Night-time radical chemistry during the NAMBLEX campaign R. Sommariva1,*, M. J. Pilling1, W. J. Bloss1, D. E. Heard1, J. D. Lee1,**, Z. L. Fleming2, P. S. Monks2, J. M. C. Plane3,***, A. Saiz-Lopez3,****, S. M. Ball4,*****, M. Bitter4, R. L. Jones4, N. Brough3, S. A. Penkett3, J. R. Hopkins5, A. C. Lewis5, and K. A. Read1 1School of Chemistry, University of Leeds, Leeds, UK 2Department of Chemistry, University of Leicester, Leicester, UK 3School of Environmental Sciences, University of East Anglia, Norwich, UK 4University Chemical Laboratory, University of Cambridge, Cambridge, UK 5Department of Chemistry, University of York, York, UK *now at: Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA **now at: Department of Chemistry, University of York, York, UK ***now at: School of Chemistry, University of Leeds, Leeds, UK ****now at: NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA *****now at: Department of Chemistry, University of Leicester, Leicester, UK
Abstract. Night-time chemistry in the Marine Boundary Layer has been modelled
using a number of observationally constrained zero-dimensional
box-models. The models were based upon the Master Chemical Mechanism
(MCM) and the measurements were taken during the North Atlantic
Marine Boundary Layer Experiment (NAMBLEX) campaign at Mace Head,
Ireland in July–September 2002.
The model could reproduce, within the combined uncertainties, the
measured concentration of HO2 (within 30–40%) during the
night 31 August–1 September and of HO2+RO2 (within
15–30%) during several nights of the campaign. The model always
overestimated the NO3 measurements made by Differential
Optical Absorption Spectroscopy (DOAS) by up to an order of
magnitude or more, but agreed with the NO3 Cavity Ring-Down
Spectroscopy (CRDS) measurements to within 30–50%. The most
likely explanation of the discrepancy between the two instruments
and the model is the reaction of the nitrate radical with
inhomogeneously distributed NO, which was measured at
concentrations of up to 10 ppt, even though this is not
enough to fully explain the difference between the DOAS measurements
and the model.
A rate of production and destruction analysis showed that radicals
were generated during the night mainly by the reaction of ozone
with light alkenes. The cycling between HO2/RO2
and OH was maintained during the night by the low
concentrations of NO and the overall radical concentration
was limited by slow loss of peroxy radicals to form peroxides. A
strong peak in [NO2] during the night 31 August–1
September allowed an insight into the radical fluxes and the
connections between the HOx and the NO3 cycles.
Citation: Sommariva, R., Pilling, M. J., Bloss, W. J., Heard, D. E., Lee, J. D., Fleming, Z. L., Monks, P. S., Plane, J. M. C., Saiz-Lopez, A., Ball, S. M., Bitter, M., Jones, R. L., Brough, N., Penkett, S. A., Hopkins, J. R., Lewis, A. C., and Read, K. A.: Night-time radical chemistry during the NAMBLEX campaign, Atmos. Chem. Phys., 7, 587-598, doi:10.5194/acp-7-587-2007, 2007.