An analysis of rapid increases in condensation nuclei concentrations at a remote coastal site in western Ireland

Massive "bursts" in condensation nuclei (CN) concentration were recorded at a remote site on the west Irish coast during campaigns in summer 1996 and spring/summer 1997. Number concentrations of 3-7 nm diameter CN were observ ed to rise daily from 10(2)-10(3) UP to similar to 10(5) /cm(3) for 1-3 hou rs. Data were collected as part of the Atmospheric Chemistry Studies in the Oceanic Environment program. In a previous paper the burst phenomenon was linked to the movement of the tide, and it was suggested that enhanced biog enic emissions occurred near low tide with concomitant rapid homogeneous ga s phase CN formation. In this paper possible chemical mechanisms for the bu rst phenomenon are investigated. Two approaches are adopted. First, by assu ming a 20:80 sulfate:water molar composition and calculating the number dis tribution using data from condensation particle counters, the total mass of CN formed during a burst is evaluated. This is compared with that mass of sulfate produced by OH-initiated dimethyl sulfide (DMS) oxidation, The proc edure is termed "mass balance." Second, a variety of chemical species are c oplotted with tidal height. DMS oxidation is not believed to play a major r ole in CN formation at this site because (1) the mass balance calculations imply ambient DMS concentrations higher than those observed, and (2) gas ph ase HCl, HNO3, SO2, and NH3 did not exhibit any discernible correlation wit h tidal height. Further, none of the suite of observed nonmethane hydrocarb ons or DMS showed a tidal relation. No mechanism has to date been convincin gly identified for the burst phenomenon.