[A-AS11] Atmospheric Chemistry

[AAS11-P01] Physical structure determined for mixed aerosol by aerosol mass spectrometer and Raman microscope and its relationship with hydroperoxy radical uptake coefficient

*Kei Sato¹, Yosuke Sakamoto^1,2, Nanami Emori³, Gen Masao³, Ratih Dwi Fardilah², Jiaru Li², Yoshizumi Kajii^2,1,4 (1.National Institute for Environmental Studies, 2.Kyoto University, 3.Chuo University, 4.Qindao University)

Keywords:Hydrogen oxide radicals, Volatile organic compound, Heterogeneous reaction, Particle phase-state, Environmental chamber

The uptake of HO₂ radicals by aerosol will affect the formation of tropospheric ozone and secondary organic aerosol (SOA). According to observations performed in Yokohama in 2019, the HO₂ uptake coefficient was positively correlated with the fraction of metal composition in atmospheric aerosols and negatively correlated with the fraction of organic composition in atmospheric aerosols. Furthermore, in our previous experimental study combining a chamber and a HO₂ uptake coefficient measurement instrument, it was confirmed that the HO₂ uptake coefficient for copper(II)-containing ammonium sulfate (CuAS) aerosols was ~0.5 at the relative humidity (RH) of ~50%, and that for α-pinene-derived SOA was low (≦0.02) at RH of ~50% and ~80%. The uptake coefficient of SOA/CuAS-mixed aerosols at RH~50% was low (≦0.01) regardless of the order of mixing of the aerosols, and that of mixed aerosols at RH~80% was ~0.2. In this study, to understand the results of mixed aerosols, we investigated the mixing state of aerosols using an aerosol mass spectrometer (AMS) and a Raman microscope. When SOA was generated in the presence of CuAS aerosols, the aerodynamic diameter of the CuAS aerosols measured by AMS increased, and when CuAS aerosols were sprayed in the presence of SOA, the aerodynamic diameter of the SOA also increased; these suggest that internal mixing occurs in both cases. In addition, a particle with a diameter of ~40 μm was collected on a glass plate by volatilizing the solvent from a mixture of an acetone extract of α-pinene-derived SOA and a water extract of CuAS aerosols, and the particle structure in a RH region from 97.5% to 50% was examined by a Raman microscope. At all RH levels, a Raman shift of ~2,900 cm^-1 due to organic compounds was detected at the outermost layer of the particle, and a Raman shift of 976 and 3,143 cm^-1 due to ammonium sulfate was detected at the center of the particle. At RH~50%, the HO₂ uptake coefficient was suppressed due to a high viscosity of the particles; however, at RH~80%, the HO₂ uptake coefficient may increase due to the decrease in the viscosity of the particles.