Sulfate formation in sea‐salt aerosols: Constraints from oxygen isotopes

Alexander, Becky

doi:10.1029/2004jd005659

Cited by 367 publications

(412 citation statements)

References 93 publications

(131 reference statements)

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“…Most Hg oxidation by mass occurs in the extratropical free troposphere, consistent with the Br distribution (Schmidt et al, 2016), and is faster in the Northern Hemisphere because of higher NO 2 concentrations. Hg 0 oxidation in was fastest in the Southern Ocean MBL due to high Br concentrations from sea salt aerosol debromination, but debromination in that region is unlikely since the sea salt aerosol remains alkaline (Murphy et al, 1998;Alexander et al, 2005;Schmidt et al, 2016). In general, the addition of second-stage oxidants HO 2 and NO 2 shifts Hg oxidation to lower latitudes relative to Holmes et al (2010).…”

Section: Atmosphere-ocean Couplingmentioning

confidence: 99%

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

et al. 2017

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Abstract. Mercury (Hg) is emitted to the atmosphere mainly as volatile elemental Hg 0 . Oxidation to water-soluble Hg II plays a major role in Hg deposition to ecosystems. Here, we implement a new mechanism for atmospheric Hg 0 / Hg II redox chemistry in the GEOS-Chem global model and examine the implications for the global atmospheric Hg budget and deposition patterns. Our simulation includes a new coupling of GEOS-Chem to an ocean general circulation model (MITgcm), enabling a global 3-D representation of atmosphereocean Hg 0 / Hg II cycling. We find that atomic bromine (Br) of marine organobromine origin is the main atmospheric Hg 0 oxidant and that second-stage HgBr oxidation is mainly by the NO 2 and HO 2 radicals. The resulting chemical lifetime of tropospheric Hg 0 against oxidation is 2.7 months, shorter than in previous models. Fast Hg II atmospheric reduction must occur in order to match the ∼ 6-month lifetime of Hg against deposition implied by the observed atmospheric variability of total gaseous mercury (TGM ≡ Hg 0 + Hg II (g)). We implement this reduction in GEOS-Chem as photolysis of aqueous-phase Hg II -organic complexes in aerosols and clouds, resulting in a TGM lifetime of 5.2 months against deposition and matching both mean observed TGM and its variability. Model sensitivity analysis shows that the interhemispheric gradient of TGM, previously used to infer a longer Hg lifetime against deposition, is misleading because Southern Hemisphere Hg mainly originates from oceanic emissions rather than transport from the Northern Hemisphere.The model reproduces the observed seasonal TGM variation at northern midlatitudes (maximum in February, minimum in September) driven by chemistry and oceanic evasion, but it does not reproduce the lack of seasonality observed at southern hemispheric marine sites. Aircraft observations in the lowermost stratosphere show a strong TGM-ozone relationship indicative of fast Hg 0 oxidation, but we show that this relationship provides only a weak test of Hg chemistry because it is also influenced by mixing. The model reproduces observed Hg wet deposition fluxes over North America, Europe, and China with little bias (0-30 %). It reproduces qualitatively the observed maximum in US deposition around the Gulf of Mexico, reflecting a combination of deep convection and availability of NO 2 and HO 2 radicals for second-stage HgBr oxidation. However, the magnitude of this maximum is underestimated. The relatively low observed Hg wet deposition over rural China is attributed to fast Hg II reduction in the presence of high organic aerosol concentrations. We find that 80 % of Hg II deposition is to the global oceans, reflecting the marine origin of Br and low concentrations of organic aerosols for Hg II reduction. Most of that deposition takes place to the tropical oceans due to the availability of HO 2 and NO 2 for second-stage HgBr oxidation.

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Section: Atmosphere-ocean Couplingmentioning

confidence: 99%

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

et al. 2017

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“…The SO 2 molecules adsorbed in the sea salt particles are oxidized mainly by O 3 like in the in-cloud S(IV) oxidation. Following Alexander et al [2005] and Chameides and Stelson [1992], we assume that the alkalinity of sea salt particles is rapidly titrated by SO2. Thus we only consider sulfate formation on fresh sea salt particles by oxidation with O 3 at a constant pH = 8 (fresh sea salt particles were diagnosed as the particles being only composed of sea salt and water).…”

Section: Heterogeneous Chemistrymentioning

confidence: 99%

“…Thus we only consider sulfate formation on fresh sea salt particles by oxidation with O 3 at a constant pH = 8 (fresh sea salt particles were diagnosed as the particles being only composed of sea salt and water). We do not take into account the sea salt alkalinity titration by HNO 3 (which can be important in tropical regions where NOx emissions dominate over SO 2 emissions [Alexander et al, 2005]), and the competing aerobic S(IV) oxidation proposed by Hoppel and Caffrey [2005].…”

Section: Heterogeneous Chemistrymentioning

confidence: 99%

Trace gas and aerosol interactions in the fully coupled model of aerosol‐chemistry‐climate ECHAM5‐HAMMOZ: 1. Model description and insights from the spring 2001 TRACE‐P experiment

et al. 2008

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[1] In this paper, we introduce the ECHAM5-HAMMOZ aerosol-chemistry-climate model that includes fully interactive simulations of Ox-NOx-hydrocarbons chemistry and of aerosol microphysics (including prognostic size distribution and mixing state of aerosols) implemented in the General Circulation Model ECHAM5. The photolysis rates used in the gas chemistry account for aerosol and cloud distributions and a comprehensive set of heterogeneous reactions is implemented. The model is evaluated with trace gas and aerosol observations provided by the TRACE-P aircraft experiment. Sulfate concentrations are well captured but black carbon concentrations are underestimated. The number concentrations, surface areas, and optical properties are reproduced fairly well near the surface but underestimated in the upper troposphere. CO concentrations are well reproduced in general while O 3 concentrations are overestimated by 10-20 ppbv. We find that heterogeneous chemistry significantly influences the regional and global distributions of a number of key trace gases. Heterogeneous reactions reduce the ozone surface concentrations by 18-23% over the TRACE-P region and the global annual mean O 3 burden by 7%. The annual global mean OH concentration decreases by 10% inducing a 7% increase in the global CO burden. Annual global mean HNO 3 surface concentration decreases by 15% because of heterogenous reaction on mineral dust. A comparison of our results to those from previous studies suggests that the choice of uptake coefficients for a given species is the critical parameter that determines the global impact of heterogeneous chemistry on a trace gas (rather than the description of aerosol properties and distributions). A prognostic description of the size distribution and mixing state of the aerosols is important, however, to account for the effect of heterogeneous chemistry on aerosols as further discussed in the second part of this two-part series.Citation: Pozzoli, L., I. Bey, S. Rast, M. G. Schultz, P. Stier, and J. Feichter (2008), Trace gas and aerosol interactions in the fully coupled model of aerosol-chemistry-climate ECHAM5-HAMMOZ: 1. Model description and insights from the spring 2001 TRACE-P experiment,

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“…There have also been numerous studies that have experimentally quantified the pressure and temperature dependence of the isotopic enrichments (10,11). Most recently, the transfer of the ⌬ 17 O anomaly from ozone to other compounds during oxidation reactions (via atom transfer, e.g., mass balance) has been used to elucidate chemical oxidation pathways in modern atmospheres (16)(17)(18)(19)(20)(21). These include ⌬ 17 O observations in atmospheric nitrate, sulfate, CO 2 , and N 2 O.…”

mentioning

confidence: 99%

The role of symmetry in the mass independent isotope effect in ozone

Michalski

Bhattacharya

2009

Proc. Natl. Acad. Sci. U.S.A.

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Understanding the internal distribution of ''anomalous'' isotope enrichments has important implications for validating theoretical postulates on the origin of these enrichments in molecules such as ozone and for understanding the transfer of these enrichments to other compounds in the atmosphere via mass transfer. Here, we present an approach, using the reaction NO 2 ؊ ؉ O3, for assessing the internal distribution of the (7) and non-mass-dependent (NOMAD) (8, 9).The most thoroughly studied MIF system is that of ozone formation. Ozone generated by electric discharge or UV photolysis can produce ⌬ 17 O values of 30-40‰ (‰ ϭ parts per thousand). There have also been numerous studies that have experimentally quantified the pressure and temperature dependence of the isotopic enrichments (10, 11). Most recently, the transfer of the ⌬ 17 O anomaly from ozone to other compounds during oxidation reactions (via atom transfer, e.g., mass balance) has been used to elucidate chemical oxidation pathways in modern atmospheres (16-21). These include ⌬ 17 O observations in atmospheric nitrate, sulfate, CO 2 , and N 2 O. ⌬ 17 O variations in atmospheric nitrate and sulfate are intriguing because they have opened the possibility of using these ⌬ 17 O variations in ice cores as a proxy for paleo-oxidation chemistry (22,23). Modeling such transfer reactions, however, requires knowledge of the internal distribution of the ⌬ 17 O anomaly, i.e., how much is contained in the central versus terminal atoms of ozone, because many atmospheric oxidations are thought to occur through terminal-only transition states.Theories as to the origin of the MIF effect have taken many turns (7,8,24,25), and some theories seem more adept at handling specific experimental cases than others. Most have symmetry as the main, albeit ad hoc, causal mechanism for producing MIF. Recent work by Marcus and coworkers (26-28) is perhaps the most thorough treatment, and they have suggested that nonstatistical RRKM effects arise because of differences in the rovibronic coupling efficiency of the asymmetric molecule when compared with the symmetric isomer. Recent NO 2 spectroscopic data appear to bear the theory out (29), but the uncertainties in that study remain significant, and no mass spectrometer isotope data on the unimolecular decay of NO 2 are available. Because the basis of the ozone MIF theory is symmetry driven, it is implied that the anomalous enrichment must be contained in the terminal atoms of ozone. To be clear, there maybe overall isotopic enrichment (␦ 18 O, ␦ 17 O) distributed throughout the molecule based on isotopologue zero-point energy differences (30), but the 17 O excess (⌬ 17 O) is expected to be only in the terminal position. Others, however, have argued against the symmetry theory (31-33) and have placed anomalous enrichments, even negative ⌬ 17 O values (34), throughout ozone in an attempt to reconcile experimental observations. Precise and accurate measurements of ozone's ⌬ 17 O internal distribution is therefore needed to test the symmet...

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Sulfate formation in sea‐salt aerosols: Constraints from oxygen isotopes

Cited by 367 publications

References 93 publications

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

Trace gas and aerosol interactions in the fully coupled model of aerosol‐chemistry‐climate ECHAM5‐HAMMOZ: 1. Model description and insights from the spring 2001 TRACE‐P experiment

The role of symmetry in the mass independent isotope effect in ozone

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