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[AAS11-P11] Measurement of uptake coefficient of organic peroxyl radical derived from propene onto NaCl particles by LIF technique
Keywords:peroxyl radical, uptake coefficient, LP-LIF
Tropospheric ozone is the main component of photochemical oxidant generated through photolysis procedure with the existence of volatile organic compounds (VOCs) and NOx (= NO+NO2) as precursors. In Japan, although the precursors have been decreased, ozone has been gradually increasing since 1980’s. Reduction of aerosols associated with air quality improvement would contribute to such ozone trend since the aerosol reduction suppresses heterogeneous loss by aerosol uptake of radicals involved in the ozone generation (HOX = OH, HO2 and RO2), which makes ozone generation more efficiently. Uptake coefficient (γ) is a reactional kinetic parameter and is required to quantitatively assess this ozone suppressing effect by aerosols. To date, many studies have been conducted on measurement of γ of hydroxy radical (OH) and hydroperoxyl radical (HO2). However, γ measurement method for organic peroxyl radicals (RO2) hasn’t been still established due to difficulty in the experiment. Consequently, there are few γ measurement works. Moreover, no γ reports of RO2 with a hydroxy group (R(OH)O2) are available.
With the aim of establishing the measurement method of γ for R(OH)O2 radicals, this work applied the laser-pumped and laser-induced fluorescence (LP-LIF) technique (Sadanaga et al., 2004) for measurement of γ for propene derived CH3CH(OO)CH2OH onto NaCl particles. γ was determined from the decay rate of radicals measured by LP-LIF and aerosol surface concentration measured by scanning mobility particle sizer (SMPS). Particles were generated by nebulizing NaCl solution and directly measured as aqueous particles at 85% RH. We prepared three types of particles: pure (None), CuCl2 (as a transition metal ion)-doped and ascorbic acid (AA, as an antioxidant)-doped NaCl particles. We validated our experimental system by conducting measurement of γ of HO2 and by confirming that our results showed good agreement with literature value (Taketani et al., 2008).
In summary, we determined γ of CH3CH(OO)CH2OH onto pure NaCl, onto CuCl2 doped and onto ascorbic acid doped particles to be γNone=0.04±0.01, γCuCl2=0.04±0.01, and γAA=0.24±0.04, respectively. These results have shown that γ onto CuCl2 doped NaCl particles isn’t changed from γ onto pure ones, on the other hand, γ onto ascorbic acid doped ones becomes several times larger than the others. These γ values are the first experimental reports as R(OH)O2 radicals’ γ and thus no references are available.
Our result suggests that γ of R(OH)O2 onto wet particles are possibly in the range of 0.04~0.24 in the troposphere, which includes the recommended value, γ =0.1 (Jacob, 2000). However, at the same time, our results indicates that the recommended value has a large uncertainty. It is required to conduct further experiments using other types of RO2 radicals and standard aerosols, and with ambient particles.
Jacob, D. J. (2000). Heterogeneous chemistry and tropospheric ozone. Atmos. Environ., 34, 2131-2159.
Kohno, N., et al. (2021). Rate constants of CH3O2 + NO2 ⇔ CH3O2NO2 and C2H5O2 + NO2 ⇔ C2H5O2NO2 reactions under atmospheric conditions. Int. J. Chem. Kinet., 53, 571-582.
Sadanaga, Y., et al. (2004). Development of a measurement system of OH reactivity in the atmosphere by using a laser-induced pump and probe technique. Rev. Sci. Instrum., 75(8), 2648-2655.
Taketani, F., et al. (2008). Kinetics of Heterogeneous Reactions of HO2 Radical at Ambient Concentration Levels with (NH4)2SO4 and NaCl Aerosol Particles. J. Phys. Chem. A, 112(11), 2370–2377.
With the aim of establishing the measurement method of γ for R(OH)O2 radicals, this work applied the laser-pumped and laser-induced fluorescence (LP-LIF) technique (Sadanaga et al., 2004) for measurement of γ for propene derived CH3CH(OO)CH2OH onto NaCl particles. γ was determined from the decay rate of radicals measured by LP-LIF and aerosol surface concentration measured by scanning mobility particle sizer (SMPS). Particles were generated by nebulizing NaCl solution and directly measured as aqueous particles at 85% RH. We prepared three types of particles: pure (None), CuCl2 (as a transition metal ion)-doped and ascorbic acid (AA, as an antioxidant)-doped NaCl particles. We validated our experimental system by conducting measurement of γ of HO2 and by confirming that our results showed good agreement with literature value (Taketani et al., 2008).
In summary, we determined γ of CH3CH(OO)CH2OH onto pure NaCl, onto CuCl2 doped and onto ascorbic acid doped particles to be γNone=0.04±0.01, γCuCl2=0.04±0.01, and γAA=0.24±0.04, respectively. These results have shown that γ onto CuCl2 doped NaCl particles isn’t changed from γ onto pure ones, on the other hand, γ onto ascorbic acid doped ones becomes several times larger than the others. These γ values are the first experimental reports as R(OH)O2 radicals’ γ and thus no references are available.
Our result suggests that γ of R(OH)O2 onto wet particles are possibly in the range of 0.04~0.24 in the troposphere, which includes the recommended value, γ =0.1 (Jacob, 2000). However, at the same time, our results indicates that the recommended value has a large uncertainty. It is required to conduct further experiments using other types of RO2 radicals and standard aerosols, and with ambient particles.
Jacob, D. J. (2000). Heterogeneous chemistry and tropospheric ozone. Atmos. Environ., 34, 2131-2159.
Kohno, N., et al. (2021). Rate constants of CH3O2 + NO2 ⇔ CH3O2NO2 and C2H5O2 + NO2 ⇔ C2H5O2NO2 reactions under atmospheric conditions. Int. J. Chem. Kinet., 53, 571-582.
Sadanaga, Y., et al. (2004). Development of a measurement system of OH reactivity in the atmosphere by using a laser-induced pump and probe technique. Rev. Sci. Instrum., 75(8), 2648-2655.
Taketani, F., et al. (2008). Kinetics of Heterogeneous Reactions of HO2 Radical at Ambient Concentration Levels with (NH4)2SO4 and NaCl Aerosol Particles. J. Phys. Chem. A, 112(11), 2370–2377.