Abstract
Abstract. Particle size distributions in the range of 1.34–615 nm were recorded from 25 November 2013 to 25 January 2014 in urban Shanghai, using a combination of one nano condensation nucleus counter system, one nano scanning mobility particle sizer (SMPS), and one long-SMPS. Measurements of sulfur dioxide by an SO2 analyzer with pulsed UV fluorescence technique allowed calculation of sulfuric acid proxy. In addition, concentrations of ammonia were recorded with a differential optical absorption spectroscopy. During this 62-day campaign, 13 new particle formation (NPF) events were identified with strong bursts of sub-3 nm particles and subsequent fast growth of newly formed particles. The observed nucleation rate (J1.34), formation rate of 3 nm particles (J3), and condensation sink were 112.4–271.0 cm−3 s−1, 2.3–19.2 cm−3 s−1, and 0.030–0.10 s−1, respectively. Subsequent cluster/nanoparticle growth (GR) showed a clear size dependence, with average values of GR1.35~1.39, GR1.39~1.46, GR1.46~1.70, GR1.70~2.39, GR2.39~7, and GR7~20 being 1.6±1.0, 1.4±2.2, 7.2±7.1, 9.0±11.4, 10.9±9.8, and 11.4±9.7 nm h−1, respectively. Correlation between nucleation rate (J1.34) and sulfuric acid proxy indicates that nucleation rate J1.34 was proportional to a 0.65±0.28 power of sulfuric acid proxy, indicating that the nucleation of particles can be explained by the activation theory. Correlation between nucleation rate (J1.34) and gas-phase ammonia suggests that ammonia was associated with NPF events. The calculated sulfuric acid proxy was sufficient to explain the subsequent growth of 1.34–3 nm particles, but its contribution became smaller as the particle size grew. Qualitatively, NPF events in urban Shanghai likely occur on days with low levels of aerosol surface area, meaning the sulfuric acid proxy is only a valid predictor when aerosol surface area is low.
Highlights
Aerosol particles can influence climate directly and indirectly (Andreae and Crutzen, 1997; Haywood and Boucher, 2000; IPCC, 2013), and have adverse impact on human health (Dockery et al, 1993; Laden et al, 2006; Pope and Dockery, 2006)
Progress has been made by the use of a particle size magnifier (PSM) and chemical ionization atmospheric pressure interface timeof-flight mass spectrometer by combining the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber experiments and ambient observations including those in Hyytiälä, Finland, showing that oxidation products of biogenic emissions, together with sulfuric acid, contribute to new particle formation in the atmosphere (Schobesberger et al, 2013; Riccobono et al, 2014)
A new particle formation (NPF) day will present a banana-shaped contour plot of particle size distributions obtained from scanning mobility particle sizer (SMPS) (Dal Maso et al, 2005)
Summary
Aerosol particles can influence climate directly and indirectly (Andreae and Crutzen, 1997; Haywood and Boucher, 2000; IPCC, 2013), and have adverse impact on human health (Dockery et al, 1993; Laden et al, 2006; Pope and Dockery, 2006). Atmospheric nucleation of gas-phase precursors to clusters and further to nanoparticles is the largest source of atmospheric aerosol particles (Kulmala et al, 2004b; Zhang et al, 2012). This phenomenon has been observed in numerous locations around the world, including areas with a pristine atmosphere, e.g., coastal areas (O’Dowd et al, 2002), Antarctic/Arctic (Park et al, 2004), remote forest (Dal Maso et al, 2005), semi-rural locations with very low pollution levels such as Kent, OH (Kanawade et al, 2012), and heavily polluted cities, such as Mexico City (Dunn et al, 2004). The potential nucleation mechanism was explored by correlating sulfuric acid proxy calculated from sulfur dioxide precursor and gas-phase ammonia to nucleation rate J1.34
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