UC San Diego

Organic nitrates, produced from the oxidation of biogenic volatile organic compounds (BVOC) in the presence of nitrogen oxides (NOx), have significant contributions to the global secondary organic aerosol (SOA) budget and slow the production of ozone by sequestering NOx. Monoterpenes, such as α-pinene, are important organic nitrate and SOA precursors and are the second largest contributor to non-methane BVOC mass next to isoprene. It has been observed in previous studies that α-pinene-derived hyrdroxy nitrates readily partition to the particle phase, introducing a potential sink for atmospheric NOx through reactions such as acid-catalyzed hydrolysis. However, the role of relative humidity and particle acidity in the mass accommodation and rate of uptake of hydroxy nitrates by aerosol are not well understood, introducing a knowledge gap in the fate of atmospheric NOx. In this experiment, an α-pinene hydroxy nitrate is synthesized and introduced to a potential mass aerosol oxidation flow reactor (PAM-OFR) with dry, zero air flowed through a temperature controlled glass tube to elucidate the uptake rates of α-pinene hydroxy nitrate in the presence of ammonium sulfate seed aerosol. α-pinene hydroxy nitrate uptake kinetics are determined via analysis of hydroxy nitrate concentrations in the gas phase using a high-resolution time-of-flight chemical ionization mass spectrometer (HR-TOF-CIMS). Our results will report on the uptake kinetics of this hydroxy nitrate as a function of relative humidity and seed particle acidity and may provide new insight into the timescales at which α-pinene derived organic nitrates partition to the particle phase, offering more detailed considerations for future modeling studies.