Particle Size Distribution O F Nitrate and Sulfate in the Marine Atmosphere

Cascade impactor samples were collected a t coastal sites on Sal Island, Barbados, and Virginia Key, Miami during 1974 and a t two Miami coastal sites on Virginia Key and Key Biscayne during 1981. In all of the samples, the majority of t h e ni t rate mass was found on intermediate size particles and exhibited a mass median diameter (MMD) of about 4 pm. The ratio of t h e MMD of ni t rate t o t h a t of sea-salt (about 7 pm) varied from 0.54 t o 0.60 which indicates tha t the ni t rate mass distribution is well defined by t h e surface a rea distribution of t h e sea-salt aerosols. This sharply contrasts with the distribution of non-sea-salt sulfate (also produced from gas-to-particle conversion reactions) which is present primarily on submicron aerosols. The lower levels of ni t rate in t h e small particles a r e probably a consequence of t h e higher volatility and photochemical reactivity of the ni t rate compounds expected t o exist in the acidic aerosols.