摘要:

Hydrogen peroxide (H₂O₂) and organic peroxides play important roles in the cycle of oxidants and the formation of secondary aerosols in the atmosphere. Recent field observations have suggested that the budget of peroxyacetic acid (PAA, CH₃C(O)OOH) is potentially related to the aerosol phase processes, especially to secondary aerosol formation. Here, we present the first laboratory measurements of the uptake coefficient of gaseous PAA and H₂O₂ onto ambient fine particulate matter (PM_2.5) as a function of relative humidity (RH) at 298 K. The results show that the PM_2.5, which was collected in an urban area, can take up PAA and H₂O₂ at the uptake coefficient (r) of 10^-4, and bothg r_PAA and r_H2O2 increase with increasing RH. The value of r_PAA at 90%RH is 5.4±1.9 times that at 3%RH, whereas r_H2O2 at 90%RH is 2.4±0.5 times that at 3%RH, which suggests that PAA is more sensitive to the RH variation than H₂O₂ is. Considering the larger Henry’s law constant of H₂O₂ than that of PAA, the smaller RH sensitivity of the H₂O₂ uptake coefficient suggests that the enhanced uptake of peroxide compounds on PM_2.5 under humid conditions is dominated by chemical processes rather than dissolution. Considering that mineral dust is one of the main components of PM_2.5 in Beijing, we also determined the uptake coefficients of gaseous PAA and H₂O₂ on authentic Asian Dust storm (ADS) and Arizona Test Dust (ATD) particles. Compared to ambient PM_2.5, ADS shows a similar value and RH dependence in its uptake coefficient for PAA and H₂O₂, while ATD gives a negative dependence on RH. The present study indicates that, in addition to the mineral dust in PM_2.5, other components (e.g., soluble inorganic salts) are also important to the uptake of peroxide compounds. When the heterogeneous reaction of PAA on PM_2.5 is considered, its atmospheric lifetime is estimated to be 3.0 h on haze days and 7.1 h on non-haze days, values that are in good agreement with the field observations.