Investigation into chemistry of new particle formation and growth in subtropical urban environment

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 chemistry 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 and PNSD, respectively. Five NPF events, with growth rates in the range 3.3–4.6 nm, were detected at two sites. The NPF events happened on relatively warmer days with lower humidity and higher solar radiation. Temporal percent fractions of nitrate, sulphate, ammonium and organics were modelled using the Generalised Additive Model (GAM), with a basis of penalised spline. Percent fractions of organics increased after the NPF events, while the mass fraction of ammonium and sulphate decreased. This uncovered the important role of organics in the growth of newly formed particles. Three organic markers, factors f 43, f 44 and f 57, were calculated and the f 44 vs. f 43 trends were compared between nucleation and non-nucleation days. f 44 vs. f 43 followed a different pattern on nucleation days compared to non-nucleation days, whereby f 43 decreased for vehicle emission generated particles, while both f 44 and f 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 f 44 vs. f 43 plot and this finding can be used as a~tool for source apportionment of measured particles.