Nitrite variability in coastal North Carolina rainwater and its impact on the nitrogen cycle in rain

The concentration range for nitrite (NO2-) in 115 rain samples collected in Wilmington, NC, from June 1996 through February 1998 was 0.022-0.603 mu M. Nitrite concentrations did not correlate with precipitation volume, sugges ting a continuous supply of nitrite during rain events possibly by slow sca venging of gas-phase material such as HONO(g) or NO2(g) or in-cloud oxidati on of other reduced forms of nitrogen. Nitrite levels exhibited no seasonal oscillations,which is in contrast to other rainwater parameters at this si te such as pH,, nitrate, non-seasalt sulfate (NSS) and ammonium. Concentrat ions of nitrife did not correlate with concentrations of pollutant indicato rs (pH, nitrate, and NSS). The concentration of nitrite in both winter El N ine rains and summer tropical rains was less than half its concentration in non-Fl Nine or nan-tropical events, suggesting a possible terrestrial sour ce of nitrite or nitrite precursor. Controlled laboratory studies demonstra ted that hydrogen peroxide can oxidize nitrite in rainwater at environmenta lly relevant H+, H2O2, and NO2- concentrations. Nitrite oxidation by H2O2 i n the aqueous phase has important ramifications with respect to N cycling a nd acid generation within the troposphere.