Illustrating the benefit of using hourly monitoring data on secondary inorganic aerosol and its precursors for model evaluation 1TNO, Business unit Environment, Health and Safety, P.O. Box 80015, 3508 TA Utrecht, The Netherlands
2Energy research Centre of the Netherlands (ECN), P.O. Box 1, 1755 LE Petten, The Netherlands
Received: 26 Mar 2010 – Published in Atmos. Chem. Phys. Discuss.: 10 May 2010 Abstract. Secondary inorganic aerosol, most notably ammonium nitrate and ammonium
sulphate, is an important contributor to ambient particulate mass and
provides a means for long range transport of acidifying components. The
modelling of the formation and fate of these components is challenging.
Especially, the formation of the semi-volatile ammonium nitrate is strongly
dependent on ambient conditions and the precursor concentrations. For the
first time an hourly artefact free data set from the MARGA instrument is
available for the period of a full year (1 August 2007 to 1 August 2008) at
Cabauw, the Netherlands. This data set is used to verify the results of the
LOTOS-EUROS model. The comparison showed that the model underestimates the
SIA levels. Closer inspection revealed that base line values appear well
estimated for ammonium and sulphate and that the underestimation
predominantly takes place at the peak concentrations. For nitrate the
variability towards high concentrations is much better captured, however, a
systematic relative underestimation was found. The model is able to
reproduce many features of the intra-day variability observed for SIA.
Although the model captures the seasonal and average diurnal variation of
the SIA components, the modelled variability for the nitrate precursor gas
nitric acid is much too large. It was found that the thermodynamic
equilibrium module produces a too stable ammonium nitrate in winter and
during night time in summer, whereas during the daytime in summer it is too
unstable. We recommend to improve the model by verification of the
equilibrium module, inclusion of coarse mode nitrate and to address the
processes concerning SIA formation combined with a detailed analysis of the
data set at hand. The benefit of the hourly data with both particulate and
gas phase concentrations is illustrated and a continuation of these
measurements may prove to be very useful in future model evaluation and
improvement studies. Based on our findings we propose to implement a
monitoring strategy using three levels of detail within the Netherlands.
Revised: 13 Sep 2011 – Accepted: 13 Sep 2011 – Published: 08 Nov 2011
Citation: Schaap, M., Otjes, R. P., and Weijers, E. P.: Illustrating the benefit of using hourly monitoring data on secondary inorganic aerosol and its precursors for model evaluation, Atmos. Chem. Phys., 11, 11041-11053, doi:10.5194/acp-11-11041-2011, 2011.