Aerosol physics, chemistry and cloud condensation nuclei at the ocean surface, VOCALS-REx 2008

Aerosol measurements were made at the ocean surface in the Eastern South Pacific during VOCALS-REx along 20 degrees South from the Chilean coast to 85 degrees West in October and November of 2008 on the NOAA RV Ronald H. Brown. The measurements included total number concentration and number-size distribution from 3 nm to 10 µm diameter, cloud condensation nucleus concentration at 0.1 to 0.6 % supersaturation, and particle chemistry from 80 to 800nm diameter.

Aerosol concentrations ranged from low (<100 particles per cubic centimeter) in regions remote from the coast with active cloud fields to moderate remote marine levels (ca. 500 per cc) nearer the coast and in MBL air masses advected from the coast. These particles were largely limited to the size range greater than 30 nm and were distributed in two typical modes: an Aitken number mode centered around 50 nm and an accumulation mode centered around 170 nm. The accumulation mode generally dominated the number fraction. A few isolated events of higher concentration at sizes smaller than the Aitken mode related to recent new particle formation or entrainment were observed.

The submicrometric aerosol mass was dominated by sulfate ions at concentrations of 0.9 ± 0.7 micrograms per cubic meter and organic compounds at 0.6 ± 0.4 micrograms per cubic meter with no measurable nitrate and low ammonium. Saturated aliphatic groups were observed in all samples and composed 41 ± 27% of the OM while carboxylic acid groups composed 32 ± 23% of OM.

CCN concentration at 0.1, 0.3 and 0.6% supersaturation averaged 140, 215 and 270 per cc, respectively over the VOCALS-Rex cruise. In areas of active cloud formation and precipitation the values were 25, 50 and 100 per cc.