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Assessing the importance of nitric acid and ammonia for particle growth in the polluted boundary layer.

ABSTRACT: Aerosols formed and grown by gas-to-particle processes are a major contributor to smog and haze in megacities, despite the competition between growth and loss rates. Rapid growth rates from ammonium nitrate formation have the potential to sustain particle number in typical urban polluted conditions. This process requires supersaturation of gas-phase ammonia and nitric acid with respect to ammonium nitrate saturation ratios. Urban environments are inhomogeneous. In the troposphere, vertical mixing is fast, and aerosols may experience rapidly changing temperatures. In areas close to sources of pollution, gas-phase concentrations can also be highly variable. In this work we present results from nucleation experiments at -10 °C and 5 °C in the CLOUD chamber at CERN. We verify, using a kinetic model, how long supersaturation is likely to be sustained under urban conditions with temperature and concentration inhomogeneities, and the impact it may have on the particle size distribution. We show that rapid and strong temperature changes of 1 °C min^-1 are needed to cause rapid growth of nanoparticles through ammonium nitrate formation. Furthermore, inhomogeneous emissions of ammonia in cities may also cause rapid growth of particles.

SUBMITTER: Marten R

PROVIDER: S-EPMC10867809 | biostudies-literature | 2024 Feb

REPOSITORIES: biostudies-literature

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Assessing the importance of nitric acid and ammonia for particle growth in the polluted boundary layer.

Marten Ruby R Xiao Mao M Wang Mingyi M Kong Weimeng W He Xu-Cheng XC Stolzenburg Dominik D Pfeifer Joschka J Marie Guillaume G Wang Dongyu S DS Elser Miriam M Baccarini Andrea A Lee Chuan Ping CP Amorim Antonio A Baalbaki Rima R Bell David M DM Bertozzi Barbara B Caudillo Lucía L Dada Lubna L Duplissy Jonathan J Finkenzeller Henning H Heinritzi Martin M Lampimäki Markus M Lehtipalo Katrianne K Manninen Hanna E HE Mentler Bernhard B Onnela Antti A Petäjä Tuukka T Philippov Maxim M Rörup Birte B Scholz Wiebke W Shen Jiali J Tham Yee Jun YJ Tomé António A Wagner Andrea C AC Weber Stefan K SK Zauner-Wieczorek Marcel M Curtius Joachim J Kulmala Markku M Volkamer Rainer R Worsnop Douglas R DR Dommen Josef J Flagan Richard C RC Kirkby Jasper J McPherson Donahue Neil N Lamkaddam Houssni H Baltensperger Urs U El Haddad Imad I

Environmental science: atmospheres 20240125 2

Aerosols formed and grown by gas-to-particle processes are a major contributor to smog and haze in megacities, despite the competition between growth and loss rates. Rapid growth rates from ammonium nitrate formation have the potential to sustain particle number in typical urban polluted conditions. This process requires supersaturation of gas-phase ammonia and nitric acid with respect to ammonium nitrate saturation ratios. Urban environments are inhomogeneous. In the troposphere, vertical mixin ...[more]

PMID: 38371605

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Project description:A list of authors and their affiliations appears at the end of the paper New-particle formation is a major contributor to urban smog1,2, but how it occurs in cities is often puzzling3. If the growth rates of urban particles are similar to those found in cleaner environments (1-10 nanometres per hour), then existing understanding suggests that new urban particles should be rapidly scavenged by the high concentration of pre-existing particles. Here we show, through experiments performed under atmospheric conditions in the CLOUD chamber at CERN, that below about +5 degrees Celsius, nitric acid and ammonia vapours can condense onto freshly nucleated particles as small as a few nanometres in diameter. Moreover, when it is cold enough (below -15 degrees Celsius), nitric acid and ammonia can nucleate directly through an acid-base stabilization mechanism to form ammonium nitrate particles. Given that these vapours are often one thousand times more abundant than sulfuric acid, the resulting particle growth rates can be extremely high, reaching well above 100 nanometres per hour. However, these high growth rates require the gas-particle ammonium nitrate system to be out of equilibrium in order to sustain gas-phase supersaturations. In view of the strong temperature dependence that we measure for the gas-phase supersaturations, we expect such transient conditions to occur in inhomogeneous urban settings, especially in wintertime, driven by vertical mixing and by strong local sources such as traffic. Even though rapid growth from nitric acid and ammonia condensation may last for only a few minutes, it is nonetheless fast enough to shepherd freshly nucleated particles through the smallest size range where they are most vulnerable to scavenging loss, thus greatly increasing their survival probability. We also expect nitric acid and ammonia nucleation and rapid growth to be important in the relatively clean and cold upper free troposphere, where ammonia can be convected from the continental boundary layer and nitric acid is abundant from electrical storms4,5.

Dataset Information

Assessing the importance of nitric acid and ammonia for particle growth in the polluted boundary layer.

Publications

Assessing the importance of nitric acid and ammonia for particle growth in the polluted boundary layer.

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