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 μM. Nitrite
concentrations did not correlate with precipitation volume,
suggesting a continuous supply of nitrite during rain
events possibly by slow scavenging of gas-phase material
such as HONO(g) or NO2(g) or in-cloud oxidation of
other reduced forms of nitrogen. Nitrite levels exhibited
no seasonal oscillations, which is in contrast to other rainwater
parameters at this site such as pH, nitrate, non-seasalt
sulfate (NSS) and ammonium. Concentrations of nitrite did
not correlate with concentrations of pollutant indicators
(pH, nitrate, and NSS). The concentration of nitrite in both
winter El Nino rains and summer tropical rains was less
than half its concentration in non-El Nino or non-tropical
events, suggesting a possible terrestrial source of nitrite or
nitrite precursor. Controlled laboratory studies demonstrated
that hydrogen peroxide can oxidize nitrite in rainwater
at environmentally relevant H+, H2O2, and NO2
- concentra
tions. Nitrite oxidation by H2O2 in the aqueous phase has
important ramifications with respect to N cycling and acid
generation within the troposphere.
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