Atmospheric Sulfur Species Research Articles

Approaches for Retrieving Sulfur Species Abundances from Dual X–Ka-band Radio Occultations of Venus with EnVision and VERITAS

The EnVision and VERITAS missions to Venus will fly with X- and Ka-band telecommunications channels, which can be used to conduct radio occultation studies of Venus’ atmosphere. While link attenuation measurements during prior S- and X-band occultation experiments have been used to determine vertical profiles of H2SO4 vapor abundance, the addition of the Ka-band channel introduces greater sensitivity to the abundances of H2SO4 aerosols and SO2 gas, permitting the retrieval of their vertical profiles from dual-band measurements. Such measurements would be valuable in the assessment of chemical and dynamical processes governing short- and long-term variability in Venus’ atmosphere. This paper considers the sensitivity of the X–Ka-band radio attenuation measurement to these atmospheric constituents, as well as uncertainties and regularization approaches for conducting retrievals of these atmospheric sulfur species from future occultation experiments. We introduce methods for seeding maximum likelihood estimation retrievals using shape models and simple atmospheric transport constraints. From simulated retrievals, we obtain mean errors of the order of 0.5 ppm, 20 ppm, and 10 mg m−3 for H2SO4 vapor, SO2, and H2SO4 aerosol abundances, respectively, for simultaneous retrieval.

Large-volume air sample system for measuring <sup>34</sup>S∕<sup>32</sup>S isotope ratio of carbonyl sulfide

Abstract. Knowledge related to sulfur isotope ratios of carbonyl sulfide (OCS or COS), the most abundant atmospheric sulfur species, remains scarce. An earlier method developed for sulfur isotopic analysis for OCS using S+ fragmentation by an isotope ratio mass spectrometer is inapplicable for ambient air samples because of the large samples required (approx. 500 L of 500 pmol mol−1 OCS). To overcome this difficulty, herein we present a new sampling system for collecting approximately 10 nmol of OCS from ambient air coupled with a purification system. Salient system features are (i) accommodation of samples up to 500 L (approx. 10 nmol) of air at 5 L min−1; (ii) portability of adsorption tubes (1∕4 in. (0.64 cm) outer diameter, 17.5 cm length, approximately 1.4 cm3 volume) for preserving the OCS amount and δ34S(OCS) values at −80 ∘C for up to 90 days and 14 days; and (iii) purification OCS from other compounds such as CO2. We tested the OCS collection efficiency of the systems and sulfur isotopic fractionation during sampling. Results show precision (1σ) of δ34S(OCS) values as 0.4 ‰ for overall procedures during measurements for atmospheric samples. Additionally, this report presents diurnal variation of δ34S(OCS) values collected from ambient air at the Suzukakedai campus of the Tokyo Institute of Technology located in Yokohama, Japan. The observed OCS concentrations and δ34S(OCS) values were, respectively, 447–520 pmol mol−1 and from 10.4 ‰ to 10.7 ‰ with a lack of diurnal variation. The observed δ34S(OCS) values in ambient air differed greatly from previously reported values of δ34S(OCS) = (4.9±0.3) ‰ for compressed air collected at Kawasaki, Japan, presumably because of degradation of OCS in cylinders and collection processes for that sample. The difference of atmospheric δ34S(OCS) values between 10.5 ‰ in Japan (this study) and ∼13 ‰ recently reported in Israel or the Canary Islands indicates that spatial and temporal variation of δ34S(OCS) values is expected due to a link between anthropogenic activities and OCS cycles. The system presented herein is useful for application of δ34S(OCS) for investigation of OCS sources and sinks in the troposphere to elucidate its cycle.

Isotopic evidence for oxygenated Mesoarchaean shallow oceans

Mass-independent fractionation of sulfur isotopes (MIF-S) in Archaean sediments results from photochemical processing of atmospheric sulfur species in an oxygen-depleted atmosphere. Geological preservation of MIF-S provides evidence for microbial sulfate reduction (MSR) in low-sulfate Paleoarchaean (3.8–3.2 billion years ago (Ga)) and Neoarchaean (2.8–2.5 Ga) oceans, but the significance of MSR in Mesoarchaean (3.2–2.8 Ga) oceans is less clear. Here we present multiple sulfur and iron isotope data of early diagenetic pyrites from 2.97-Gyr-old stromatolitic dolomites deposited in a tidal flat environment of the Nsuze Group, Pongola Supergroup, South Africa. We identified consistently negative Δ33S values in pyrite, which indicates photochemical reactions under anoxic atmospheric conditions, but large mass-dependent sulfur isotope fractionations of ~30‰ in δ34S, identifying active MSR. Negative pyrite δ56Fe values (−1.31 to −0.88‰) record Fe oxidation in oxygen-bearing shallow oceans coupled with biogenic Fe reduction during diagenesis, consistent with the onset of local Fe cycling in oxygen oases ~3.0 Ga. We therefore suggest the presence of oxygenated near-shore shallow-marine environments with ≥5 μM sulfate at this time, in spite of the clear presence of an overall reduced Mesoarchaean atmosphere.

Linking Phytoplankton Activity in Polynyas and Sulfur Aerosols over Zhongshan Station, East Antarctica

Abstract Multiple year-round aerosol samplings were conducted from February 2005 to October 2008 at Zhongshan Station, a research base in East Antarctica, to study methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO42−). The concentrations of atmospheric sulfur species exhibited a seasonal cycle; the maximum and minimum concentrations occurred in austral summer and austral winter, respectively. Significant correlations between chlorophyll a (Chl a) in offshore polynyas and both MSA (r = 0.726, n = 52, and p < 0.01) and nss-SO42− (r = 0.724, n = 48, and p < 0.01) were found, indicating that the phytoplankton activity had a crucial effect on the sulfur aerosols. The sea ice dynamics in the polynyas and the variations in the polynya area may indirectly influence the sulfur aerosols in austral spring and summer. In austral winter, the sulfur compounds in the atmosphere are primarily originating in long-range transported by-products from remote regions because nearly no phytoplankton activity occurred in the offshore polynyas.

Determination of the sulfur isotope ratio in carbonyl sulfide using gas chromatography/isotope ratio mass spectrometry on fragment ions 32S+, 33S+, and 34S+.

Little is known about the sulfur isotopic composition of carbonyl sulfide (OCS), the most abundant atmospheric sulfur species. We present a promising new analytical method for measuring the stable sulfur isotopic compositions (δ(33)S, δ(34)S, and Δ(33)S) of OCS using nanomole level samples. The direct isotopic analytical technique consists of two parts: a concentration line and online gas chromatography-isotope ratio mass spectrometry (GC-IRMS) using fragmentation ions (32)S(+), (33)S(+), and (34)S(+). The current levels of measurement precision for OCS samples greater than 8 nmol are 0.42‰, 0.62‰, and 0.23‰ for δ(33)S, δ(34)S, and Δ(33)S, respectively. These δ and Δ values show a slight dependence on the amount of injected OCS for volumes smaller than 8 nmol. The isotope values obtained from the GC-IRMS method were calibrated against those measured by a conventional SF6 method. We report the first measurement of the sulfur isotopic composition of OCS in air collected at Kawasaki, Kanagawa, Japan. The δ(34)S value obtained for OCS (4.9 ± 0.3‰) was lower than the previous estimate of 11‰. When the δ(34)S value for OCS from the atmospheric sample is postulated as the global signal, this finding, coupled with isotopic fractionation for OCS sink reactions in the stratosphere, explains the reported δ(34)S for background stratospheric sulfate. This suggests that OCS is a potentially important source for background (nonepisodic or nonvolcanic) stratospheric sulfate aerosols.

Intercomparison of Clean Air Status and Trends Network Nitrate and Nitric Acid Measurements with Data from Other Monitoring Programs

The U.S. Environmental Protection Agency Clean Air Status and Trends Network (CASTNET) utilizes an open-face filter pack system to measure concentrations of atmospheric sulfur and nitrogen species. Concentration data for nitrogen species measured with filter pack systems sometimes deviate from data collected by other measurement systems used to measure the same species. The nature of these differences suggests that more than one sampling mechanism or atmospheric process is involved. The study presented here examines these differences by intercomparing CASTNET data with data from other studies, examining the results from earlier intercomparison studies, and conducting a field test to investigate the effect of particle size on filter pack measurement systems. Measurements of nitrogen species from the Maryland Aerosol Research and Characterization (MARCH) monitoring site were compared with nitrogen concentrations at three nearby CASTNET sites. Results indicate that CASTNET measured higher particulate nitrate (NO3 -) and lower gaseous nitric acid (HNO3) concentrations. Comparisons of NO3 - from 34 collocated CASTNET and Inter-agency Monitoring of Protected Visual Environments (IMPROVE) sites show that CASTNET NO3 - measurements were typically higher than the corresponding IM PROVE values. Also, results from the Lake Michigan Air Director’s Consortium Midwest Ammonia Monitoring Project demonstrated NO3 - dissociation on Teflon filters. To investigate the effect of particle size, filter pack measurement systems were operated at three CASTNET sites with and without cyclones during six 7-day measurement periods from March to August 2006. Results indicate the size-selection cyclones had a significant effect on both NO3 - and HNO3 concentrations, but little effect on sulfate (SO4 2-) and ammonium (NH4 +) levels. NO3 - concentrations sampled with the open-face filters were significantly higher than concentrations measured with a 2.5-μm cut point, as were HNO3 concentrations. Although limited in spatial and temporal coverage, the field study showed that the use of an open-face filter pack may allow for the collection of coarse NO3 - particles and for the reaction of HNO3 with metals/salts on the Teflon filter.

Attribution of modeled atmospheric sulfate and SO<sub>2</sub> in the Northern Hemisphere for June–July 1997

Abstract. Anthropogenic sulfate aerosol is a major contributor to shortwave radiative forcing of climate change by direct light scattering and by perturbing cloud properties and to local concentrations of atmospheric particulate matter. Here we analyze results from previously published calculations with an Eulerian transport model for atmospheric sulfur species in the Northern Hemisphere in June–July, 1997 to quantify the absolute and relative contributions of specific source regions (North America, Europe, and Asia) and SO2-to-sulfate conversion mechanisms (gas-phase, aqueous-phase and primary sulfate) to sulfate and SO2 column burdens as a function of location and time. Although material emitted within a given region dominates the sulfate and SO2 column burden in that region, examination of time series at specific locations shows that material imported from outside can make a substantial and occasionally dominant contribution. Frequently the major fraction of these exogenous contributions to the sulfate column burden was present aloft, thus minimally impacting air quality at the surface, but contributing substantially to the burden and, by implication, to radiative forcing and diminution of surface irradiance. Although the dominant sulfate formation pathway in the domain as a whole is aqueous-phase reaction in clouds (62%), in regions with minimum opportunity for aqueous-phase reaction gas-phase oxidation is dominant, albeit with considerable temporal variability depending on meteorological conditions. These calculations highlight the importance of transoceanic transport of sulfate, especially at the western margins of continents under the influence of predominantly westerly transport winds.

Variations of constituents of individual sea-salt particles at Syowa station, Antarctica

Sampling of atmospheric aerosol particles was carried out at Syowa station, Antarctica (39.58°E, 69.00°S) in 1998. For a better understanding of sea-salt chemistry in the coastal Antarctic regions, individual sea-salt particles were analysed using a scanning electron microscope equipped with energy dispersive X-ray spectrometer (SEM-EDX). Individual particle analysis indicates that more sea-salt particles were modified in fine particles (0.2–2 µm in diameter) through heterogeneous reactions mainly with gaseous sulfur species in the summer and reactive nitrogen oxides in the winter—spring. In particular, sea-salt particles in the coastal Antarctic atmosphere may be modified by heterogeneous reactions with not only SO2 and H2SO4 but also volatile sulfur species (e.g. CH3SO3H, DMS and DMSO) derived from bioactivity on the ocean surface during the summer. Also, low air temperature and a larger extent of sea ice offshore Syowa probably enhanced release of fractionated sea-salt particles (S-rich, Mg-rich, K-rich and Ca-rich) from the surface of snow and sea ice, particularly in September—October 1998. In addition, we attempt to estimate the scavenging rate of atmospheric sulfur species and reactive nitrogen oxides by dry deposition of sea-salt particles. Our estimation suggests that the upper limit of the scavenging rate of atmospheric sulfur species by sea-salt particles could rise to approximately 0.5 nmol m−2 day−1 at Syowa station during the summer. This value corresponded to about 30% of the concentration of particulate sulfur species such as non-sea-salt (nss)-SO2−4 and CH3SO−3 and ~10% of total atmospheric sulfur species (nss-SO2−4, CH3SO−3 and SO2). In contrast, the estimated NO−3 scavenging rate by sea-salt particles was ~0.2 nmol m−2 day−1, which is similar to the dry deposition rate of HNO3+N2O5 (approximately 0.2–0.3 nmol m−2 day−1). Hence, sea-salt particles probably play an important role as scavengers of acidic species in the coastal Antarctic regions.

Thermochemistry of atmospheric sulfur compounds

The heats of formation at 298.15 K of important atmospheric sulfur species were calculated using a high level of electronic correlation, CCSD(T), extrapolated to the complete basis set limit. Our results for SH, CH 3SH, CH 3S, CH 3SO and CH 3SO 2, are, respectively, 34.4, −5.3, 29.7, −16.8 and −53.1 kcal mol −1 . By carefully choosing the chemical reactions, this investigation reports the most accurate Δ H 0 f values available to date for these species.

Do We Understand Trends in Atmospheric Sulfur Species?

ABSTRACT Anomalies appear to exist in our understanding of atmospheric sulfur compounds, specifically as evidenced in the time trends of the different chemical forms of these compounds. Trends determined at a number of locations by several different groups seem to indicate that, responding to emission reductions across North America, the concentration of SO2 in the atmosphere is declining more rapidly than that of aerosol SO4 2-. A number of possible reasons for this discrepancy are examined, but it is not possible to provide a definitive answer at this stage. The intent is to stimulate debate, because shortcomings in our understanding of the processes involved could have profound implications for the credibility of abatement strategies and policies for both acid deposition and fine particulate matter (PM).

Evidence of atmospheric sulphur in the martian regolith from sulphur isotopes in meteorites.

Sulphur is abundant at the martian surface, yet its origin and evolution over time remain poorly constrained. This sulphur is likely to have originated in atmospheric chemical reactions, and so should provide records of the evolution of the martian atmosphere, the cycling of sulphur between the atmosphere and crust, and the mobility of sulphur in the martian regolith. Moreover, the atmospheric deposition of oxidized sulphur species could establish chemical potential gradients in the martian near-surface environment, and so provide a potential energy source for chemolithoautotrophic organisms. Here we present measurements of sulphur isotopes in oxidized and reduced phases from the SNC meteorites--the group of related achondrite meteorites believed to have originated on Mars--together with the results of laboratory photolysis studies of two important martian atmospheric sulphur species (SO2 and H2S). The photolysis experiments can account for the observed sulphur-isotope compositions in the SNC meteorites, and so identify a mechanism for producing large abiogenic 34S fractionations in the surface sulphur reservoirs. We conclude that the sulphur data from the SNC meteorites reflects deposition of oxidized sulphur species produced by atmospheric chemical reactions, followed by incorporation, reaction and mobilization of the sulphur within the regolith.

Trends in atmospheric sulfur and nitrogen species in the eastern United States for 1989–1995

Emission reductions were mandated in the Clean Air Act Amendments of 1990 with the expectation that they would result in major reductions in the concentrations of atmospherically transported pollutants. This paper investigates the form and magnitude of trends from 1989 to 1995 in atmospheric concentrations of sulfur dioxide, sulfate, and nitrogen at 34 rural sites in the eastern US. Across all sites, there is strong evidence of statistically significant declining trends in sulfur dioxide (median change of -35%) and sulfate concentrations (median change of -26%). In general, trends in nitrogen concentrations were not as pronounced (median change of -8%) as trends in the sulfur compounds. A regional estimate of trend for a cluster of sites in the Ohio River valley showed close correspondence between declining sulfur dioxide concentrations (-35%) and changes in sulfur dioxide emissions (-32%) in this region.

Atmospheric sulphur and cloud condensation nuclei in marine air in the Southern Hemisphere

Measurements of atmospheric sulphur species made in Southern Ocean air, at the Cape Grim Baseline Air Pollution Station, are reviewed in an attempt to discern the role played by oceanic emissions of dimethyl sulphide (DMS) as a source of cloud condensation nuclei (CCN). Consistent with conclusions reached by others, our data indicate that the connection between DMS concentration and CCN concentration is neither simple nor direct, being mediated through a range of chemical pathways and intermediate species that are subject to considerable variability over timescales ranging from minutes to months. Physical and meteorological processes are no less important than chemical processes as sources of complexity in the DMS to CCN transformation process. Moreover, the considerable uncertainty that currently exists about both the number of chemical pathways involved in DMS oxidation, and the kinetic coefficients associated with the proposed pathways, make quantitative modelling studies problematic. Nevertheless, synthesis of a large body of data available from Cape Grim and other Southern Ocean sites does permit some refinement of our understanding of the DMS–CCN connection. Here, these data are employed to illustrate the current state of knowledge about the connections between DMS, CCN and cloud properties at Cape Grim, and to highlight the many complexities that underlie these connections.

Atmospheric dimethylsulfide and sulfur species in aerosol and rainwater at a coastal site in New Zealand

Aspects of the atmospheric speciation of sulfur were investigated at a coastal site on the North Island of New Zealand between December 1990 and November 1992. Gaseous dimethylsulfide (DMS) as well as methanesulfonic acid (MSA) and non‐sea‐salt sulfate (NSSS) in aerosol and rainwater samples were determined. Atmospheric DMS concentrations exhibited seasonal variations in the range 0.25 nmole m−3 to 14.9 nmole m−3, with a median of 3.75 nmole m−3. Also, DMS levels varied diurnally and with meteorological variables such as wind speed and cloud coverage. Aerosol MSA concentrations similarly ranged seasonally from 0.02 to 1.40 nmole m−3 (median 0.36 nmole m−3). Aerosol NSSS concentrations varied from −1.04 to 15.9 nmole m−3, with a median value of 7.92 nmole m−3. MSA and NSSS concentrations in “clean” rainwater samples ranged from 0.03 to 0.31 μeq L−1 (median 0.04 μeq L−1) and 0.83 to 5.44 μeq L−1 (median 1.37 μeq L−1), respectively. The MSA:NSSS molar ratios varied seasonally from 0.44 to 21.4% (median 3.28%) in aerosols of marine character and from 2.38 to 22.3% (median 6.40%) for rainwater samples. Atmospheric DMS and MSA concentrations at this coastal location in New Zealand are comparable to those observed at other remote southern hemisphere sites. In contrast, NSSS concentrations are somewhat elevated, possibly incorporating an unknown contribution from heterogeneous SO2 oxidation. With respect to DMS flux calculations an oceanic emission rate of 83 mg S m−2 yr−1 would be required to account for oxidative losses (70 mg S m−2 yr−1) and leakage out of the marine boundary layer. The sum of wet and dry deposition for MSA and NSSS amounts to 65 mg S m−2 yr−1. The small difference between DMS oxidative losses and total MSA + NSSS deposition likely stems from an underestimate of the wet deposition rate for NSSS.

Sulphur and nitrogen compounds in variable marine/continental air masses at the southwest European coast

Measurements of atmospheric sulphur and nitrogen species were made on the west coast of Portugal, within the framework of BMCAPE project. Four research intensive campaigns took place between November 1993 and August 1994 and revealed pronounced seasonal cycles for DMS and MSA. Surprisingly high levels of DMS were detected during autumn (mean concentration: 776ngSm −3), possibly as a consequence of a later algae bloom or local marsh emissions. COS displayed a slight seasonal variation with mean concentrations ranging from 741 ng S m −3 in autumn up to 903 ng S m −3 in summer. On the basis of backward air mass trajectories and local meteorological data, samples were assigned into different classes of air masses. The lowest concentrations of SO 2, nssSO 4 2−, NH 3, NH 4 +, HNO 3, N0 3 − and NO 2 were found in air masses transported over the Atlantic Ocean and were about 3–10 times lower than those recorded in air masses from continental origin. Nevertheless, for many of the species, the mean concentrations in maritime air were still significantly higher than those previously recorded in remote marine sites, presumably owing to long-range transport of pollutants or contamination induced by mesoscale wind circulation.

A 3D model study of the global sulphur cycle: Contributions of anthropogenic and biogenic sources

The impact of anthropogenic emissions on the global distributions and budgets of the main atmospheric sulphur species [namely dimethylsulphide (DMS), sulphur dioxide (SO 2), and non-sea-salt (nss-) sulphates (SO 4 2−)] is investigated using the IMAGES three-dimensional. tropospheric chemistry-transport model. A previous study showed a broad consistency between modelled and observed concentrations of sulphur species for the present-day ( c. 1985) atmosphere. Here, in order to assess the relative contributions of biogenic and man-made sources, we compare distributions calculated for the preindustrial atmosphere with the present-day results. The calculations show a large increase in the concentrations of sulphur dioxide and nss-sulphates since preindustrial times, amounting to a factor of 2–3 on global average, and reaching more than two orders of magnitude at the surface in some parts of the Northern Hemisphere. Biogenic species such as DMS are also shown to be influenced by industrialization through changes in the oxidizing capacity of the atmosphere. Over the most polluted areas, the increase in sulphates deposition is found to have reached a factor of 30.

The stability of climate on Venus

The climate of Venus is to a large degree controlled by the radiative properties of its massive atmosphere. However, volcanic outgassing and surface‐atmosphere interactions may moderate the atmospheric abundances of CO2 and other radiatively important volatiles. Recently, work on the interpretation of the impact cratering record has placed limits on the magnitude of the volcanic flux. Additionally, recent laboratory data on the equilibria and kinetics of possible surface‐atmosphere reactions under Venus‐like conditions provide important insights into the role that they may play in moderating Venus' climate. The surface temperature and pressure on Venus coincide approximately with the P‐T equilibrium of the calcite‐wollastonite mineral reaction, and atmospheric sulfur species are probably involved in rapid heterogeneous reactions with the surface. Perturbations to the atmospheric inventory of radiatively active species may have a significant impact on the climate of Venus and upon the stability of the greenhouse effect. Through the use of a Venus climate model that couples atmospheric radiative‐convective equilibrium with surface processes, we show that it is likely that Venus' climate is at or near a state of unstable equilibrium. Furthermore, we show that only moderate perturbations in the abundances of radiatively active volatiles may be sufficient to precipitate changes to new climate regimes.

Distribution of atmospheric sulphur species over various wetland regions in the southeastern U.S.A.

Atmospheric dimethylsulphide (DMS), sulphur dioxide (SO 2), aerosol non-seasalt sulphate (nss-SO 4 and methanesulphonate (MSA) were measured periodically at Sapelo Island, Georgia, during March–April 1989 and April–May 1990. The spring 1990 measurements also included the sulphur gases hydrogen sulphide (H 2S), carbonyl sulphide (COS) and carbon disulphide (CS 2). In August 1989 single measurements of these compounds were also conducted in various natural environments of southern Louisiana (coastal waters, saltwater marsh, brackish/freshwater marsh, swamp). The median DMS concentration over Sapelo Island was significantly higher in April–May 1990 (92 ppt) than in March–April 1989 (18 ppt) due to enhanced biogenic DMS emission in spring. Atmospheric DMS levels increased sharply (up to 560 ppt) during advection of polluted air from paper mills located on the coastal mainland. Results obtained from measurements in Louisiana suggest that biogenic sulphur fluxes from soils and/or vegetation are significantly enhanced durign rainfall. H 2S concentrations were highly variable at each study site. Corresponding values ranged consistently higher over swamps and marshes (300–820 ppt) compared to tidal flats (3–510 ppt). Generally, DMS was the dominant biogenic sulphur gas emitted from coastal environments while further inland H 2S was the dominant species. Over all environments studied the relative contribution from natural sulphur sources to atmospheric nss-SO 4 levels ranged between approximately 15 and 50% during the individual measurement periods. Major contributions were made from regional anthropogenic sources and, on the southeastern Atlantic coast, from additional long-range transport of air masses from Africa and Europe. The effects of these sources on aerosol and rainwater acidity levels over each region are discussed.

Seasonal variations of dimethylsulfide emissions and atmospheric sulfur and nitrogen species over the western north Atlantic Ocean

Seasonal variations of dimethylsulfide emissions and atmospheric sulfur and nitrogen species over the western north Atlantic Ocean

Seasonal variations of dimethylsulfide emissions and atmospheric sulfur and nitrogen species over the western north Atlantic Ocean

Seasonal variations of dimethylsulfide emissions and atmospheric sulfur and nitrogen species over the western north Atlantic Ocean