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

Abstract

[1] 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 anomalyO 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 D 17O anomaly indicating either uptake or in situ formation of secondary sulfate on sea spray. Non-sea-salt sulfate D 17O in the coarse fraction is consistent with (1) either primarily coagulation of finer sulfate particles, when D 17O is low in all size fractions, or (2) ozone-driven oxidation of SO 2 within the sea spray, as observed in the relatively higher D 17O 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-SO 4 formation. The D 17O 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 D 17 O, suggesting a relatively larger N 2 O 5 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.

Tales of volcanoes and El-Niño southern oscillations with the oxygen isotope anomaly of sulfate aerosol

“…1A and 3. The volcanic sulfate aerosol showed less enrichment in (13,18) indicate the predominant role of stratospheric OH and HO 2 radicals (30,39). The concentration of these radicals in the stratosphere depends on ozone, water vapor, CH 4 , and NO x concentrations (40), and it is suggested to be 1.5 ± 0.3 × 10 6 molecules per cubic centimeter in the tropics using the global chemistry transport model (41).…”

“…The oxidation of aqueous SO 2 by O 3 and H 2 O 2 far exceeds gas phase rates and is pH-dependent (11,12). The oxygen-triple isotopic composition of sulfate aerosols has been demonstrated to be a useful diagnostic tool to distinguish and quantify reaction pathways and to determine the paleooxidant levels on centennial to millennium (glacial period) time scales to present-day environments (13)(14)(15)(16)(17)(18) (19,20). The ozone molecule is a unique quantitative tracer of oxidation reactions because it possesses the highest enrichment in the heavier isotopes of oxygen (70-120‰) and oxygen isotope anomaly (Δ 17 O = 25-30‰).…”

Implications of regional surface ozone increases on visibility degradation in southeast China

“…Note that SO 2 emission in east China also kept increasing from 1985 to (Streets et al, 2000Lu et al, 2010), suggesting that the visibility degradation in southeast China may in part be due to transport of secondary sulphate formed upwind (i.e., over the east China coast). Measurements of the mass-independent fractionated oxygen isotopes in sulphate allow the primary and secondary sulphate contributions to be identified, and the oxidation pathways of secondary sulphate to be quantified Alexander et al, 2005;Patris et al, 2007;Dominguez et al, 2008). Such measurements can bring us closer to identifying the dominant oxidation mechanisms in the future.…”

The impact of anthropogenic emissions on atmospheric sulfate production pathways, oxidants, and ice core Δ<sup>17</sup>O(SO<sub>4</sub><sup>2–</sup>)

“…Oxygen triple-isotope ( 16 O, 17 O, 18 O) measurements of sulfate have been used previously to infer the atmospheric formation pathways of sulfate in the present Alexander et al, 2005Alexander et al, , 2009Patris et al, 2007;Dominguez et al, 2008) and paleo- (Alexander et al, 2002(Alexander et al, , 2003(Alexander et al, , 2004Kunasek et al, 2010) atmosphere. Most chemical and physical processes fractionate isotopes in a mass-dependent manner.…”