National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2008

Isotopic analysis of aerosol sulfate and nitrate during ITCT-2k2: Determination of different formation pathways as a function of particle size

Patris, N., S.S. Cliff, P.K. Quinn, M. Kasem, and M.H. Thiemens

J. Geophys. Res., 112, D23301, doi: 10.1029/2005JD006214 (2007)

The triple isotopic composition of oxygen in sulfate and nitrate, and the sulfur isotopic composition of the sulfate fine fraction, have been measured on size-segregated aerosol samples collected at Trinidad Head, coastal California, alongside the ITCT-2k2 campaign in April–May 2002. The isotopic anomaly O = O – 0.52 × O has been determined in both sulfate and nitrate and was used as a specific tracer of the formation pathways of these species. Coarse mode sulfate in all samples exhibited a small but significant O anomaly indicating either uptake or in situ formation of secondary sulfate on sea spray. Non-sea-salt sulfate O in the coarse fraction is consistent with (1) either primarily coagulation of finer sulfate particles, when O is low in all size fractions, or (2) ozone-driven oxidation of SO within the sea spray, as observed in the relatively higher O in coarse particles compared to fine. It is proposed that tripleisotope measurements of sulfate oxygen can be used to quantify the budget of in situ sea spray nss-SO4 formation. The O measured in size-resolved nitrate revealed, for the first time, differences in the nitrate formation budget as a function of particle size in a given air mass. The coarse particle nitrate possessed a higher O, suggesting a relatively larger NO hydrolysis contribution to the nitrate formation budget compared to fine particles where homogeneous formation is more important. We conclude that the complete isotope ratio analysis may provide a basis for future modeling of the formation and transformation processes of the soluble aerosol, based on direct observation of the mechanisms.

Feature Publications | Outstanding Scientific Publications

Contact Sandra Bigley |