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

F Salimi,G Johnson,C He,Z Ristovski,L R Crilley,S Stevanovic,M Mazaheri,G Ayoko,L Morawska

doi:10.5194/acp-15-13475-2015

Abstract

Abstract. 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 f43, f44 and f57, were calculated and the f44 vs. f43 trends were compared between nucleation and non-nucleation days. K-means cluster analysis was performed on f44 vs. f43 data and it was found that they follow different patterns on nucleation days compared to non-nucleation days, whereby f43 decreased for vehicle-emission-generated particles, while both f44 and f43 decreased for NPF-generated particles. It was found for the first time that vehicle-generated and newly formed particles cluster in different locations on f44 vs. f43 plot, and this finding can be potentially used as a tool for source apportionment of measured particles.

Highlights

Aerosol particles affect the Earth’s climate, air quality and public health, both directly and indirectly (e.g. Stevens and Feingold, 2009; Lohmann and Feichter, 2005; Pope II and Dockery, 2006)
New particle formation (NPF; known as nucleation) events have been observed in different locations, including coastal, forested, rural and urban areas (O’Dowd et al, 2002; Kulmala et al, 2007; Petäjä et al, 2007; Stanier et al, 2004; Woo et al, 2001;S alma et al, 2010; Cheung et al, 2010; Mejía and Morawska, 2009; Modini et al, 2009), and these events are one of the main sources of ultrafine particles (UFPs; particles smaller than 100 nm), in addition to combustion-emitted particles (Morawska et al, 2009)
Solar radiation and other meteorological parameters were measured by a Monitor Sensors μ Smart Series weather station, a TSI 3781 water-based Condensation Particle Counter (CPC) was used for particle number concentration (PNC) measurements, and a TSI DustTrak measured particle mass concentration (PM2.5 and PM10)

Summary

Introduction

Aerosol particles affect the Earth’s climate, air quality and public health, both directly and indirectly (e.g. Stevens and Feingold, 2009; Lohmann and Feichter, 2005; Pope II and Dockery, 2006). Stevens and Feingold, 2009; Lohmann and Feichter, 2005; Pope II and Dockery, 2006). Aerosol particles affect the Earth’s climate, air quality and public health, both directly and indirectly Knowledge about their formation, transformation and physical/chemical properties helps in understanding their effects on climate and human health. Salimi et al.: Insights into the growth of newly formed particles tality and morbidity (Donaldson et al, 2002; WHO, 2005; Ning et al, 2003)

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