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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  14 May 2020

14 May 2020

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This preprint is currently under review for the journal ACP.

Direct contribution of ammonia to CCN-size alpha-pinene secondary organic aerosol formation

Liqing Hao1, Eetu Kari1,a, Ari Leskinen1,2, Douglas R. Worsnop1,3, and Annele Virtanen1 Liqing Hao et al.
  • 1Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • 2Finnish Meteorological Institute, Kuopio, Finland
  • 3Aerodyne Research Inc., Billerica, MA 08121-3976, USA
  • anow at: Neste Oyj, Porvoo, Finland

Abstract. Ammonia (NH3), a gasous compound ubiquitiously present in the atmosphere, is involved in the formation of secondary organic aerosol (SOA), but the exact mechanisum is still not well known. This study presents the results of SOA experiments from the photooxidation of α-pinene in the presence of NH3 in the reaction chamber. SOA was formed in nucleation experiment and in seeded experiment with ammonium sulfate particles as seeds. The chemical composition and time-series of compounds in the gas- and particle- phase were characterized by an on-line high-resolution time-of-flight proton transfer reaction mass spectrometer (HR-ToF-PTRMS) and a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), respectively. Our results show that for the aerosol particles in cloud condensation nuclei (CCN) size, the mass concentration of ammonium (NH4+) was still rising even after the mass concentration of organic component started to decrease due to aerosol wall deposition and evaporation, implying the continuous new formation of particle phase ammonium in the process. Stoichiometric neutralization analysis of aerosol indicates that organic acids have a central role in the formation of particle phase ammonium. Our measurements show a good correlation between the gas phase organic mono- and di-carboxylic acids formed in the photooxidation of α-pinene and the ammonium in the particle phase, thus highlighting the contribution of gas-phase organic acids to the ammonium formation in the CCN-size SOA particles. The work shows that the gas-phase organic acids contribute to the SOA formation by forming ammonium salts through acid-base reaction. The changes in aerosol mass, particle size and chemical composition resulting from the NH3-SOA interaction can potentially alter the aerosol direct and indirect forcing and therefore alter its impact on climate change.

Liqing Hao et al.

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Liqing Hao et al.


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Latest update: 29 Sep 2020
Publications Copernicus
Short summary
Our work presents secondary organic aerosol (SOA) formation results in the presence of gaseous ammonia. The particle phase ammonium was continuously produced even after SOA formation has ceased. The gas phase organic acids were experimentally observed to contribute to the formed particle phase ammonium salts. This study suggests that the presence of ammonia may change the mass and chemical composition of large-size SOA particles and can potentially alter the aerosol impact on climate change.
Our work presents secondary organic aerosol (SOA) formation results in the presence of gaseous...