Photolytically Induced Changes in Composition and Volatility of Biogenic Secondary Organic Aerosol from Nitrate Radical Oxidation during Night-to-day Transition

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 study the impacts of light exposure on 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. Our study represents BSOANO3 formation conditions where reactions between peroxy radicals (RO2 + RO2) and between RO2 and NO3 are favored. The emphasis here is on the identification of particle-phase organonitrates (ONs) formed in the dark and their changes during photolytic aging on timescales of ~1 h. Chemical composition of particle-phase compounds was measured with a chemical ionization mass spectrometer with filter inlet for gases and aerosols (FIGAERO-CIMS) and an extractive electrospray ionisation time-of-flight mass spectrometer (EESI-TOF). Volatility information of BSOANO3 was derived from FIGAERO-CIMS desorption profiles (thermograms) and a volatility tandem differential mobility analyser (VTDMA). During photolytic aging, there was a relatively small change in mass due to evaporation (