Diurnal variations in major rainwater components at a coastal site in North Carolina

Concentrations of several major rainwater components were determined in rai n events occurring during the early morning hours (12:00 midnight to 6:00 a .m.) and during the afternoon (12:00 noon to 6:00 p.m.) to examine possible diurnal variations. Generally, rainwater components with gas phase origins (H+, NO3-, formaldehyde, H2O2, formic acid, acetic acid, pyruvic acid, oxa lic acid, and lactic acid) had higher concentrations during p.m. rain event s compared to a.m. events. Although source strengths of both biogenic and a nthropogenic rainwater components are generally higher during the daytime, nocturnal removal of a wide variety of components in similar proportions (a pproximately 2-3 x less at night) indicates a physical rather than a chemic al process affecting diurnal variations. Rainwater components with aerosol origins (Cl- and SO42-) displayed the opposite diurnal pattern or showed no diurnal variation. Possible reasons for these variations include one or bo th of the following scenarios: (1) the formation of dew at night removes ga s phase atmospheric gasses but not aerosols or (2) during the night, a mari ne air mass containing lower concentrations of all analytes and higher conc entrations of Cl- is advected into the area. (C) 2001 Elsevier Science Ltd. All rights reserved.