Vertical Profiles and Seasonal Variations of Key Parameters Controlling Particle Formation and Growth at Storm Peak Laboratory

ABSTRACT

Here we compare model simulated number concentrations of condensation nuclei larger than 10 nm (CN10) in 2009 with those measured at the Storm Peak Laboratory (SPL), a high elevation mountain-top observatory in northwestern Colorado, US. We also investigate vertical profiles and seasonal variations of key parameters controlling particle formation and growth over this remote mountain-top site. The model overall captures absolute values of CN10 and their variations, especially in the spring months where regional scale new particle formation (NPF) occurred frequently. The model is able to predict the right magnitude of background CN10 values in July and August but it fails to reproduce the short-term spikes in CN10 and thus under-predicts the mean CN10 in these two months. The vertical profiles of key parameters relevant to NPF, including temperature and concentrations of SO₂, secondary organic gases (SOG), OH, H₂SO₄ and low volatility SOG, show clear seasonal variations that lead to relatively high frequency of NPF in the spring and fall. Vertically, high concentrations of precursors and aerosol number concentrations are generally confined to the boundary layer and lower troposphere.