Hygroscopicity of marine aerosol: Closure, long term observation and cloud condensation potential

Abstract

Marine aerosols have a profound impact on the global climate system by scattering solar radiation and serving as seeds for cloud formation. However, the marine aerosols in current models are still poorly represented and lack constraints. In this work, the physico-chemical properties of marine aerosol were obtained in Mace Head Atmospheric Research Station on the west coast of Galway, Ireland. The worked is centred by the data obtained by humidity tandem differential mobility analyzer (HTDMA) and combined with other aerosol measurements, e.g. aerosol mass spectrometer, scanning mobility particle sizer (SMPS). This work aims to characterise marine aerosols in terms of hygroscopicity and their relevant climate impacts and consists of the following sections: • We demonstrate that the hygroscopicity of marine aerosols can be predicted in high temporal resolution by using bulk PM1 chemical composition. This is the first time that the hygroscopicity of marine aerosol has been predicted by the chemical composition that contains sea salt. • We present a statistical analysis of a five-year dataset of hygroscopicity measurement, which is the longest dataset of its kind to date. From this, a contrasting seasonal difference between marine and continental aerosols has been found. • The number concentrations of cloud condensation nuclei (CCN) are predicted by using hygroscopicity and chemical composition. The impact of common assumptions, including size-dependent hygroscopicity and mixing state are quantified. • The sea spray aerosol is one of the most important species of marine aerosol, and the sea spray number is crucial in determining the CCN numbers. However, the sea spray number cannot be measured by conventional methods. As such, we have developed a method to use size-resolved hygroscopicity data to distinguish the sea spray and other species, and we found that the conventional method underestimated the sea spray number by up to tenfold, thus greatly overlooking their climate effects.