Abstract. Hydrogen peroxide (H2O2) is a vital oxidant in the atmosphere and plays critical roles in the oxidation chemistry of both liquid and aerosol phases. The partitioning of H2O2 between the gas and liquid phase or the aerosol phase could affect its abundance in these condensed phases and eventually the formation of secondary components. However, the partitioning processes of H2O2 in gas-liquid and gas-aerosol phases are still unclear, especially in the ambient atmosphere. In this study, field observations of gas-, liquid-, and aerosol-phase H2O2 were carried out in the urban atmosphere of Beijing during the summer and winter of 2018. The effective field-derived mean value of Henry's law constant (HAm, 2.1 × 105 M atm−1) was 2.5 times that of the theoretical value in pure water (HAt, 8.4 × 104 M atm−1) at 298 ± 2 K. The effective derived gas-aerosol partitioning coefficient (KPm, 3.8 × 10−3 m3 μg−1) was four orders of magnitude higher on average than the theoretical value (KPt, 2.8 × 10−7 M atm−1) at 270 ± 4 K. The partitioning of H2O2 in the gas-liquid and gas-aerosol phases in the ambient atmosphere does not only obey Henry's law or Pankow's absorptive partitioning theory but is also influenced by certain physical and chemical reactions. The average concentration of liquid-phase H2O2 in rainwater during summer was 44.12 ± 26.49 μM. In three-quarters of the collected rain samples, the measured H2O2 was greater than the predicted value in pure water calculated by Henry's law. In these samples, 46 % of the measured H2O2 was from gas-phase partitioning, and most of the rest may have come from residual H2O2 in raindrops. In winter, the level of aerosol-phase H2O2 was 0.093 ± 0.085 ng μg−1, which was much higher than the predicted value based on Pankow's absorptive partitioning theory. Almost all aerosol-phase H2O2 was not from the partitioning of the gas phase. The decomposition/hydrolysis of aerosol-phase organic peroxides could be responsible for 32 % of aerosol-phase H2O2 formation at the maximum rate of 3.65 ng μg−1. Furthermore, the heterogeneous uptake of H2O2 on aerosols contributed to less than 0.5 %.
Correction to “Henry's law determinations for aqueous solutions of hydrogen peroxide, methylhydroperoxide, and peroxyacetic acid” by John A. Lind and Gregory L. Kok