Molecular composition and volatility of secondary organic compounds from nitrate radical oxidation of biogenic volatile organic compounds – from lab to field

Abstract

Night-time reactions of biogenic volatile organic compounds (BVOCs) and nitrate radicals (NO3) can lead to the formation of secondary organic aerosol (BSOANO3). Here we firstly present the chemical composition and volatility of BSOANO3 formed in the dark from three precursors (isoprene, α-pinene, and β-caryophyllene) in atmospheric simulation chamber experiments (Wu et al., 2021; Bell et al., 2022; Graham et al., 2022). The chemical composition of particle-phase compounds was measured with a chemical ionization mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS) and an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF). The volatility information of BSOANO3 was derived from isothermal evaporation chambers, temperature-dependent evaporation in a volatility tandem differential mobility analyzer (VTDMA), and thermal desorption in the FIGAERO-CIMS. In addition, the molecular composition of particulate compounds was used in volatility parametrizations to calculate the compounds’ saturation vapor pressures and to establish volatility basis sets (VBS, Donahue et al., 2011) for the bulk aerosol. Four different parametrizations were tested for reproducing the observed evaporation in a kinetic modeling framework (Riipinen et al., 2010). Here, we compare the different methods for particle volatility determination and discuss the limitation of the parameterizations.Our results suggest the BSOANO3 from α-pinene and isoprene be dominated by low-volatility organic compounds (LVOC) and semi-volatile organic compounds (SVOC), while the corresponding BSOANO3 from β-caryophyllene consists primarily of extremely low-volatility organic compounds (ELVOC) and LVOC. The parameterizations yielded variable results in terms of reproducing the observed evaporation, and generally the comparisons pointed to a need for re-evaluating the treatment of the nitrate group in such parameterizations.Furthermore, we link the lab experiments to field observations of secondary organic aerosols and organic nitrates from a boreal forest (ICOS Norunda, Sweden), which is dominated by monoterpene emissions and includes also isoprene and sesquiterpene emissions. We will show the chemical composition and volatility of the particles detected with a FIGAERO-CIMS, compare them to the lab results, and discuss how nitrate-initiated nighttime oxidation of different precursors contribute to the total particle formation and growth.