10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Investigation of Multicomponent New Particle Formation under Urban Atmospheric Conditions in the CLOUD Chamber
MAO XIAO, Christopher R. Hoyle, Lubna Dada, Mingyi Wang, Dominik Stolzenburg, Lukas Fischer, Andrea Baccarini, Chuan Ping Lee, Houssni Lamkaddam, Ruby Marten, Imad EI Haddad, Josef Dommen, Urs Baltensperger, CLOUD Collaboration, Paul Scherrer Institute
Abstract Number: 941 Working Group: Aerosol Chemistry
Abstract The formation of new particles from atmospheric vapors (new particle formation, NPF) is an important atmospheric process having great effects on the particle number concentration and size distributions. Urban atmospheres are highly polluted with high concentrations of sulfuric acid, ammonia, NOx and volatile organic gases primarily emitted from anthropogenic activities. Despite the high particle concentrations in polluted air, which are unfavorable for NPF, NPF is still reported to occur with high frequency and at high formation rates in highly-polluted urban environments.
Photochemical air pollution in the urban atmosphere is often dominated by anthropogenic volatile organic compounds, containing a high fraction of aromatic hydrocarbons originating from industrial activities, traffic and residential wood combustion. Observations of highly oxygenated molecules forming in OH-triggered oxidation of aromatic hydrocarbons (Molteni et al., 2018; Wang et al., 2017) suggest that aromatics could be potential precursors for NPF especially in the polluted atmosphere. Another potential class of compounds participating in NPF in a polluted atmosphere is amines. Amines in urban air may enable high formation rates under atmospherically relevant sulfuric acid concentrations. Amine enhancement of NPF is known from earlier chamber studies (Almeida et al., 2013), but this effect was believed to be only significant when it is close to the amine sources due to the short life-times of gaseous amines.
To investigate the role of amines and aromatic hydrocarbons in NPF under polluted urban atmospheric conditions, experiments were conducted at the “Cosmics Leaving OUtdoor Droplets” (CLOUD) facility at the European Organization for Nuclear Research (CERN). New particle formation from the mixtures of naphthalene, 1,2,4- trimethylbenzene and toluene, sulfuric acid and ammonia in the presence of NOx were studied with and without the addition of 0.4 ppt dimethylamine at 278 K and 293 K. New particle formation rates and early growth rates calculated for each temperature. New particle formation rates and early growth rates derived for each temperature as well as the enhancement with the addition of dimethylamine will be reported. Low temperature favors NPF both with and without dimethylamine addition. The contribution of sulfuric acid, nitric acid and organics to sub-3 nm particle growth is also evaluated based on particle composition measurements.
The research is supported by the Swiss National Science Foundation and the MSCA-ITN project CLOUD-MOTION no. 764991. We thank CERN for supporting CLOUD with important technical and financial resources, and for providing a particle beam from the Proton Synchrotron. We acknowledge tofTools software for mass spectrometry analysis.
[1] Almeida, J., et al. (2013) Nature 502(7471), 359-363. [2] Molteni, U., et al. (2018) Atmos. Chem. Phys., in press. [3] Wang, S., et al. (2017) Environ. Sci. Tech., 51(15), 8442-8449.