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 phases, 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 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 4 orders of magnitude higher on average than
the theoretical value (KPt, 2.8×10-7 m3 µg−1) at 270±4 K. Beyond following Henry's law or Pankow's
absorptive partitioning theory, the partitioning of H2O2 in the
gas-liquid and gas-aerosol phases in the ambient atmosphere was 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 69 % of the collected rain samples, the
measured level of H2O2 was greater than the predicted value in
pure water calculated by Henry's law. In these samples, 41 % of the
measured H2O2 was from gas-phase partitioning, while most of the
rest may be 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. The contribution of partitioning of the gas-phase
H2O2 to the aerosol-phase H2O2 formation was negligible.
The decomposition/hydrolysis rate of aerosol-phase organic peroxides could
account for 11 %–74 % of the consumption rate of aerosol-phase
H2O2, and the value depended on the composition of organic
peroxides in the aerosol particles. Furthermore, the heterogeneous uptake of
HO2 and H2O2 on aerosols contributed to 22 % and 2 %
of the aerosol-phase H2O2 consumption, respectively.
Effect of textual features and surface properties of activated carbon on the production of hydrogen peroxide from hydroxylamine oxidation