The annual cycle of hydrogen peroxide: an indicator of chemical instability?

[摘要] A box model has been used to study the annual cycle inhydrogen peroxide concentrations with the objective of determining whetherthe observed difference in summer and winter values reflects instability inthe underlying photochemistry. The model is run in both steady-state andtime-dependent modes. The steady-state calculations show that, for somerange of NO_x background levels, two stable solutions to the continuityequations exist for a period of days in spring and fall. The correspondingtime-dependent model indicates that, for sufficiently high backgroundNO_x concentrations, the spring and fall changes in H₂O₂concentration may be interpreted as a forced transition between the twounderlying stable regimes. The spring transition is more rapid than that infall, an asymmetry that becomes more marked as background NO_xincreases. This asymmetry is related to the different time scales involvedin chemical production and loss of H₂O₂. Observations of thespring increase in H₂O₂ concentration may therefore provide abetter measure of the change in the underlying chemical regime than does thefall decrease. The model results developed in this paper will be comparedwith two sets of observations that cover annual variations of peroxideconcentrations under different background pollution conditions.

[学科分类] 大气科学