Isotopic evidence that alkyl nitrates are important to aerosol nitrate
formation in the Equatorial Pacific
Abstract
Concentrations and the stable isotopic composition of bulk aerosol
nitrate (NO3-) were quantified from
two fall GEOTRACES cruises: 1) Alaska–Tahiti (GP15; n=22) and 2)
Peru–Tahiti (GP16; n=17) to explore the hypothesis that marine
emissions influence aerosol NO3- in
the Equatorial Pacific. The
δ15N-NO3- ranged
from -14.5–0.5‰, with lowest values far from the coast and primarily
reflecting a shift in sources. The δ18O- and
Δ17O-NO3- were both
high (65.2–85.4‰ and 21.4–30.7‰, respectively) and decreased away from
continental regions, reflecting a shift in the oxidants that influence
the formation of NO3-. Transport
modeling and co-occurrence of low δ15N,
δ18O and Δ17O provided evidence for
an important influence of alkyl nitrates (RONO2)
on aerosol NO3-
formation. Based on the Δ17O, we quantified that the
contribution of RONO2 to aerosol
NO3- can be as high as 48% (range
15–48%). We were also able to estimate an average
δ15N-RONO2 of -22.9 ± 19.1‰.