Abstract
Abstract. New particle formation (NPF) is a significant source of atmospheric particles, affecting climate and air quality. Understanding the mechanisms involved in urban aerosols is important to develop effective mitigation strategies. However, NPF rates reported in the polluted boundary layer span more than 4 orders of magnitude, and the reasons behind this variability are the subject of intense scientific debate. Multiple atmospheric vapours have been postulated to participate in NPF, including sulfuric acid, ammonia, amines and organics, but their relative roles remain unclear. We investigated NPF in the CLOUD chamber using mixtures of anthropogenic vapours that simulate polluted boundary layer conditions. We demonstrate that NPF in polluted environments is largely driven by the formation of sulfuric acid–base clusters, stabilized by the presence of amines, high ammonia concentrations and lower temperatures. Aromatic oxidation products, despite their extremely low volatility, play a minor role in NPF in the chosen urban environment but can be important for particle growth and hence for the survival of newly formed particles. Our measurements quantitatively account for NPF in highly diverse urban environments and explain its large observed variability. Such quantitative information obtained under controlled laboratory conditions will help the interpretation of future ambient observations of NPF rates in polluted atmospheres.
Highlights
New particle formation (NPF) is an important atmospheric phenomenon, affecting both climate (Dunne et al, 2016) and air quality (Guo et al, 2014)
We investigated a complex mixture of H2SO4, ammonia, dimethylamine (DMA), NOx, ozone, water and several anthropogenic volatile organic compounds (AVOCs: naphthalene (NAPH), 1,2,4trimethylbenzene (TMB) and toluene (TOL)), at different temperatures
NPF rates in the atmosphere often exhibit a clear correlation with H2SO4 (Kuang et al, 2008; Paasonen et al, 2010; Yao et al, 2018), but chamber experiments show that H2SO4 and water alone cannot explain boundary layer NPF events (Kirkby et al, 2011)
Summary
New particle formation (NPF) is an important atmospheric phenomenon, affecting both climate (Dunne et al, 2016) and air quality (Guo et al, 2014). In Barcelona, Brean et al (2020) linked nucleation to sulfuric acid clustering with both highly oxygenated organic molecules (HOMs) and bases, while Guo et al (2020) argued photooxidation of organics from vehicular exhaust is responsible for the formation of ultrafine particles in Beijing. These conflicting observations and interpretations highlight the need to better understand the role of the different vapours and environmental parameters and to quantify their relative contribution in new particle formation and growth in different polluted locations
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