Molecular insights into new particle formation in Barcelona, Spain

Abstract

Abstract. Atmospheric aerosols contribute some of the greatest uncertainties to estimates of global radiative forcing and have significant effects on human health. New particle formation (NPF) is the process by which new aerosols of sub-2 nm diameter form from gas-phase precursors and contributes significantly to particle numbers in the atmosphere, accounting for approximately 50 % of cloud condensation nuclei globally. Here, we study summertime NPF in urban Barcelona in north-eastern Spain utilising particle counting instruments down to 1.9 nm and a Nitrate Chemical Ionisation Atmospheric Pressure interface Time of Flight Mass Spectrometer (CI-APi-ToF). The rate of formation of new particles is seen to increase linearly with sulfuric acid concentration, although particle formation rates fall short of chamber studies of H2SO4–DMA–H2O while exceeding those of H2SO4–BioOxOrg–H2O nucleation, although a role of highly oxygenated molecules (HOMs) cannot be ruled out. The sulfuric acid dimer : monomer ratio is significantly lower than that seen in experiments involving sulfuric acid and dimethylamine (DMA) in chambers, indicating that stabilisation of sulfuric acid clusters by bases is weaker in this dataset than in chambers, either due to rapid evaporation due to high summertime temperatures or limited pools of stabilising amines. Such a mechanism cannot be verified in these data, as no higher-order H2SO4–amine clusters nor H2SO4–HOM clusters were measured. The high concentrations of HOMs arise from isoprene, alkylbenzene, monoterpene and polycyclic aromatic hydrocarbon (PAH) oxidation, with alkylbenzenes providing greater concentrations of HOMs due to significant local sources. The concentration of these HOMs shows a dependence on temperature. The organic compounds measured primarily fall into the semivolatile organic compound (SVOC) volatility class arising from alkylbenzene and isoprene oxidation. Low-volatility organic compounds (LVOCs) largely arise from oxidation of alkylbenzenes, PAHs and monoterpenes, whereas extremely low-volatility organic compounds (ELVOCs) arise from primarily PAH and monoterpene oxidation. New particle formation without growth past 10 nm is also observed, and on these days oxygenated organic concentrations are lower than on days with growth by a factor of 1.6, and thus high concentrations of low-volatility oxygenated organics which primarily derive from traffic-emitted volatile organic compounds (VOCs) appear to be a necessary condition for the growth of newly formed particles in Barcelona. These results are consistent with prior observations of new particle formation from sulfuric acid–amine reactions in both chambers and the real atmosphere and are likely representative of the urban background of many European Mediterranean cities. A role for HOMs in the nucleation process cannot be confirmed or ruled out, and there is strong circumstantial evidence of the participation of HOMs across multiple volatility classes in particle growth.

The Synergistic Role of Sulfuric Acid, Bases, and Oxidized Organics Governing New‐Particle Formation in Beijing

“…In addition to the high frequency, NPF also occurred with high intensities, with a median J 1.5 of 86 cm −3 s −1 at peak hours (Figure 1a). The high particle formation rates appear to be a common characteristic of NPF in the polluted urban atmosphere, such as Shanghai (Xiao et al, 2015;Yao et al, 2018), Nanjing (Yu et al, 2016), and Barcelona (Brean et al, 2020). These particle formation rates are usually 1-2 orders of magnitude higher than those in relatively clean environments (Kulmala et al, 2013), suggesting the existence of abundant and efficient nucleation species in an urban atmosphere.…”

The driving factors of new particle formation and growth in the polluted boundary layer

“…A custom-made proton transfer time-of-flight mass spectrometer (PTR3) (Breitenlechner et al, 2017) with a core sampling inlet, which transfers sample air through a tripole reaction chamber operated at 80 mbar, was used to measure the TMB and NAPH concentration. A quadrupole proton transfer mass spectrometer (PTR-MS with quadrupole, ION-ICON) measured the toluene concentration in CLOUD11 and a custom-made short TOF proton transfer mass spectrometer was used in CLOUD12 to measure toluene, TMB and naphthalene.…”

Determination of the multiple-scattering correction factor and its cross-sensitivity to scattering and wavelength dependence for different AE33 Aethalometer filter tapes: a multi-instrumental approach

“…Alfaro et al, 2004). Unlike BC, which absorbs radiation in a wide range of wavelengths (from UV to infrared) with a wavelength-independent refractive index, the BrC and mineral dust refractive index increases at shorter wavelengths, close to the UV range (Kirchstetter et al, 2004a;Andreae and Gelencsér, 2006;Bergstrom et al, 2007;Laskin et al, 2015;Cappa et al, 2019). Therefore, having at one's disposal accurate absorption measurement techniques is crucial to determining particles' light absorption which can afterwards be used in climate projections (Mengis and Matthews, 2020;Wang et al, 2020).…”

“…The area of study is characterized by high concentrations of both primary and secondary aerosols, especially in summer (Rodríguez et al, 2002;Dayan et al, 2017;Rivas et al, 2020;Brean et al, 2020) from diverse emission sources. Anthropogenic emissions from road traffic, industry, agriculture and maritime shipping, among others, strongly contribute to the air quality impairment in this region (Querol et al, 2009b;Amato et al, 2009;Pandolfi et al, 2014b).…”