SO2 Abundance Research Articles

Representing effects of aqueous phase reactions in shallow cumuli in global models

AbstractAqueous phase reactions are important, sometimes dominant (e.g., for SO2), pathways for the oxidation of air pollutants at the local and/or global scale. In many current chemical transport models (CTMs), the transport and aqueous reactions of chemical species are treated as split processes, and the subgrid‐scale heterogeneity between cloudy and environmental air is not considered. Here using large eddy simulation (LES) with idealized aqueous reactions mimicking the oxidation of surface‐originated SO2 by H2O2 in shallow cumuli, we show that the eddy diffusivity mass flux (EDMF) approach with a bulk plume can represent those processes quite well when entrainment/detrainment rates and eddy diffusivity are diagnosed using a conservative thermodynamic variable such as total water content. The reason is that a typical aqueous reaction such as SO2 aqueous oxidation is relatively slow compared to the in‐cloud residence time of air parcels in shallow cumuli. As a result, the surface‐originated SO2 is well correlated with and behaves like conservative thermodynamic variables that also have sources at the surface. Experiments with various reaction rate constants and relative abundances of SO2 and H2O2 indicate that when the reaction timescale approaches the in‐cloud residence time of air parcels, the errors of the bulk plume approach start to increase. Treating chemical tracer transport and aqueous reaction as split processes leads to significant errors, especially when the reaction is fast compared to the in‐cloud residence time. Overall, the EDMF approach shows large improvement over the CTM‐like treatments in matching the LES results.

Comprehensive evaluation of multi-year real-time air quality forecasting using an online-coupled meteorology-chemistry model over southeastern United States

An online-coupled meteorology-chemistry model, WRF/Chem-MADRID, has been deployed for real time air quality forecast (RT-AQF) in southeastern U.S. since 2009. A comprehensive evaluation of multi-year RT-AQF shows overall good performance for temperature and relative humidity at 2-m (T2, RH2), downward surface shortwave radiation (SWDOWN) and longwave radiation (LWDOWN), and cloud fraction (CF), ozone (O3) and fine particles (PM2.5) at surface, tropospheric ozone residuals (TOR) in O3 seasons (May-September), and column NO2 in winters (December-February). Moderate-to-large biases exist in wind speed at 10-m (WS10), precipitation (Precip), cloud optical depth (COT), ammonium (NH4+), sulfate (SO42−), and nitrate (NO3−) from the IMPROVE and SEARCH networks, organic carbon (OC) at IMPROVE, and elemental carbon (EC) and OC at SEARCH, aerosol optical depth (AOD) and column carbon monoxide (CO), sulfur dioxide (SO2), and formaldehyde (HCHO) in both O3 and winter seasons, column nitrogen dioxide (NO2) in O3 seasons, and TOR in winters. These biases indicate uncertainties in the boundary layer and cloud process treatments (e.g., surface roughness, microphysics cumulus parameterization), emissions (e.g., O3 and PM precursors, biogenic, mobile, and wildfire emissions), upper boundary conditions for all major gases and PM2.5 species, and chemistry and aerosol treatments (e.g., winter photochemistry, aerosol thermodynamics). The model shows overall good skills in reproducing the observed multi-year trends and inter-seasonal variability in meteorological and radiative variables such as T2, WS10, Precip, SWDOWN, and LWDOWN, and relatively well in reproducing the observed trends in surface O3 and PM2.5, but relatively poor in reproducing the observed column abundances of CO, NO2, SO2, HCHO, TOR, and AOD. The sensitivity simulations using satellite-constrained boundary conditions for O3 and CO show substantial improvement for both spatial distribution and domain-mean performance statistics. The model’s forecasting skills for air quality can be further enhanced through improving model inputs (e.g., anthropogenic emissions for urban areas and upper boundary conditions of chemical species), meteorological forecasts (e.g., WS10, Precip) and meteorologically-dependent emissions (e.g., biogenic and wildfire emissions), and model physics and chemical treatments (e.g., gas-phase chemistry in winter conditions, cloud processes and their interactions with radiation and aerosol).

Sulphur molecules in the circumstellar envelopes of M-type AGB stars

The sulphur compounds SO and SO$_2$ have not been widely studied in the circumstellar envelopes of asymptotic giant branch (AGB) stars. By presenting and modelling a large number of SO and SO$_2$ lines in the low mass-loss rate M-type AGB star R Dor, and modelling the available lines of those molecules in a further four M-type AGB stars, we aim to determine their circumstellar abundances and distributions. We use a detailed radiative transfer analysis based on the accelerated lambda iteration method to model circumstellar SO and SO$_2$ line emission and molecular data files for both SO and SO$_2$ that are more extensive than those previously available. Using 17 SO lines and 98 SO2 lines to constrain our models for R Dor, we find an SO abundance of 6.7x10$^{-6}$ and an SO$_2$ abundance of 5x10$^{-6}$ with both species having high abundances close to the star. We also modelled $^{34}$SO and found an abundance of 3.1x10$^{-7}$, giving an $^{32}$SO/$^{34}$SO ratio of 21.6. We derive similar results for the circumstellar SO and SO$_2$ abundances and their distributions for the low mass-loss rate object W Hya. For these stars, the circumstellar SO and SO$_2$ abundances are much higher than predicted by chemical models and these two species may account for all available sulphur. For the higher mass-loss rate stars, we find shell-like SO distributions with peak abundances that decrease and peak abundance radii that increase with increasing mass-loss rate. The positions of the peak SO abundance agree very well with the photodissociation radii of H$_2$O. We find evidence that SO is most likely through the photodissociation of H$_2$O and the subsequent reaction between S and OH. The S-bearing parent molecule appears not to be H$_2$S. The SO$_2$ models suggest an origin close to the star for this species, also disagreeing with current chemical models.

Sgr B2(N): A BIPOLAR OUTFLOW AND ROTATING HOT CORE REVEALED BY ALMA

We present the results of SiO (2-1) and SO2 (12-13) line observations of Sgr B2(N) made with the Atacama Large Millimeter/submillimeter Array (ALMA) at an angular resolution of ~2arcsec. Our analysis of the SiO and SO2 line emission reveals a bipolar molecular outflow in an east-west direction whose driving source is located at K2. In addition, SO2 line core shows a north-south velocity gradient most probably indicating a hot core of molecular gas rotating around K2. Fractional abundances of SO2 and SiO (X(SO2) and X(SiO), respectively) in the outflowing molecular gas are derived from comparisons with the C18O emission. Assuming an excitation temperature of 100+-50 K, we calculate X(SO2) = 2.3X10^-8 and X(SiO) = 1.2X10^-9. The outflow from SgrB2(N) K2 is characterized as a young (5X10^3yr) and massive (~2000Msun), but moderately collimated (~60deg) outflow. We also report a possible detection of the SiO (v=2, J=2-1) maser emission from the position of K2. If confirmed, it would make Sgr B2(N) the 4th star forming region associated with SiO masers.

The jet and the disk of the HH 212 low-mass protostar imaged by ALMA: SO and SO2emission

To investigate the disk formation and jet launch in protostars is crucial to comprehend the earliest stages of star and planet formation. We aim to constrain the properties of the molecular jet and the disk of the HH 212 protostellar system at unprecedented angular scales through ALMA observations of sulfur-bearing molecules, SO 9(8)-8(7), SO 10(11)-10(10), SO2 8(2,6)-7(1,7). SO 9(8)-8(7) and SO2 8(2,6)-7(1,7) show broad velocity profiles. At systemic velocity they probe the circumstellar gas and the cavity walls. Going from low to high blue-/red-shifted velocities the emission traces the wide-angle outflow and the fast (~100-200 km/s) and collimated (~90 AU) molecular jet revealing the inner knots with timescales <50 years. The jet transports a mass loss rate >0.2-2e-6 Msun/yr, implying high ejection efficiency (>0.03-0.3). The SO and SO2 abundances in the jet are ~1e-7-1e-6. SO 10(11)-10(10) emission is compact and shows small-scale velocity gradients indicating that it originates partly from the rotating disk previously seen in HCO+ and C17O, and partly from the base of the jet. The disk mass is >0.002-0.013 Msun, and the SO abundance in the disk is ~1e-8-1e-7. SO and SO2 are effective tracers of the molecular jet in the inner few hundreds AU from the protostar. Their abundances indicate that 1% - 40% of sulfur is in SO and SO2 due to shocks in the jet/outflow and/or to ambipolar diffusion at the wind base. The SO abundance in the disk is 3-4 orders of magnitude larger than in evolved protoplanetary disks. This may be due to an SO enhancement in the accretion shock at the envelope-disk interface or in spiral shocks if the disk is partly gravitationally unstable.

Incorporating an advanced aerosol activation parameterization into WRF‐CAM5: Model evaluation and parameterization intercomparison

AbstractAerosol activation into cloud droplets is an important process that governs aerosol indirect effects. The advanced treatment of aerosol activation by Fountoukis and Nenes (2005) and its recent updates, collectively called the FN series, have been incorporated into a newly developed regional coupled climate‐air quality model based on the Weather Research and Forecasting model with the physics package of the Community Atmosphere Model version 5 (WRF‐CAM5) to simulate aerosol‐cloud interactions in both resolved and convective clouds. The model is applied to East Asia for two full years of 2005 and 2010. A comprehensive model evaluation is performed for model predictions of meteorological, radiative, and cloud variables, chemical concentrations, and column mass abundances against satellite data and surface observations from air quality monitoring sites across East Asia. The model performs overall well for major meteorological variables including near‐surface temperature, specific humidity, wind speed, precipitation, cloud fraction, precipitable water, downward shortwave and longwave radiation, and column mass abundances of CO, SO2, NO2, HCHO, and O3 in terms of both magnitudes and spatial distributions. Larger biases exist in the predictions of surface concentrations of CO and NOx at all sites and SO2, O3, PM2.5, and PM10 concentrations at some sites, aerosol optical depth, cloud condensation nuclei over ocean, cloud droplet number concentration (CDNC), cloud liquid and ice water path, and cloud optical thickness. Compared with the default Abdul‐Razzack Ghan (2000) parameterization, simulations with the FN series produce ~107–113% higher CDNC, with half of the difference attributable to the higher aerosol activation fraction by the FN series and the remaining half due to feedbacks in subsequent cloud microphysical processes. With the higher CDNC, the FN series are more skillful in simulating cloud water path, cloud optical thickness, downward shortwave radiation, shortwave cloud forcing, and precipitation. The model evaluation identifies several areas of improvements including emissions and their vertical allocation as well as model formulations such as aerosol formation, cloud droplet nucleation, and ice nucleation.

Application of WRF/Chem over East Asia: Part I. Model evaluation and intercomparison with MM5/CMAQ

Abstract In this work, the application of the online-coupled Weather Research and Forecasting model with chemistry (WRF/Chem) version 3.3.1 is evaluated over East Asia for January, April, July, and October 2005 and compared with results from a previous application of an offline model system, i.e., the Mesoscale Model and Community Multiple Air Quality modeling system (MM5/CMAQ). The evaluation of WRF/Chem is performed using multiple observational datasets from satellites and surface networks in mainland China, Hong Kong, Taiwan, and Japan. WRF/Chem simulates well specific humidity (Q2) and downward longwave and shortwave radiation (GLW and GSW) with normalized mean biases (NMBs) within 24%, but shows moderate to large biases for temperature at 2-m (T2) (NMBs of −9.8% to 75.6%) and precipitation (NMBs of 11.4–92.7%) for some months, and wind speed at 10-m (WS10) (NMBs of 66.5–101%), for all months, indicating some limitations in the YSU planetary boundary layer scheme, the Purdue Lin cloud microphysics, and the Grell–Devenyi ensemble scheme. WRF/Chem can simulate the column abundances of gases reasonably well with NMBs within 30% for most months but moderately to significantly underpredicts the surface concentrations of major species at all sites in nearly all months with NMBs of −72% to −53.8% for CO, −99.4% to −61.7% for NOx, −84.2% to −44.5% for SO2, −63.9% to −25.2% for PM2.5, and −68.9% to 33.3% for PM10, and aerosol optical depth in all months except for October with NMBs of −38.7% to −16.2%. The model significantly overpredicts surface concentrations of O3 at most sites in nearly all months with NMBs of up to 160.3% and NO 3 - at the Tsinghua site in all months. Possible reasons for large underpredictions include underestimations in the anthropogenic emissions of CO, SO2, and primary aerosol, inappropriate vertical distributions of emissions of SO2 and NO2, uncertainties in upper boundary conditions (e.g., for O3 and CO), missing or inaccurate model representations (e.g., secondary organic aerosol formation, gas/particle partitioning, dust emissions, dry and wet deposition), and inaccurate meteorological fields (e.g., overpredictions in WS10 and precipitation, but underpredictions in T2), as well as the large uncertainties in satellite retrievals (e.g., for column SO2). Comparing to MM5, WRF generally gives worse performance in meteorological predictions, in particular, T2, WS10, GSW, GLW, and cloud fraction in all months, as well as Q2 and precipitation in January and October, due to limitations in the above physics schemes or parameterizations. Comparing to CMAQ, WRF/Chem performs better for surface CO, O3, and PM10 concentrations at most sites in most months, column CO and SO2 abundances, and AOD. It, however, gives poorer performance for surface NOx concentrations at most sites in most months, surface SO2 concentrations at all sites in all months, and column NO2 abundances in January and April. WRF/Chem also gives lower concentrations of most secondary PM and black carbon. Those differences in results are attributed to differences in simulated meteorology, gas-phase chemistry, aerosol thermodynamic and dynamic treatments, dust and sea salt emissions, and wet and dry deposition treatments in both models.

Submarine venting of magmatic volatiles in the Eastern Manus Basin, Papua New Guinea

The SuSu Knolls and DESMOS hydrothermal fields are located in the back-arc extensional transform zone of the Eastern Manus Basin. In 2006, highly acidic and ΣSO4-rich vent fluids were collected at both sites and analyzed for the chemical and isotopic composition of major and trace species. Fluids exiting the seafloor have measured temperatures from 48 to 215°C and are milky white in appearance due to precipitation of elemental S0. Vent fluid concentrations of Na, K, and Mg are depleted by as much as 30% relative to seawater, but have the same relative abundance. In contrast, the fluids are highly enriched in dissolved ΣCO2, Cl, SiO2(aq), Fe, and Al relative to seawater. Measured pH (25°C) ranged from 0.95 to 1.87 and aqueous ΣSO4 ranged from 35 to 135mmol/kg. The chemical and isotopic composition points to formation via subsurface mixing of seawater with a Na-, K-, Mg-, and Ca-free, volatile-rich magmatic fluid exsolved from subsurface magma bodies during a process analogous to subaerial fumarole discharge. Estimates of the magmatic end-member composition indicate a fluid phase where H2O>SO2>CO2≈Cl>F. The hydrogen and oxygen isotopic composition of H2O and carbon isotopic composition of ΣCO2 in the vent fluids strongly suggest a contribution of slab-derived H2O and CO2 to melts generated in the mantle beneath the Eastern Manus volcanic zone. Abundant magmatically-derived SO2 undergoes disproportionation during cooling in upflow zones and contributes abundant acidity, SO42−, and S0 to the venting fluids. Interaction of these highly acidic fluids with highly altered mineral assemblages in the upflow zone are responsible for extensive aqueous mobilization of SiO2(aq), Fe, and Al. Temporal variability in the speciation and abundance of aqueous S species between 1995 and 2006 at the DESMOS vent field suggests an increase in the relative abundance of SO2 in the magmatic end-member that has mixed with seawater in the subsurface. Results of this study constrain processes responsible for the formation of hot-spring fluids in magmatically active back-arc environments and the resulting chemical exchange between the lithosphere and water column.

Submillimeter mapping of mesospheric minor species on Venus with ALMA

Millimeter and submillimeter heterodyne spectroscopy offers the possibility of probing the mesosphere of Venus and monitoring minor species and winds. ALMA presents a unique opportunity to map mesospheric species of Venus. During Cycle 0, we have observed Venus on November 14 and 15, 2011, using the compact configuration of ALMA. The diameter of Venus was 11″ and the illumination factor was about 90%. Maps of CO, SO, SO2 and HDO have been built from transitions recorded in the 335–347GHz frequency range. A mean mesospheric thermal profile has been inferred from the analysis of the CO transition at the disk center, to be used in support of minor species retrieval. Maps of SO and SO2 abundance show significant local variations over the disk and contrast variations by as much as a factor 4. In the case of SO2, the spatial distribution appears more “patchy”, i.e. shows short-scale structures apparently disconnected from day-side and latitudinal variations. For both molecules, significant changes occur over a timescale of one day. From the disk averaged spectrum of SO recorded on November 14 at 346.528GHz, we find that the best fit is obtained with a cutoff in the SO vertical distribution at 88±2km and a uniform mixing ratio of 8.0±2.0ppb above this level. The SO2 map of November 14, derived from the weaker transition at 346.652GHz, shows a clear maximum in the morning side at low latitudes, which is less visible in the map of November 15. We find that the best fit for SO2 is obtained for a cutoff in the vertical distribution at 88±3km and a uniform mixing ratio of 12.0±3.5ppb above this level. The HDO maps retrieved from the 335.395GHz show some enhancement in the northern hemisphere, but less contrasted variations than for the sulfur species maps, with little change between November 14 and 15. Assuming a typical D/H ratio of 200 times the terrestrial value in the mesosphere of Venus, we find that the disk averaged HDO spectrum is best fitted with a uniform H2O mixing ratio of 2.5±0.6ppm (corresponding to a HDO mixing ratio of 0.165±0.040ppm). We note that our spectrum is also compatible with a H2O mixing ratio of 1.5ppm in the 80–90km altitude range, and a mixing ratio of 3ppm outside this range, as suggested by the photochemical model of Zhang et al. (2012, Icarus, vol. 217, pp. 714–739). Our results are in good general agreement with previous single dish submillimeter observations of Sandor and Clancy (2005, Icarus, vol. 177, pp. 129–143), Gurwell et al. (2007, Icarus, vol. 188, p. 288), and Sandor et al. (2010, Icarus, vol. 208, pp. 49–60; 2012, Icarus, vol. 217, pp. 839–844 ) and with SPICAV/Venus Express results of Fedorova et al. (2008, J. Geophys. Res., vol. 113, p. E00B25) and Belyaev et al. (2012).

Long-term variations of the UV contrast on Venus observed by the Venus Monitoring Camera on board Venus Express

We analyze the Venus ultraviolet (UV) reflectivity as observed by the Venus Monitoring Camera on board Venus Express over 2000 orbits in the years 2006–2011. We compare several laws for the photometric correction of global images of Venus, and find that the combined law of Lambert and Lommel-Seeliger is most suitable for our study. Our analysis of the corrected images reveals strong fluctuations in the reflectivity contrast between low and high latitude regions of up to 40%, that follow variations of the SO2 abundance above the cloud top. Additionally, the phase angle dependence of the contrast gradually change from weak to strong, which may be related with the vertical distribution of the unknown UV absorber and the overlaying upper haze layer. We suggest that these variations result from a combination of two processes. One is the meridional transport of SO2, which forms sulfuric acid aerosol particles at high latitudes. The other is the presence of vertical winds near the cloud top level, which control the vertical mixing of the unknown UV absorber and the upper haze.

Evolution of the 2011 Mt. Etna ash and SO2 lava fountain episodes using SEVIRI data and VPR retrieval approach

In this paper an estimation is made of the temporal evolution of volcanic ash and sulfur dioxide (SO2) emissions from Mt. Etna during its eruption phases. The retrieval is performed using MSG-SEVIRI (Meteosat Second Generation — Spinning Enhanced Visible and Infra Red Imager) images in the TIR (Thermal InfraRed) spectral range. The ash and SO2 plume abundance maps are computed using the Volcanic Plume Removal (VPR) procedure originally applied to MODIS (Moderate Resolution Imaging Spectroradiometer) sensors on board the NASA Terra and Aqua satellites. As test cases, two 2011 lava fountain episodes were considered. The set of parameters required by VPR for the Mt. Etna volcano, Volz type particles, and the SEVIRI sensor are presented. Once the parameters have been computed, the VPR approach requires as input only the SEVIRI-TIR radiances of the bands centered at 8.7, 10.8, and 12.0μm, together with the plume temperature and altitude. The VPR returns maps of plume particles' effective radius, aerosol optical depth at 550nm, and columnar abundance of ash and SO2. A new procedure for estimating wind speed and direction is also presented. Since the ash and SO2 abundance maps, and wind speed at the plume altitude are known, it is possible to reconstruct the ash and SO2 fluxes emitted during the eruption through time. The VPR procedure, applied to TIR SEVIRI data, allows for fast and reliable ash and SO2 retrieval with high temporal resolution during both day and night, and is thus suitable for operational use during a volcanic crisis.

Lower atmosphere minor gas abundances as retrieved from Venus Express VIRTIS-M-IR data at 2.3 µm

Minor gas abundances in the lower atmosphere of Venus׳ southern hemisphere are investigated using spectroscopic nightside measurements recorded by the Visible and InfraRed Thermal Imaging Spectrometer aboard ESA’s Venus Express mission in the moderate spectral resolution infrared mapping channel (VIRTIS-M-IR, 1–5µm, FWHM=17nm). The entire usable data archive is utilized including only radiation spectra sampled at long detector exposure times (≥3.3s) during eight Venus solar days between April 2006 and October 2008. Combined radiative transfer and retrieval techniques (Haus et al., 2013; Haus et al., 2014) are applied for a simultaneous determination of total cloud opacity and H2O, CO, and OCS abundances from the 2.3µm atmospheric transparency window that sounds the altitude range between about 30 and 45km. A wavelength-dependent CO2 opacity correction is considered.Zonal averages of CO abundances at 35km increase by about 35% from (22.9±0.8) ppmv at equatorial latitudes to (31.0±2.1) ppmv at 65°S and then decrease to (29.4±2.4) ppmv at 80°S The±figures refer to the statistical variability of retrieved abundances. In accordance with earlier results, the observed latitudinal variation of tropospheric CO is consistent with a Hadley cell-like circulation. Dawn side CO abundances at high latitudes are slightly smaller than dusk side values by about 7%. The latitudinal distribution of OCS at 35km is anticorrelated with that of CO, ranging from about (1.15±0.2) ppmv at 65°S to (1.60±0.2) ppmv at low latitudes (poleward decrease of 28%). Zonal averages of H2O abundances near 35km slightly decrease toward the South Pole by about 10%, and the hemispheric average is (32.0±1.3) ppmv. A significant local time dependence of OCS and H2O is not observed. Detailed analyses of individual spectrum retrieval errors for different atmospheric models reveal that CO abundance results are reliable (error 4–7%), while H2O and OCS results have lower confidence (errors 30–47% and 41–86%, respectively). SO2 abundances cannot reliably be retrieved from VIRTIS-M-IR spectra.

Venus’ clouds as inferred from the phase curves acquired by IR1 and IR2 on board Akatsuki

We present phase curves for Venus in the 1–2μm wavelength region, acquired with IR1 and IR2 on board Akatsuki (February–March 2011). A substantial discrepancy with the previously-published curves was found in the small phase angle range (0–30°). Through analysis by radiative-transfer computation, it was found that the visibility of larger (∼1μm or larger) cloud particles was significantly higher than in the standard cloud model. Although the cause is unknown, this may be related to the recently reported increase in the abundance of SO2 in the upper atmosphere. It was also found that the cloud top is located at ∼75km and that 1-μm particles exist above the cloud, both of these results being consistent with recent studies based on the Venus Express observations in 2006–2008. Further monitoring, including photometry for phase curves, polarimetry for aerosol properties, spectroscopy for SO2 abundance, and cloud opacity measurements in the near-infrared windows, is required in order to understand the mechanism of this large-scale change.

SULFUR- AND SILICON-BEARING MOLECULES IN PLANETARY NEBULAE: THE CASE OF M2-48

Molecular-line observations of the bipolar planetary nebula (PN) M2-48 have been conducted using the Sub-Millimeter Telescope and the 12 m antenna of the Arizona Radio Observatory at 1, 2, and 3 mm. M2-48 is estimated to be ~4800 yr old, midway through the PN evolutionary track. SiO and SO2 were detected in this source—the first identification of either molecule in a PN. CN, HCN, HNC, CS, SO, HCO+, N2H+, and several 13C isotopologues such as 13CN, H13CN, and H13CO+ were also observed toward this object. A radiative transfer analysis of multiple SiO transitions indicates a gas kinetic temperature of T K ~ 55 K and a density of n(H2) ~ 9 × 105 cm–3 in M2-48, in agreement with previous CS and CO modeling. After CO, CN, and SO were found to be the most prevalent molecules in this nebula, with fractional abundances, relative to H2, of f ~ 3.8 × 10–7 and 2.4 × 10–7, respectively. SO2 and HCN are also abundant, with f ~ 1.2 × 10–7, indicating an [SO]/[SO2] ratio of ~2. Relatively high ion abundances were measured in M2-48 as well, with f ~ 10–7 for both HCO+ and N2H+. An [HCN]/[HNC] ratio of ~2 was determined, as typically observed in other PNe, independent of age. The high abundances of SO and SO2, along with the presence of SiO with f ~ 2.9 × 10–8, suggest O/C > 1 in this source; furthermore, the prevalence of CN and N2H+ indicates nitrogen enrichment. The 12C/13C ratio of ~3 in the nebula was also established. These factors indicate hot-bottom burning occurred in the progenitor star of M2-48, suggesting an initial mass > 4 M ☉.

Reactive halogens (BrO and OClO) detected in the plume of Soufrière Hills Volcano during an eruption hiatus

AbstractVolcanic plumes are sites of dynamic chemistry involving halogen gases. Here we present new data on the relative abundances of SO2, BrO and OClO gases emitted from Soufrière Hills Volcano [SHV). They were collected during an eruptive hiatus but during sustained degassing at this halogen‐rich volcano. By comparison with data from a previous study during an eruptive phase and application of the data and modeling of Villemant et al. (2008), we suggest that, after consideration of errors, either the rate of HBr conversion to BrO is variable, ranging from ∼30% to ∼15%, and/or the relative partitioning of Cl and Br into the gas phase from the melt changes according to eruptive activity. We examine the potential implications of this for fluid‐melt partitioning, and compare our results with data from the experimental literature. Our work contributes toward understanding the controls on the BrO/SO2 ratio for volcano monitoring purposes; the changes in plume chemistry with regard to bromine at the onset of lava extrusion may be large and rapid. OClO was detected in the plume at SHV for the first time. This species has only previously been detected in emissions from Mount Etna (using ground‐based methods) and from Puyehue Cordon Caulle (using satellite‐based methods). No HCHO or NOy species were detected in the spectra.

A multi-model assessment for the 2006 and 2010 simulations under the Air Quality Model Evaluation International Initiative (AQMEII) Phase 2 over North America: Part II. Evaluation of column variable predictions using satellite data

Within the context of the Air Quality Model Evaluation International Initiative Phase 2 (AQMEII2) project, this part II paper performs a multi-model assessment of major column abundances of gases, radiation, aerosol, and cloud variables for 2006 and 2010 simulations with three online-coupled air quality models over the North America using available satellite data. It also provides the first comparative assessment of the capabilities of the current generation of online-coupled models in simulating column variables. Despite the use of different model configurations and meteorological initial and boundary conditions, most simulations show comparable model performance for many variables. The evaluation results show an excellent agreement between all simulations and satellite-derived radiation variables including downward surface solar radiation, longwave radiation, and top-of-atmospheric outgoing longwave radiation, as well as precipitable water vapor with domain-average normalized mean biases (NMBs) of typically less than 5% and correlation coefficient (R) typically more than 0.9. Most simulations perform well for column-integrated abundance of CO with domain-average NMBs of −9.4% to −2.2% in 2006 and −12.1% to 4.6% in 2010 and from reasonably well to fair for column NO2, HCHO, and SO2, with domain-average NMBs of −37.7% to 2.1%, −27.3% to 59.2%, and 16.1% to 114.2% in 2006, respectively, and, 12.9% to 102.1%, −25.0% to 87.6%, −65.2% to 7.4% in 2010, respectively. R values are high for CO and NO2 typically between 0.85 and 0.9 (i.e., R2 of 0.7–0.8). Tropospheric ozone residuals are overpredicted by all simulations due to overestimates of ozone profiles from boundary conditions. Model performance for cloud-related variables is mixed and generally worse compared to gases and radiation variables. Cloud fraction (CF) is well reproduced by most simulations. Other aerosol/cloud related variables such as aerosol optical depth (AOD), cloud optical thickness, cloud liquid water path, cloud condensation nuclei, and cloud droplet number concentration (CDNC) are moderately to largely underpredicted by most simulations, due to underpredictions of aerosol loadings and also indicating high uncertainties associated with the current model treatments of aerosol–cloud interactions and the need for further model development. Negative correlations are found for AOD for most simulations due to large negative biases over the western part of the domain. Inter-model discrepancies also exist for a few variables such as column abundances of HCHO and SO2 and CDNC due likely to different chemical mechanisms, biogenic emissions, and treatments of aerosol indirect effects. Most simulations can also capture the inter-annual trend observed by satellites between 2006 and 2010 for several variables such as column abundance of NO2, AOD, CF, and CDNC. Results shown in this work provide the important benchmark for future online-couple air quality model development.

Electrochemical sensors applied to pollution monitoring: Measurement error and gas ratio bias — A volcano plume case study

There is an increasing scientific interest in the use of miniature electrochemical sensors to detect and quantify atmospheric trace gases. This has led to the development of ‘Multi-Gas’ systems applied to measurements of both volcanic gas emissions, and urban air pollution. However, such measurements are subject to uncertainties introduced by sensor response time, a critical issue that has received limited attention to date. Here, a detailed analysis of output from an electrochemical SO2 sensor and two H2S sensors (contrasting in their time responses and cross-sensitivities) demonstrates how instrument errors arise under the conditions of rapidly fluctuating (by dilution) gas abundances, leading to scatter and importantly bias in the reported gas ratios. In a case study at Miyakejima volcano (Japan), electrochemical sensors were deployed at both the crater-rim and downwind locations, thereby exposed to rapidly fluctuating and smoothly varying plume gas concentrations, respectively. Discrepancies in the H2S/SO2 gas mixing ratios derived from these measurements are attributed to the sensors' differing time responses to SO2 and H2S under fluctuating plume conditions, with errors magnified by the need to correct for SO2 interference in the H2S readings. Development of a sensor response model that reproduces sensor t90 behaviour (the time required to reach 90% of the final signal following a step change in gas abundance) during calibration enabled this measurement error to be simulated numerically. The sensor response times were characterised as SO2 sensor (t90~13s), H2S sensor without interference (t90~11s), and H2S sensor with interference (t90~20s to H2S and ~32s to SO2). We show that a method involving data integration between periods of episodic plume exposure identifiable in the sensor output yields a less biased H2S/SO2 ratio estimate than that derived from standard analysis approaches. For the Miyakejima crater-rim dataset this method yields highly correlated H2S and SO2 abundances (R2>0.99) and the improved crater-rim data analysis combined with downwind measurements yields H2S/SO2=0.11±0.01. Our analysis has significant implications for the reliance that can be placed on ‘Multi-Gas’-derived gas ratios, whether for volcanological or other purposes, in the absence of consideration of the complexities of sensor response times.

Applying UV cameras for SO2 detection to distant or optically thick volcanic plumes

Ultraviolet (UV) camera systems represent an exciting new technology for measuring two dimensional sulfur dioxide (SO2) distributions in volcanic plumes. The high frame rate of the cameras allows the retrieval of SO2 emission rates at time scales of 1Hz or higher, thus allowing the investigation of high-frequency signals and making integrated and comparative studies with other high-data-rate volcano monitoring techniques possible. One drawback of the technique, however, is the limited spectral information recorded by the imaging systems. Here, a framework for simulating the sensitivity of UV cameras to various SO2 distributions is introduced. Both the wavelength-dependent transmittance of the optical imaging system and the radiative transfer in the atmosphere are modeled. The framework is then applied to study the behavior of different optical setups and used to simulate the response of these instruments to volcanic plumes containing varying SO2 and aerosol abundances located at various distances from the sensor. Results show that UV radiative transfer in and around distant and/or optically thick plumes typically leads to a lower sensitivity to SO2 than expected when assuming a standard Beer–Lambert absorption model. Furthermore, camera response is often non-linear in SO2 and dependent on distance to the plume and plume aerosol optical thickness and single scatter albedo. The model results are compared with camera measurements made at Kilauea Volcano (Hawaii) and a method for integrating moderate resolution differential optical absorption spectroscopy data with UV imagery to retrieve improved SO2 column densities is discussed.

A new simplified approach for simultaneous retrieval of SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and ash content of tropospheric volcanic clouds: an application to the Mt Etna volcano

Abstract. A new procedure is presented for simultaneous estimation of SO2 and ash abundance in a volcanic plume, using thermal infrared (TIR) MODIS data. Plume altitude and temperature are the only two input parameters required to run the procedure, while surface emissivity, temperature, atmospheric profiles, ash optical properties, and radiative transfer models are not necessary to perform the atmospheric corrections. The procedure gives the most reliable results when the surface under the plume is uniform, for example above the ocean, but still produces fairly good estimates in more challenging and not easily modelled conditions, such as above land or meteorological cloud layers. The developed approach was tested on the Etna volcano. By linearly interpolating the radiances surrounding a detected volcanic plume, the volcanic plume removal (VPR) procedure described here computes the radiances that would have been measured by the sensor in the absence of a plume, and reconstructs a new image without plume. The new image and the original data allow computation of plume transmittance in the TIR-MODIS bands 29, 31, and 32 (8.6, 11.0 and 12.0 μm) by applying a simplified model consisting of a uniform plume at a fixed altitude and temperature. The transmittances are then refined with a polynomial relationship obtained by means of MODTRAN simulations adapted for the geographical region, ash type, and atmospheric profiles. Bands 31 and 32 are SO2 transparent and, from their transmittances, the effective ash particle radius (Re), and aerosol optical depth at 550 nm (AOD550) are computed. A simple relation between the ash transmittances of bands 31 and 29 is demonstrated and used for SO2 columnar content (cs) estimation. Comparing the results of the VPR procedure with MODTRAN simulations for more than 200 000 different cases, the frequency distribution of the differences shows the following: the Re error is less than ±0.5 μm in more than 60% of cases; the AOD550 error is less than ±0.125 in 80% of cases; the cs error is less than ±0.5 g m−2 in more than 60% of considered cases. The VPR procedure was applied in two case studies of recent eruptions occurring at the Mt Etna volcano, Italy, and successfully compared with the results obtained from the established SO2 and ash assessments based on look-up tables (LUTs). Assessment of the sensitivity to the plume altitude uncertainty is also made. The VPR procedure is simple, extremely fast, and can be adapted to other ash types and different volcanoes.

The chemical compositions and abundances of volatiles in the Siberian large igneous province: Constraints on magmatic CO2 and SO2 emissions into the atmosphere

The Siberian large igneous province (SLIP) is known to be synchronous with the most severe mass extinction on the Earth at the end of Permian. The viability of the SLIP as a trigger for the mass extinction depends crucially on the total amounts of important volatiles such as CO2 and SO2 emitted from the SLIP into the atmosphere. The chemical compositions and abundances of volatiles in picrite and gabbroic rocks of the SLIP have been determined by a vacuum stepwise heating mass spectrometer system. The volatiles released at temperatures <400°C from mineral separates are interpreted to derive from secondary fluid inclusions and are therefore not included in the summation of primary volatiles which had been primarily entrapped in the minerals from magma. The primary volatiles released from different types of samples from the SLIP are characterized by dominant H2O with high contents of CO2, SO2 and H2, plus detectable He. The total amounts of primary volatiles in the picrite are 19,991mm3.STP/g (STP-standard temperature and pressure) H2O, 331 CO2, 202 H2, 28 CO, 13 SO2 and 2 H2S. The total amounts of primary volatiles in the gabbroic rocks are 2869mm3.STP/g H2O, 131 SO2, 120 H2, 85 CO2, 79 H2S and 16 CO. These data, together with other important constraints from literatures, are used to calculate the total amounts of volatiles emitted from the SLIP into the atmosphere. In our mass balance calculations we used the abundances of CO2 and SO2 in melt inclusions in olivine phenocrysts from the SLIP determined previously by other researchers to represent their initial concentrations in magma before degassing, and our new data for the SLIP picrite to represent the volatile compositions of magma (basalt) after eruption. Our results for the gabbroic rocks are used to estimate the proportions of volatiles that are still retained in the subvolcanic intrusions of the SLIP. The results reveal that the total amounts of important volatiles emitted from the SLIP are 8.5×107 Tg CO2, 4.4×106 Tg CO, 7.0×106 Tg H2S and 6.8×107 Tg SO2 (Tg, Trillion grams). These values are similar to the previous estimates using different methods by other researchers. Our data support a popular notion that the end-Permian mass extinction on the Earth was caused by the emission of enormous amounts of volatiles from the SLIP into the atmosphere.