Composition of 15–85 nm particles in marine air

M J Lawler,C O'Dowd,J Whitehead,G Mcfiggans,J N Smith,C Monahan

doi:10.5194/acp-14-11557-2014

Abstract

Abstract. The chemical composition of 15–85 nm diameter particles was measured at Mace Head, Ireland, during May 2011 using the TDCIMS (thermal desorption chemical ionization mass spectrometer). Measurable levels of chloride, sodium, and sulfate were present in essentially all collected samples of these particles at this coastal Atlantic site. Acetaldehyde and benzoic acid were also frequently detected. Concomitant particle hygroscopicity observations usually showed a sea-salt mode and a lower hygroscopicity mode with growth factors near to that of ammonium sulfate. There were many periods lasting from hours to about 2 days during which the 10–60 nm particle number increased dramatically in polar oceanic air. These periods were correlated with the presence of benzoic acid in the particles and an increase in the number of lower hygroscopicity mode particles. Very small (< 10 nm) particles were also present, suggesting that new particle formation contributed to these nanoparticle enhancement events.

Highlights

Particles in the atmosphere play important roles in the global climate through direct interaction with radiation and by acting as cloud condensation nuclei (CCN)
We present measurements of nanoparticle chemical composition and hygroscopicity made in marine air at Mace Head during May 2011
A new particle formation event was observed at sea about 8 h upwind of Mace Head, and the resulting plume showed nanoparticle number enhancements when it reached Mace Head (Ehn et al, 2010)

Summary

Introduction

Particles in the atmosphere play important roles in the global climate through direct interaction with radiation and by acting as cloud condensation nuclei (CCN). In the marine boundary layer (MBL), where cloud water vapor supersaturations are typically around 0.2 %, even very hygroscopic sea-salt aerosols must be greater than 70 nm in diameter before they are activated into cloud droplets (Hoppel et al, 1996; Seinfeld and Pandis, 1997). For this reason, in order for homogeneously nucleated particles to have a significant impact on cloud formation, they must grow swiftly enough to CCN size before they are lost by coagulation onto existing aerosol. Net condensation of low volatility vapors and/or multiphase reactive uptake are required to accomplish this growth (Khvorostyanov and Curry, 2007; Donahue et al, 2011)

Results

Discussion

Conclusion