21 Apr 2022
21 Apr 2022
Status: this preprint is currently under review for the journal ACP.

Isothermal evaporation of α-pinene secondary organic aerosol particles formed under low-NOx and high-NOx conditions

Zijun Li1, Angela Buchholz1, Luis M. F. Barreira1,2, Arttu Ylisirniö1, Liqing Hao1, Iida Pullinen1, Siegfried Schobesberger1, and Annele Virtanen1 Zijun Li et al.
  • 1Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • 2Atmospheric Composition Research, Finnish Meteorological Institute, Helsinki, Finland

Abstract. Many recent secondary organic aerosol (SOA) studies mainly focus on biogenic SOA particles formed under low-NOx conditions and thus are applicable to pristine environments with minor anthropogenic influence. Although interactions between biogenic volatile organic compounds and NOx are important in, for instance, suburban areas, there is still a lack of knowledge about volatility and processes controlling the evaporation of biogenic SOA particles formed in the presence of high concentrations of NOx. Here we provide detailed insights into the isothermal evaporation of α-pinene SOA particles that were formed under low-NOx and high-NOx conditions to investigate the evaporation process and the evolution of particle composition during the evaporation in more detail. We coupled Filter Inlet for Gases and AEROsols-Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) measurements of the molecular composition and volatility of the particle phase with isothermal evaporation experiments conducted under a range of relative humidity (RH) conditions from dry to 80 % RH. Very similar changes were observed in particle volatility at any set RH during isothermal evaporation for the α-pinene SOA particles formed under low-NOx and high-NOx conditions. However, there were distinct differences in the initial composition of the two SOA types, possibly due to the influence of NOx on the RO2 chemistry during SOA formation. Such compositional differences consequently impacted the primary type of aqueous-phase processes in each type of SOA particles in the presence of particulate water.

Zijun Li et al.

Status: open (until 04 Jun 2022)

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Zijun Li et al.


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Short summary
Interaction between NOx and biogenic emissions can be important in suburban areas. Our study showed that the addition of NOx during α-pinene SOA formation produced considerable amounts of organic nitrates and affected the composition of non-nitrated organic compounds. The compositional difference consequently altered the primary type of aqueous-phase processes during the isothermal particle evaporation.