 nm in mobility diameter), respectively. Five NPF events, with growth rates in the range 3.3–4.6 nm, were detected at two of the sites. The NPF events happened on relatively warmer days with lower condensation sink (CS). Temporal percent fractions of organics increased after the particles grew enough to have a significant contribution to particle volume, while the mass fraction of ammonium and sulfate decreased. This uncovered the important role of organics in the growth of newly formed particles. Three organic markers, factors <i>f</i>₄₃, <i>f</i>₄₄ and <i>f</i>₅₇, were calculated and the <i>f</i>₄₄ vs. <i>f</i>₄₃ trends were compared between nucleation and non-nucleation days. K-means cluster analysis was performed on <i>f</i>₄₄ vs. <i>f</i>₄₃ data and it was found that they follow different patterns on nucleation days compared to non-nucleation days, whereby <i>f</i>₄₃ decreased for vehicle-emission-generated particles, while both <i>f</i>₄₄ and <i>f</i>₄₃ decreased for NPF-generated particles. It was found for the first time that vehicle-generated and newly formed particles cluster in different locations on <i>f</i>₄₄ vs. <i>f</i>₄₃ plot, and this finding can be potentially used as a tool for source apportionment of measured particles.