The influence of cloud chemistry on HOx and NOx in the moderately polluted marine boundary layer: a 1-D modelling study J. E. Williams1,2, F. J. Dentener3, and A. R. van den Berg1 1IMAU, University of Utrecht, Utrecht, The Netherlands 2Current Address: FOM-AMOLF, Kruislaan 107, Amsterdam, The Netherlands 3Joint Research Center, Environment Institute, Ispra(Va), Italy
Abstract. 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 phaseHOx, NOx and O3 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 (~ 4.5) 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
O3(g), and results in a regeneration of OHg. This partly compensates
for the removal of OHg by direct phase transfer into the cloud and may have important implications regarding the oxidising
capacity of the marine boundary layer.
Citation: Williams, J. E., Dentener, F. J., and van den Berg, A. R.: The influence of cloud chemistry on HOx and NOx in the moderately polluted marine boundary layer: a 1-D modelling study, Atmos. Chem. Phys., 2, 39-54, doi:10.5194/acp-2-39-2002, 2002.