New Instrument for Measuring Size-resolved Submicron Sea Spray Particle Production From Ocean

Abstract:

Marine aerosols play an important role in controlling the Earth’s radiation balance, cloud formation and microphysical properties, and the chemistry of the marine atmosphere. As aerosol effects on climate are estimated from the difference between model simulations with present-day and with preindustrial aerosol and precursor emissions, accurate knowledge of size‐ and composition‐dependent production flux of sea spray particles is important for correct assessment of the role of anthropogenic aerosols in climate change. One particular knowledge gap in sea spray particle emissions resides in yet uncharacterized contributions of sea spray to the cloud condensation nuclei (CCN) budget over the marine boundary layer. The chemical composition of 50 to 200 nm sized sea spray particles, most critical to modeling CCN concentration from size distribution data is often simplified as purely organic, purely sea-salt or mixture of both. The lack of accurate information of the size‐dependent production flux of sub-micron sea spray particles prevents the modeling community from resolving discrepancies between model-predicted and measured CCN number concentration in the marine boundary layer.

We designed a new system for size-selected sea spray aerosol flux measurement that is composed of a 3D sonic anemometer, two thermodenuders, three differential mobility analyzers, two condensation particle counters, and a CCN counter. The system is designed to operate in both Eddy Covariance (EC) and Relaxed Eddy Accumulation (REA) modes. The system is based on the volatility/humidified tandem differential mobility analyzer technique and is therefore designed to measure the size-resolved turbulent fluxes of sub-micron sized sea-salt particles for a wide range of meteorological, hydrological and ocean chemical/biological conditions. The method and the setup will be presented along with some results from a recent field-deployment of the instrument at the North Carolina coast. This presentation will also show some laboratory results for the anemometer wind corrections using a custom built “ship-simulator” and a motion correction package.