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All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

A simulation of the Cerro Hudson SO2 cloud

An isentropic trajectory model is used to simulate the evolution of the southern hemisphere SO2 cloud associated with the eruption of Cerro Hudson. By matching the parcel trajectories with total ozone mapping spectrometer SO2 retrievals, the principal stratospheric injection region is determined to be between 11 and 16 km in altitude. This region is characterized by weak wind shears and is located just poleward of the subtropical jet in the outer fringe of the stratospheric polar vortex. The lack of wind shear in the injection region explains the slow zonal dispersal of the SO2 cloud which was still clearly observed 19 days after the eruption. The trajectory model simulation of the SO2 cloud shows good agreement with observations for 7 days after the eruption. Using the potential vorticity and potential temperature estimates of the initial eruption cloud, the cloud position relative to the polar night jet is shown to be nearly fixed up to September 2, 1991, which was as long as the cloud was observed. This result suggests that the lower stratospheric polar and midlatitude regions are nearly isolated from each other during the late August period.

Schoeberl, Mark R.↗
NASA NTRS1993

Model simulations of the competing climatic effects of SO2 and CO2

Sulfur dioxide-derived cloud condensation nuclei are expected to enhance the planetary albedo, thereby cooling the planet. This effect might counteract the global warming expected from enhanced greenhouse gases. A detailed treatment of the relationship between fossil fuel burning and the SO2 effect on cloud albedo is implemented in a two-dimensional model for assessing the climate impact. Using a conservative approach, results show that the cooling induced by the SO2 emission can presently counteract 50 percent of the CO2 greenhouse warming. Since 1980, a strong warming trend has been predicted by the model: 0.15 C during the 1980-1990 period alone. The model predicts that by the year 2060 the SO2 cooling reduces climate warming by 0.5 C or 25 percent for the Intergovernmental Panel on Climate Change (IPCC) business as usual (BAU) scenario and 0.2 C or 20 percent for scenario D (for a slow pace of fossil fuel burning). The hypothesis is examined that the different responses between the Northern Hemisphere and the Southern Hemisphere can be used to validate the presence of the SO2-induced cooling.

Kaufman, Yoram J.↗
NASA NTRS1993

The condensation and vaporization behavior of ices containing SO2, H2S, and CO2: Implications for Io

In an extension of previously reported work on ices containing CO, CO2, H2O, CH3OH, NH3, and H2, measurements of the physical and infrared spectral properties of ices containing molecules relevant to Jupiter's moon Io are presented. These include studies on ice systems containing SO2, H2S, and CO2. The condensation and sublimation behaviors of each ice system and surface binding energies of their components are discussed. The surface binding energies can be used to calculate the residence times of the molecules on a surface as a function of temperature and thus represent important parameters for any calculation that attempts to model the transport of these molecules on Io's surface. The derived values indicate that SO2 frosts on Io are likely to anneal rapidly, resulting in less fluffy, 'glassy' ices and that H2S can be trapped in the SO2 ices of Io during night-time hours provided that SO2 deposition rates are on the order of 5 micrometers/hr or larger.

Sandford, Scott A.↗
NASA NTRS1994

On Io's 2.788-micron band: Origin by SO2 or H2O?

Laboratory reflectance spectra of SO2 frost and ice and thin H2O frost show that the recently reported band at 2.788 microns in Io's disk-integrated spectrum can be qualitatively explained by the presence of solid SO2 on Io's surface. However, the reported width of the Io band is too great to be explained by SO2 frost or ice alone. Lab spectra presented here, and other data cited here, show clearly that solid SO2 has a strong band at 2.789 microns, and that Io should have such a band. These results do not support the claim of Bregman et al. that H2O is the primary cause of the Io band.

Nash, Douglas B.↗
NASA NTRS1997

CO2 greenhouse in the early martian atmosphere: SO2 inhibits condensation

Many investigators of the early martian climate have suggested that a dense carbon dioxide atmosphere was present and warmed the surface above the melting point of water (J.B. Pollack, J.F. Kasting, S.M. Richardson, and K. Poliakoff 1987. Icarus 71, 203-224). However, J.F. Kasting (1991. Icarus 94, 1-13) pointed out that previous thermal models of the primitive martian atmosphere had not considered the condensation of CO2. When this effect was incorporated, Kasting found that CO2 by itself is inadequate to warm the surface. SO2 absorbs strongly in the near UV region of the solar spectrum. While a small amount of SO2 may have a negligible effect by itself on the surface temperature, it may have significantly warmed the middle atmosphere of early Mars, much as ozone warms the terrestrial stratosphere today. If this region is kept warm enough to inhibit the condensation of CO2, then CO2 remains a viable greenhouse gas. Our preliminary radiative modeling shows that the addition of 0.1 ppmv of SO2 in a 2 bar CO2 atmosphere raises the temperature of the middle atmosphere by approximately 10 degrees, so that the upper atmosphere in a 1 D model remains above the condensation temperature of CO2. In addition, this amount of SO2 in the atmosphere provides an effective UV shield for a hypothetical biosphere on the martian surface.

NASA Discipline Exobiology↗
NASA NTRS2014

Improved Satellite Retrievals of NO2 and SO2 over the Canadian Oil Sands and Comparisons with Surface Measurements

Satellite remote sensing is increasingly being used to monitor air quality over localized sources such as the Canadian oil sands. Following an initial study, significantly low biases have been identified in current NO2 and SO2 retrieval products from the Ozone Monitoring Instrument (OMI) satellite sensor over this location resulting from a combination of its rapid development and small spatial scale. Air mass factors (AMFs) used to convert line-of-sight "slant" columns to vertical columns were re-calculated for this region based on updated and higher resolution input information including absorber profiles from a regional-scale (15 km × 15 km resolution) air quality model, higher spatial and temporal resolution surface reflectivity, and an improved treatment of snow. The overall impact of these new Environment Canada (EC) AMFs led to substantial increases in the peak NO2 and SO2 average vertical column density (VCD), occurring over an area of intensive surface mining, by factors of 2 and 1.4, respectively, relative to estimates made with previous AMFs. Comparisons are made with long-term averages of NO2 and SO2 (2005-2011) from in situ surface monitors by using the air quality model to map the OMI VCDs to surface concentrations. This new OMI-EC product is able to capture the spatial distribution of the in situ instruments (slopes of 0.65 to 1.0, correlation coefficients of greater than 0.9). The concentration absolute values from surface network observations were in reasonable agreement, with OMI-EC NO2 and SO2 biased low by roughly 30%. Several complications were addressed including correction for the interference effect in the surface NO2 instruments and smoothing and clear-sky biases in the OMI measurements. Overall these results highlight the importance of using input information that accounts for the spatial and temporal variability of the location of interest when performing retrievals.

surface concentration↗
NASA NTRS1973

SO2 Spectroscopy with A Tunable UV Laser

A portion of the fluorescence spectrum of SO2 has been studied using a narrow wavelength doubled dye laser as the exciting source. One purpose of this study is to evaluate the use of SO2 resonance re-emission as a probe of SO2 in the atmosphere. When the SO2 is excited by light at 300.2 nm, for example, a strong reemission peak is observed which is Stokes-shifted from the incident light wavelength by the usual Raman shift (the VI symmetric vibration frequency 1150.5/cm ). The intensity of this peak is sensitive to small changes (.01 nm) in the incident wavelength. Measurements of the N2 quenching and self quenching of this re-emission have been obtained. Preliminary analysis of this data indicates that the quenching is weak but not negligible. The dye laser in our system is pumped by a pulsed N2 laser. Tuning 'and spectral narrowing are accomplished using a telescope-echelle grating combination. In a high power configuration the resulting pulses have a spectral width of about 5 x 10(exp -3) nm and a time duration of about 6 nsec. The echelle grating is rotated by a digital stepping motor, such that each step shifts the wavelength by 6 x 10(exp -4) nm. In addition to the tunable, narrow wavelength uv source and spectral analysis of the consequent re-emission, the system also provides time resolution of the re-emitted light to 6 nsec resolution. This capability is being used to study the lifetime of low pressure S02 fluorescence at different wavelengths and pressures.

Morey, W. W.↗
NASA NTRS2016

Using CATS Near-Real-time Lidar Observations to Monitor and Constrain Volcanic Sulfur Dioxide (SO2) Forecasts

An eruption of Italian volcano Mount Etna on 3 December 2015 produced fast-moving sulfur dioxide (SO2) and sulfate aerosol clouds that traveled across Asia and the Pacific Ocean, reaching North America in just 5 days. The Ozone Profiler and Mapping Suite's Nadir Mapping UV spectrometer aboard the U.S. National Polar-orbiting Partnership satellite observed the horizontal transport of the SO2 cloud. Vertical profiles of the colocated volcanic sulfate aerosols were observed between 11.5 and 13.5 km by the new Cloud Aerosol Transport System (CATS) space-based lidar aboard the International Space Station. Backward trajectory analysis estimates the SO2 cloud altitude at 7-12 km. Eulerian model simulations of the SO2 cloud constrained by CATS measurements produced more accurate dispersion patterns compared to those initialized with the back trajectory height estimate. The near-real-time data processing capabilities of CATS are unique, and this work demonstrates the use of these observations to monitor and model volcanic clouds.

space↗
NASA NTRS2016

What is Eating Ozone? Thermal Reactions between SO2 And O3: Implications for Icy Environments

Laboratory studies are presented, showing for the first time that thermally driven reactions in solid H2O+SO2+O3 mixtures can occur below 150 K, with the main sulfur-containing product being bisulfate (HSO4(-)). Using a technique not previously applied to the low-temperature kinetics of either interstellar or solar system ice analogs, we estimate an activation energy of 32 kJ per mol for HSO4(-) formation. These results show that at the temperatures of the Jovian satellites, SO2 and O3 will efficiently react making detection of these molecules in the same vicinity unlikely. Our results also explain why O3 has not been detected on Callisto and why the SO2 concentration on Callisto appears to be highest on that world's leading hemisphere. Furthermore, our results predict that the SO2 concentration on Ganymede will be lowest in the trailing hemisphere, where the concentration of O3 is the highest. Our work suggests that thermal reactions in ices play a much more important role in surface and sub-surface chemistry than generally appreciated, possibly explaining the low abundance of sulfur-containing molecules and the lack of ozone observed in comets and interstellar ices.

Loeffler, Mark J.↗
NASA NTRS2018

High-resolution SOFIA/EXES Spectroscopy of SO2 Gas in the Massive Young Stellar Object MonR2 IRS3: Implications for the Sulfur Budget

Sulfur has been observed to be severely depleted in dense clouds leading to uncertainty in the molecules that contain it and the chemistry behind their evolution. Here, we aim to shed light on the sulfur chemistry in young stellar objects (YSOs) by using high-resolution infrared spectroscopy of absorption by the ν3 rovibrational band of SO2 obtained with the Echelon-Cross-Echelle Spectrograph on the Stratospheric Observatory for Infrared Astronomy. Using local thermodynamic equilibrium models we derive physical parameters for the SO2 gas in the massive YSO MonR2 IRS3. This yields a SO2/H abundance lower limit of 5.6 ± 0.5 × 10(exp -7), or >4% of the cosmic sulfur budget, and an intrinsic line width (Doppler parameter) of b < 3.20 km s(exp -1). The small line widths and high temperature (Tex = 234 ± 15 K) locate the gas in a relatively quiescent region near the YSO, presumably in the hot core where ices have evaporated. This sublimation unlocks a volatile sulfur reservoir (e.g., sulfur allotropes as detected abundantly in comet 67P/Churyumov–Gerasimenko), which is followed by SO2 formation by warm, dense gas-phase chemistry. The narrowness of the lines makes formation of SO2 from sulfur sputtered off grains in shocks less likely toward MonR2 IRS3.

Infrared ISM↗
DOE OSTI2020

Materials Data on Na3As(SO2)4 by Materials Project

Na3(SO2)4As crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional and consists of four arsenic molecules and one Na3(SO2)4 framework. In the Na3(SO2)4 framework, there are four inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a square co-planar geometry to four O2- atoms. There are two shorter (2.44 Å) and two longer (2.52 Å) Na–O bond lengths. In the second Na1+ site, Na1+ is bonded in a square co-planar geometry to four O2- atoms. There are two shorter (2.35 Å) and two longer (2.39 Å) Na–O bond lengths. In the third Na1+ site, Na1+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Na–O bond distances ranging from 2.26–2.48 Å. In the fourth Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.35–2.95 Å. There are four inequivalent S2+ sites. In the first S2+ site, S2+ is bonded in a water-like geometry to two O2- atoms. There is one shorter (1.51 Å) and one longer (1.67 Å) S–O bond length. In the second S2+ site, S2+ is bonded in a water-like geometry to two O2- atoms. There is one shorter (1.49 Å) and one longer (1.50 Å) S–O bond length. In the third S2+ site, S2+ is bonded in a single-bond geometry to one O2- atom. The S–O bond length is 1.55 Å. In the fourth S2+ site, S2+ is bonded in a water-like geometry to two O2- atoms. There is one shorter (1.50 Å) and one longer (1.51 Å) S–O bond length. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted T-shaped geometry to two Na1+ and one S2+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+ and one O2- atom. The O–O bond length is 1.46 Å. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two Na1+ and one S2+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Na1+ and one S2+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two equivalent Na1+ and one S2+ atom. In the sixth O2- site, O2- is bonded in a distorted linear geometry to one Na1+ and one S2+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to two Na1+ and one S2+ atom. In the eighth O2- site, O2- is bonded in a distorted single-bond geometry to one Na1+, one S2+, and one O2- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Materials Data on Na2P2H3(SO2)2 by Materials Project

(Na4P4H5(SO2)4)2H2 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of two hydrogen molecules and one Na4P4H5(SO2)4 sheet oriented in the (0, -1, 1) direction. In the Na4P4H5(SO2)4 sheet, there are four inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 4-coordinate geometry to two H+0.33+, one S2-, and one O2- atom. There are one shorter (2.48 Å) and one longer (2.55 Å) Na–H bond lengths. The Na–S bond length is 2.86 Å. The Na–O bond length is 2.39 Å. In the second Na1+ site, Na1+ is bonded in a 2-coordinate geometry to two H+0.33+, one S2-, and three O2- atoms. There are one shorter (2.53 Å) and one longer (2.66 Å) Na–H bond lengths. The Na–S bond length is 2.91 Å. There are a spread of Na–O bond distances ranging from 2.31–2.77 Å. In the third Na1+ site, Na1+ is bonded in a 3-coordinate geometry to two H+0.33+, one S2-, and two O2- atoms. There are one shorter (2.37 Å) and one longer (2.69 Å) Na–H bond lengths. The Na–S bond length is 2.93 Å. There are one shorter (2.32 Å) and one longer (2.38 Å) Na–O bond lengths. In the fourth Na1+ site, Na1+ is bonded in a 4-coordinate geometry to one S2- and three O2- atoms. The Na–S bond length is 2.94 Å. There are a spread of Na–O bond distances ranging from 2.22–2.41 Å. There are four inequivalent P+4.50+ sites. In the first P+4.50+ site, P+4.50+ is bonded to one S2- and three O2- atoms to form distorted corner-sharing PSO3 tetrahedra. The P–S bond length is 1.96 Å. There are a spread of P–O bond distances ranging from 1.51–1.65 Å. In the second P+4.50+ site, P+4.50+ is bonded to one S2- and three O2- atoms to form distorted corner-sharing PSO3 tetrahedra. The P–S bond length is 2.00 Å. There are a spread of P–O bond distances ranging from 1.49–1.64 Å. In the third P+4.50+ site, P+4.50+ is bonded to one S2- and three O2- atoms to form distorted corner-sharing PSO3 tetrahedra. The P–S bond length is 1.96 Å. There are a spread of P–O bond distances ranging from 1.51–1.65 Å. In the fourth P+4.50+ site, P+4.50+ is bonded to one S2- and three O2- atoms to form distorted corner-sharing PSO3 tetrahedra. The P–S bond length is 1.96 Å. There are a spread of P–O bond distances ranging from 1.52–1.64 Å. There are five inequivalent H+0.33+ sites. In the first H+0.33+ site, H+0.33+ is bonded in a single-bond geometry to one Na1+ atom. In the second H+0.33+ site, H+0.33+ is bonded in a single-bond geometry to one Na1+ atom. In the third H+0.33+ site, H+0.33+ is bonded in a distorted L-shaped geometry to two Na1+ atoms. In the fourth H+0.33+ site, H+0.33+ is bonded in a single-bond geometry to one Na1+ atom. In the fifth H+0.33+ site, H+0.33+ is bonded in a single-bond geometry to one Na1+ atom. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted L-shaped geometry to one Na1+ and one P+4.50+ atom. In the second S2- site, S2- is bonded in a 1-coordinate geometry to two Na1+ and one P+4.50+ atom. In the third S2- site, S2- is bonded in a 2-coordinate geometry to one Na1+ and one P+4.50+ atom. In the fourth S2- site, S2- is bonded in a single-bond geometry to one P+4.50+ atom. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Na1+ and two P+4.50+ atoms. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one Na1+ and one P+4.50+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+ and one P+4.50+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two P+4.50+ atoms. In the fifth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two P+4.50+ atoms. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+ and one P+4.50+ atom. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to two Na1+ and one P+4.50+ atom. In the eighth O2- site, O2- is bonded in a bent 120 degrees geometry to two P+4.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na3Au(SO2)4 by Materials Project

Na3(SO2)4Au crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional and consists of four gold molecules and one Na3(SO2)4 framework. In the Na3(SO2)4 framework, there are three inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.40–2.84 Å. In the second Na1+ site, Na1+ is bonded in a distorted octahedral geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.33–2.72 Å. In the third Na1+ site, Na1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Na–O bond distances ranging from 2.29–2.99 Å. There are four inequivalent S2+ sites. In the first S2+ site, S2+ is bonded in a single-bond geometry to one O2- atom. The S–O bond length is 1.54 Å. In the second S2+ site, S2+ is bonded in a single-bond geometry to one O2- atom. The S–O bond length is 1.54 Å. In the third S2+ site, S2+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There is one shorter (1.47 Å) and two longer (1.48 Å) S–O bond length. In the fourth S2+ site, S2+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There is one shorter (1.46 Å) and two longer (1.49 Å) S–O bond length. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to four Na1+ and one S2+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two Na1+ and one S2+ atom. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Na1+ and one S2+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+ and one S2+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two Na1+ and one S2+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Na1+ and one S2+ atom. In the seventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Na1+ and one S2+ atom. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Na1+ and one S2+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS2015

A Decade of Change in NO2 and SO2 over the Canadian Oil Sands As Seen from Space

A decade (20052014) of observations from the Ozone Monitoring Instrument (OMI) were used to examine trends in nitrogen dioxide(NO2) and sulfur dioxide (SO2) over a large region of western Canada and the northern United States, with a focus on the Canadian oil sands. In the oil sands, primarily over an area of intensive surface mining, NO2 tropospheric vertical column densities (VCDs) are seen to be increasing by as much as 10year, with the location of the largest trends in a newly developing NO2 lobe well removed from surface monitoring stations. SO2 VCDs in the oil sands have remained approximately constant. The only other significant increase in the region was seen in NO2 over Bakken gas fields in North Dakota which showed increases of up to5yr. By contrast, other locations in the region show substantial declines in both pollutants, providing strong evidence to the efficacy of environmental pollution control measures implemented by both nations. The OMI-derived trends were found to be consistent with those from the Canadian surface monitoring network, although in the case of SO2, it was necessary to apply a correction in order to remove the residual signal from volcanic eruptions present in the OMI data.

NO2↗
NASA NTRS1972

Calculation of pressure-broadened linewidths of SO2 and NO2.

The Anderson-Tsao-Curnutte theory of line broadening (1949, 1962) is applied to calculate the self-broadened and N2- and O2-broadened linewidths of SO2 and NO2. Computed linewidth values are in good agreement with available experimental results and with calculations by Murphy and Boggs (1967, 1969) on four self-broadened and one nitrogen-broadened lines. Air-broadened linewidths are also calculated for SO2 at 200, 250 and 300 K. The results are considered to be useful for predicting theoretical spectra of SO2 under atmospheric conditions.

Tejwani, G. D. T.↗
NASA NTRS1979

Boundary layer measurements of the OH radical in the vicinity of an isolated power plant plume - SO2 and NO2 chemical conversion times

Direct measurements of the OH radical in the vicinity of an isolated power plant plume are reported. These measurements were used to estimate the conversion time of SO2 to H2SO4-sulfate aerosol via the initiating step OH + SO2 + M yields HSO3. Using the near-high-noon measured value of OH (9.5 million per cu cm), resulted in a 1/e conversion time of 1.4 days. The latter lifetime would correspond to a conversion rate of about 2%/hr. When the lifetime calculation was modified to take into consideration the OH diurnal cycle, the 1/e conversion time for SO2 was found to be 4.4 days, giving an apparent overall rate of conversion of about 0.7%/hr. Similar calculations carried out for the conversion of NO2 to NHO3 resulted in 1/e lifetimes for NO2 of 2-3 h for midday time periods.

Davis, D. D.↗
NASA NTRS1980

A model of the SO2 atmosphere and ionosphere of Io

The calculations of thermal structure for an SO2 atmosphere of Io lead to exospheric temperatures in 800-1200 K range. The Pioneer 10 electron density profiles can be fit with an SO2 surface density of 1.2 x 10 to the 11th per cu cm at 5:30 pm local time and exosphere temperature of 1030 K. Low energy electrons provide the major ionization source but the solar UV absorption dominates the heating of the atmosphere due to the long wavelength absorption threshold of SO2 and large absorption cross sections.

Kumar, S.↗
NASA NTRS1980

The enhanced oxidation of SO2 by NO2 on carbon particulates

The oxidation of SO2 on carbon particles in dry air and in air at 65% relative humidity (RH) was found to be greatly enhanced by the presence of gaseous NO2. Exposures of 20-80ppm SO2 + 10ppm NO2 on 1-mg samples of commercial carbon black were found to produce both sorption and desorption coverages (weight retained after desorption into N2) of over one order of magnitude greater than for corresponding SO2 exposures. Significant agglomeration and wetting were observed to occur progressively during exposures at 65% RH, and samples, even after 150-h exposure, rarely reached steady-state weight gain. The wetting may have regenerated fresh reactive carbon surface. Sorptions conducted in nitrogen atmospheres, rather than in air, appeared to produce slightly higher sorptions and weight retentions for equivalent exposure concentrations and times, indicating that NO2 served as the oxidizer and that molecular oxygen, or some trace constitutents in air, may have weakly inhibited the oxidation by NO2. Wet chemical analysis of the desorbed phase indicated that sulfate, presumably H2SO4 accounted for over half of the retained weight. Measurements of pH from water-quenched samples indicated a highly acidic surface phase, and suggested the oxidation process could proceed in an acidic environment.

Cofer, W. R., III↗