Combined effects of surface conditions, boundary layer dynamics and chemistry on diurnal SOA evolution

R H H Janssen,J Vilà-Guerau De Arellano,P Kabat,D K Farmer,C C Van Heerwaarden,I Mammarella,L N Ganzeveld,J L Jimenez

doi:10.5194/acp-12-6827-2012

Abstract

Abstract. We study the combined effects of land surface conditions, atmospheric boundary layer dynamics and chemistry on the diurnal evolution of biogenic secondary organic aerosol in the atmospheric boundary layer, using a model that contains the essentials of all these components. First, we evaluate the model for a case study in Hyytiälä, Finland, and find that it is able to satisfactorily reproduce the observed dynamics and gas-phase chemistry. We show that the exchange of organic aerosol between the free troposphere and the boundary layer (entrainment) must be taken into account in order to explain the observed diurnal cycle in organic aerosol (OA) concentration. An examination of the budgets of organic aerosol and terpene concentrations show that the former is dominated by entrainment, while the latter is mainly driven by emission and chemical transformation. We systematically investigate the role of the land surface, which governs both the surface energy balance partitioning and terpene emissions, and the large-scale atmospheric process of vertical subsidence. Entrainment is especially important for the dilution of organic aerosol concentrations under conditions of dry soils and low terpene emissions. Subsidence suppresses boundary layer growth while enhancing entrainment. Therefore, it influences the relationship between organic aerosol and terpene concentrations. Our findings indicate that the diurnal evolution of secondary organic aerosols (SOA) in the boundary layer is the result of coupled effects of the land surface, dynamics of the atmospheric boundary layer, chemistry, and free troposphere conditions. This has potentially some consequences for the design of both field campaigns and large-scale modeling studies.

Highlights

A large part of submicron atmospheric particulate material is organic (Hallquist et al, 2009; Jimenez et al, 2009)
When emitted at the land surface, they enter into the atmospheric boundary layer (BL), the lowest part of the atmosphere, which is characterized by strong turbulent motions that are largely influenced by the underlying land surface and the free troposphere (FT) on top of it
We have studied the integrated effects of land surface, chemistry, and entrainment on the diurnal evolution of Secondary organic aerosols (SOA), using MXLCH-SOA, a model that reproduces the dynamics of a diurnal convective atmospheric boundary layer and the chemical transformations of terpenes and their oxidants that lead to SOA formation (Fig. 1)

Summary

Introduction

A large part of submicron atmospheric particulate material is organic (Hallquist et al, 2009; Jimenez et al, 2009). Secondary organic aerosols (SOA) which are formed in the atmosphere from oxidation of high-volatility precursors are an important contributor to the total organic aerosol budget. The importance of SOA in new particle formation (Metzger et al, 2010; Laaksonen et al, 2008; O’Dowd et al, 2002) and the growth of atmospheric particles to cloud condensation nuclei (Riipinen et al, 2011; Slowik et al, 2010; Tunved et al, 2006) is well established. Formation of SOA from gas-phase species depends on the emissions of these species and their processing in the atmosphere.

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