Chemical Composition and Cloud Nucleation Ability of Marine Aerosol

Abstract

This study is focused on the chemical composition and cloud nucleation ability of marine aerosol based on two cruise researches over Pacific Ocean and North Atlantic Ocean respectively. Implications of CLAW hypothesis and the factors influencing its validity are analyzed for the contemporary era with ever-increasing pollution.

The pacific cruise started from Punta Arenas, Chile and ended in Seattle, WA during March-April of 2010. Raman microspectroscopy (RMS) was employed to identify the chemical composition and mixing conditions of single particles collected. By analyzing multiple particles in a collected ensemble, the degree of external/internal mixing of particles was also determined. Atmospheric aerosol concentration, cloud condensation nuclei (CCN) concentration, and chlorophyll a concentration in the underlying water (a metric for phytoplankton biomass in the ocean), were also measured. Our results indicate that long chain organic molecules were prevalent in the marine aerosol samples throughout the cruise. Long chain organic compounds tended to stay mixed with other organic and inorganic components. The influence of marine organic aerosols on cloud nucleation ability is analyzed.

The North Atlantic cruise started from Woods Hole, MA and returned back to the same location during June-July 2011. The cruise passed through a wide range of conditions, including areas of high phytoplankton biomasses and extremely high DMS levels (over 1800 pptv). Aerosol concentration, cloud condensation nuclei (CCN) concentration, particle size distribution, as well as surface seawater and atmospheric DMS concentrations were performed simultaneously during the cruise. HYSPLIT back trajectories were used to classify air mass origins. Even though continental sources increased the total aerosol population, it depressed the effective CCN concentrations possibly due to the competition in particle growth. Continuous high CCN and elevated DMS concentrations over the open ocean occur concurrently, which can be explained by enhanced nucleation and condensational growth of aerosols in marine boundary layer (MBL) resulting from the DMS oxidation or primary aerosols from the sea surface. Our data also indicated that uncertainties remain in sea spray aerosol production flux function, especially for particles with dry diameter smaller than 200 nm.