The influence of cloud chemistry on HOx and NOx in the moderately polluted marine boundary layer: a 1-D modelling study

A 1-D marine stratocumulus cloud model has been supplemented with a comprehensive and up-to-date aqueous phase chemical mechanism for the purpose of assessing the impact that the presence of clouds has on gas phase HOx, NOx and O-3 budgets in the marine boundary layer. The simulations presented here indicate that cloud may act as a heterogeneous source of HONOg. The conversion of HNO4(g) at moderate pH (similar to4.5) is responsible for this, and, to a lesser extent, the photolysis of nitrate (NO3-). The effect of introducing deliquescent aerosol on the simulated increase of HONOg is negligible. The most important consequences of this elevation in HONOg are that, in the presence of cloud, gas phase concentrations of NOx species increase by a factor of 2, which minimises the simulated decrease in O-3(g), and results in a regeneration of OHg. This partly compensates for the removal of OHg by direct phasetransfer into the cloud and may have important implications regarding the oxidising capacity of the marine boundary layer.

• View at arXiv