Selective Reduction of Nitrogen Oxides In Combustion Flue Gases

The body of Information presented in this paper is directed to those Individuals concerned with the removal of NO_x in combustion flue gases. A catalytic process for the selective reduction of nitrogen oxides by ammonia has been investigated. Efforts were made toward the development of catalysts resistant to SO_x poisoning. Nitrogen oxides were reduced over various metal oxide catalysts in the presence or absence of SO_x(SO₂ and SO₃). Catalysts consisting of oxides of base metals (for example, Fe₂O₃) were easily poisoned by SO₃, forming sulfates of the base metals. A series of catalysts which are not susceptible to the SO_x poisoning has been developed. The catalysts possess a high activity and selectivity over a wide range of temperatures, 250—450°C. The catalysts were tested in a pilot plant which treated a flue gas containing 110-150 ppm NO_x, 660-750 ppm SO₂, and 40-90 ppm SO₃. The pilot plant was operated at 350°C and at a space velocity of 10,000 h^-1. The removal of nitrogen oxides was more than 90% for several months.

A mechanism of the NO-NH₃ reaction has also been investigated. It is found that NO reacts with NH₃ at a 1:1 mole ratio in the presence of oxygen and the reaction is completely inhibited by the absence of oxygen. The experimental data show that the NO-NH₃ reaction in the presence of oxygen is represented byNO + NH₃ + 1/4 O₂ = N₂ + 3/2 H₂O.     

Dynamic NO adsorption characteristics of iron-treated activated carbon fibers

The breakthrough curve for NO adsorption on the activated carbon fibers treated in iron salt solutions was determined. They can adsorb much more NO than granular activated carbon by a factor of more than 10 from a flowing 300 ppm NO-N₂ mixed gas at 100°C and 20 ml min⁻¹; the most effective one of the iron-treated carbon fibers of 0.2 g is able to reduce the NO concentration from 300 ppm to 30 ppm. These adsorbents can adsorb the same amount of NO from even a 300 ppm NO-500 ppm SO₂-10% CO₂-10% H₂O-1% O₂-N₂ mixed gas.     

Salinity increases mobility of heavy metals in soils

The effect of salinity induced by CaCl₂, MgCl₂, NaCl and Na₂SO₄ on the mobility of Cu, Cd, Pb and Zn was studied. An increase of ionic strength by any salts promoted a higher release of Cd than the others metals. When CaCl₂ and NaCl were applied, Cd and Pb showed the highest degree of mobilization. When MgCl₂ was applied, Cd and Cu were mobilized the most. Finally, an increase of Na₂SO₄ also promoted the strongest mobilization of Cd and Cu.As the total heavy metal content was higher, the percentage of Pb and Cu released upon salinization decreased, indicating that these metals are strongly bound to soil constituents. An increase of carbonates in the soil promoted a higher release of Pb for all used salts and for Zn when MgCl₂ and NaCl were used. This indicates that Pb and Zn are adsorbed on the surface of carbonate crystals. An increase of fine particles promoted a decrease of percentage of released Cd for all salts, indicating that Cd is strongly retained in the fine fractions.The main mechanism regulating Pb and Cd mobility was competition with Ca²⁺ for sorption sites followed for metal chloro-complexation, association between the Cd/Pb-sulfates and competition with Mg²⁺. The main mechanism regulating Cu mobility was the formation of Cu-sulfate, followed by competition with cations (Mg > Ca) and chloride. For Zn, competition with Ca²⁺ for sorption sites was the most important process for its mobility; followed by Zn-sulfate association and, finally, chloride and competition with Mg with the same effect.     

Stainless Steel Anti-Smog Mufflers—Cut Air Pollution

An automatic process gas chromatograph has been developed for use on the recovery furnace stack of a Kraft pulp mill. The instrument analyzes for widely varying concentrations of H₂S, SO₂, CH₃SH and higher order sulfur compounds. It is insensitive to the fixed gases and water vapor, and performs its analysis in approximately ten minutes. The instrument features a microcoulometric detector giving it sensitivity to H₂S as low as 0.1 ppm, and SO₂ and CH₃SH as low as 0.5 ppm. The major limit to even higher sensitivity at this stage of development lies with two problems: the background noise level in the detector and the sulfur compound absorption in the Porapak Q chromatograph column. At the reported sensitivity, a 40-ml gas sample was used. The instrument also contains a data analysis system supplementary to the usual strip chart recorder. This system is made up of a digital voltmeter, a digital translator, and a teletype and hence allows the transfer of the output data to a digital computer for processing. The processed data are usually presented in the form of ppm quantities of the component gases in the stack gas. The instrument has worked successfully on small furnace effluent for periods of 25 hr but has not been tried on recovery furnace stacks. It has also run on prepared samples for periods of up to seven days with no maintenance or attendance necessary.     

Dissociation of Sulfur Hexafluoride Tracer Gas in the Presence of an Indoor Combustion Source

ABSTRACT

As an odorless, nontoxic, and inert compound, sulfur hexafluoride (SF₆) is one of the most widely used tracer gases in indoor air quality studies in both controlled and uncontrolled environments. This compound may be subject to reactions with water vapor under elevated temperature to form acidic inorganic compounds such as HF and H₂SO₄. Thus, in the presence of unvented combustion sources such as kerosene heaters, natural gas heaters, gas log fireplaces, candles, and lamps, the SF₆ dissociation may interfere with measurements of the emissions from these sources. Tests were conducted in a research house with a vent-free natural gas heater to investigate these potential interferences. It was observed that the heater operation caused about a 5% reduction of SF₆ concentration, which can be an error source for the ventilation rate measurement and consequently the estimated pollutant emission rates. Further analysis indicates that this error can be much greater than the observed 5% under certain test conditions because it is a function of the ventilation flow rate. Reducing the tracer gas concentration has no effect on this error. A simple theoretical model is proposed to estimate the magnitude of this error.

The second type of interference comes from the primary and secondary products of the SF₆ dissociation, mainly H₂SO₄, SO₂, HF, and fine particulate matter (PM). In the presence of ~5 ppm SF₆, the total airborne concentrations of these species increased by a factor of 4-10. The tests were performed at relatively high SF₆ concentrations, which is necessary to determine the interferences quantitatively. The second type of interference can be significantly reduced if the SF₆ concentration is kept at a low ppb level.     

A Study of Sulfur Dioxide in Photochemical Smog I. Effect of SO2 and Water Vapor Concentration in the 1-Butene/NOx/SO2 System

There is an appreciable chemical interaction between SO₂ and photochemical smog which depends on the concentration of SO₂ and water vapor. The rate of decay of SO₂ concentration is greatly increased in the presence of photochemical smog. With 0.75 ppm SO₂, a light-scattering aerosol is produced in dry systems and systems at 22 and 55% relative humidity (RH). Aerosol is not observed until after the NO₂ peak has been reached and the NO concentration has fallen to a very low value. The formation of aerosol corresponds in time to the region of most rapid decrease in the SO₂ profile. In systems at 65% RH or with smaller amounts of SO₂, no light scattering is observed, but the percentage of SO₂ disappearing is greater. In relatively dry systems the presence of SO₂ results in a general slowing down of the photochemical smog reactions. In systems containing water vapor concentrations comparable to those found in the atmosphere, the inhibiting influence of SO₂ on the smog reaction is less pronounced. However, the maximum concentration of oxidant produced by the photochemical smog reactions is significantly lower when SO₂ is present.     

Chain Scission of Polymers by Small Concentrations (1 to 5 ppm) of Sulfur Dioxide and Nitrogen Dioxide,Respectively, in Presence of Air and Near Ultraviolet Radiation

Results are presented as to the extent of chain scission (crosslinking) suffered by various polymers exposed to 1 atm of air and near ultraviolet light (λ > 2800 Å) in presence and absence of nitrogen dioxide, sulfur dioxide, and ozone, respectively, in the concentration range of 1 to 5 ppm. Vinyl polymers are scarcely affected by SO₂ and NO₂, respectively; however, nylon and elastomers are quite sensitive toward these gases. These conclusions agree with observations, found in the literature, on tensile tests, elongations, flexibilities, and infrared measurements in presence of sulfur dioxide under similar conditions.     

The Contribution of Sulfate and Nitrate to Atmospheric Fine Particles During Winter Inversion Fogs in Cache Valley,Utah

Abstract

Air pollutants were collected in Logan, Cache County, UT, in February 1993 during two periods of atmospheric inversion accompanied by fog. The following atmospheric species were determined: (1) gaseous SO₂, NO₂ (semi-quantitatively),HNO3, NH3, and HF; (2) fine particulate SO₄ ⁼, NO₃ ^-, NH₄ ⁺, F–, H⁺, C, Si, S, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Pb, Se, Br, and Sr, and; (3) fine particulate mass, which was calculated. The major components of fine particulate matter were carbonaceous material, ammonium nitrate, and ammonium sulfate, while the soil component was small. Calculated, fine particulate mass averaged 80 μg/m³ and reached concentrations as high as 120 μg/m³. SO₂/So_x and NO₂/NO_y mole ratios generally varied between 0.2 and 0.1 during inversions. These ratios also showed moderate but consistent diurnal patterns. The emission inventory for Cache County indicates sources of SO₂ and NO_x but not significant amounts of primary sulfate and nitrate. The observations reported here indicate there is significant conversion of SO₂ and NO_x in the presence of excess oxidants to sulfuric and nitric acid that are neutralized by excess ammonia.     

Intercomparison of two techniques for the preparation of gaseous sulfur calibration standards in the low to sub-ppb range

Calibration gas standards for H₂S, CH₃SH, CS₂ and SO₂, independently prepared by two separate research groups from the University of Idaho Department of Chemistry and the NOAA Aeronomy Laboratory, were directly intercompared using a gas chromatographic-flame photometric measurement procedure for all four species and a fluorimetric measurement procedure for H₂S. The NOAA gas standard system used gravimetrically-calibrated ‘low loss’ permeation tubes in conjunction with a three-stage dynamic dilution system. The University of Idaho (UI) system used single-stage dilution of the effluent from ‘ultra-low loss’ permeation tubes, which were calibrated by a metal foil collection/flash desorption/flame photometric detection procedure using aqueous sulfate standards. Comparative measurements between UI and NOAA gas standards in the 1–2 ppbv range showed differences no greater than 12 % for CS₂, SO₂ and CH₃SH, and 21 % for H₂S.     

Biochemical and Physiological Detection of Sulfur Dioxide Injury to Pea Plants (Pisum sativum)

Biochemical and physiological experiments were conducted on pea plants (Pisum sativum) continuously exposed in growth chambers to SO₂ gas for 18 days. S0₂ gas concentrations were 0.1, 0.15, and 0.25 ppm. In plants exposed to 0.1 and 0.15 ppm it was clearly demonstrated that there was a greater accumulation of inorganic sulfur, a reduced buffer capacity of the cells relative to H-ions, and a stimulation of glutamate dehydrogenase activity. The only macroscopic symptom seen was slight chlorosis of the older leaves. There was only a slight decrease in fresh and dry weights of these plants compared to the control plants whereas in the group of plants exposed to 0.25 ppm SO₂ foliage necrosis was considerable. In addition, there was a marked reduction in the fresh and dry weights of the latter plants. However, the relationship among accumulated inorganic sulfur, reduced buffer capacity, and increased glutamate dehydrogenase activity as seen for the lower S0₂ concentrations was close. Accordingly, if might be possible to use these three parameters to diagnose S0₂ injury before any significant symptoms appear. In the case of severe SO₂ injury there was a marked increase in glutamine and ammonia concentrations suggesting that these factors in addition to the above could be used in diagnosing severe SO₂ injury. There was no significant difference between plants treated with 0.1 or 0.15 ppm SO₂ and control plants in the contents of K, Ca, P, and N fractions. Therefore, these factors would not be useful in the early detection of SO₂ injury.     

The air pollution caused by the burning of fireworks during the lantern festival in Beijing

The effects of the burning of fireworks on air quality in Beijing was firstly assessed from the ambient concentrations of various air pollutants (SO₂, NO₂, PM_2.5, PM₁₀ and chemical components in the particles) during the lantern festival in 2006. Eighteen ions, 20 elements, and black carbon were measured in PM_2.5 and PM₁₀, and the levels of organic carbon could be well estimated from the concentrations of dicarboxylic acids. Primary components of Ba, K, Sr, Cl⁻, Pb, Mg and secondary components of C₅H₆O₄²⁻, C₃H₂O₄²⁻, C₂O₄²⁻, C₄H₄O₄²⁻, SO₄²⁻, NO₃⁻ were over five times higher in the lantern days than in the normal days. The firework particles were acidic and of inorganic matter mostly with less amounts of secondary components. Primary aerosols from the burning of fireworks were mainly in the fine mode, while secondary formation of acidic anions mainly took place on the coarse particles. Nitrate was mainly formed through homogeneous gas-phase reactions of NO₂, while sulfate was largely from heterogeneous catalytic transformations of SO₂. Fe could catalyze the formation of nitrate through the reaction of α-Fe₂O₃ with HNO₃, while in the formation of sulfate, Fe is not only the catalyst, but also the oxidant. A simple method using the concentration of potassium and a modified method using the ratio of Mg/Al have been developed to quantify the source contribution of fireworks. It was found that over 90% of the total mineral aerosol and 98% of Pb, 43% of total carbon, 28% of Zn, 8% of NO₃⁻, and 3% of SO₄²⁻ in PM_2.5 were from the emissions of fireworks on the lantern night.     

Characteristics of re-suspended road dust and its impact on the atmospheric environment in Beijing

A sampling campaign of re-suspended road dust samples from 53 sites that could cover basically the entire Beijing, soil samples from the source regions of dust storm in August 2003, and aerosol samples from three representative sites in Beijing from December 2001 to September 2003, was carried out to investigate the characteristics of re-suspended road dust and its impact on the atmospheric environment. Ca, S, Cu, Zn, Ni, Pb, and Cd were far higher than its crustal abundances and Ca²⁺, SO₄²⁻, Cl⁻, K⁺, Na⁺, NO₃⁻ were major ions in re-suspended road dust. Al, Ti, Sc, Co, and Mg in re-suspended road dust were mainly originated from crustal source, while Cu, Zn, Ni, and Pb were mainly derived from traffic emissions and coal burning, and Fe, Mn, and Cd were mainly from industrial emissions, coal combustion and oil burning. Ca²⁺ and SO₄²⁻ mainly came from construction activities, construction materials and secondary gas-particle conversions, Cl⁻ and Na⁺ were derived from industrial wastewater disposal and chemical industrial emissions, and NO₃⁻ and K⁺ were from vehicle emissions, photochemical reactions of NO_X, biomass and vegetable burning. The contribution of mineral aerosol from inside Beijing to the total mineral aerosols was ∼30% in spring of 2002, ∼70% in summer of 2002, ∼80% in autumn of 2003, ∼20% in PM₁₀ and ∼50% in PM_2.5, in winter of 2002. The pollution levels of the major pollution species, Ca, S, Cu, Zn, Ni, Pb, Fe, Mn, and Cd in re-suspended road dust reached ∼76%, ∼87%, ∼75%, ∼80%, ∼82%, ∼90%, ∼45%, ∼51%, and ∼94%, respectively. Re-suspended road dust from the traffic and construction activities was one of the major sources of pollution aerosols in Beijing.     

Effects of Sulfur Dioxide and Nitric Oxide on Mercury Oxidation and Reduction under Homogeneous Conditions

Abstract

This paper is particularly related to elemental mercury (Hg⁰) oxidation and divalent mercury (Hg²⁺) reduction under simulated flue gas conditions in the presence of nitric oxide (NO) and sulfur dioxide (SO₂). As a powerful oxidant and chlorinating reagent, Cl₂ has the potential for Hg oxidation. However, the detailed mechanism for the interactions, especially among chlorine (Cl)-containing species, SO₂, NO, as well as H₂O, remains ambiguous. Research described in this paper therefore focused on the impacts of SO₂ and NO on Hg⁰ oxidation and Hg²⁺ reduction with the intent of unraveling unrecognized interactions among Cl species, SO₂, and NO most importantly in the presence of H₂O. The experimental results demonstrated that SO₂ and NO had pronounced inhibitory effects on Hg⁰ oxidation at high temperatures when H₂O was also present in the gas blend. Such a demonstration was further confirmed by the reduction of Hg²⁺ back into its elemental form. Data revealed that SO₂ and NO were capable of promoting homogeneous reduction of Hg²⁺ to Hg⁰ with H₂O being present. However, the above inhibition or promotion disappeared under homogeneous conditions when H₂O was removed from the gas blend.     

Photo-Oxidation of Sulfur Dioxide

SO₂/O₂ mixtures were photolyzed at 3130 Å and in the range 2500–4000 Å at room temperature. The only product of photolysis was SO₃. Attempts to estimate ф(S0₃) using mass spectrometry, l.R. spectroscopy and pressure change measurements were unsuccessful, because it was not possible to obtain reproducible quantitative estimates of SO₃. ф(SO₂) values were determined by monitoring the 3130 Å absorption for its concentration measurements. ф(SO₂) was independent of SO₂ (11.6 to 50.4 torr) and O₂ (50.0 to 390.6 torr) pressures. At 3130 Å, ф(SO₂) varied between 1.5 × 10^?2 and 2.2 X 10^?2. Over the integrated range 2500–4000 Å ф(SO₂) values of 2.1 X 10^?3 to 2.9 X 10^?3 were obtained. The differences in ф(SO₂) values are explained in terms of wavelength dependence of the rate constants for the two primary reactions: ¹SO₂ + SO₂ → 2SO₂(1) and ¹SO₂ + SO₂ → ³SO₂ + SO₂(2); (k₂/k₁) _{3130 Å} ≈ 10(k₂/k₁)_{2500–4000 Å}.     

Sensitivity of Native Desert Vegetation To SO2 and to SO2 and NO2 Combined

Interest in air pollution injury to native vegetation has been generated with the construction and planned construction of large coal-fired power plants near the coal reserves in the southwest desert areas of the United States. Since information on the effects of SO₂ on these native species was not available in the literature, fumigation studies were conducted with portable chambers placed over native species in the field with SO₂ and SO₂ + NO₂. Pollutant concentrations were measured and controlled with instruments located in a mobile laboratory. Each fumigation was of two hours duration and the concentration ranged from 0.5 to 11 ppm SO₂ and from 0.1 to 5 ppm NO₂. Concentrations of SO₂ above 2 ppm were required to cause injury to all but a few of the 87 species studied. Many of the native desert species proved to be highly resistant to injury from these gases.     

Lidar measurements of sulfur dioxide and ozone in the boundary layer during the 1983 Fos Berre Campaign

Studies of the dispersion of pollutants (SO₂, O₃) in the planetary boundary layer have been performed during the Fos Berre 1983 International Campaign using ground-based DIAL lidar operating in the u.v. wavelength range. Multidimensional measurements of both SO₂ and O₃ were obtained with a spatial resolution better than 500 m, a temporal resolution of 3 mn and a maximum horizontal range of 3 km. The overall accuracy as assessed by various comparisons with other measurement systems was always better than 20%. Examples of application to studies of SO₂ dispersion in the planetary boundary layer, of plume evolution and of horizontal inhomogeneities in the ozone field are given.     

Simultaneous sampling of NH3, HNO3, HC1, SO2 and H2O2 in ambient air by a wet annular denuder system

A new sampling device is described for the simultaneous collection of NH₃, HNO₃, HCl, SO₂ and H₂O₂ in ambient air. The apparatus is based on air sampling by two parallel annular denuder tubes. The gases are collected by absorption in solutions present in the annulus of the denuder tubes. After a sampling time of 30 min at flow rate of 32 ℓ min⁻¹ the solutions are extracted from the denuders and analyzed off-line. The detection limits of NH₃, HNO₃, HCL and SO₂ are in the order of 0.1–0.5 μm⁻³. For H₂O₂ the detection limit is 0.01 μm⁻³. The reproducibility is 5–10% at the level of ambient air concentrations. Comparison of this novel technique with existing methods gives satisfactory results. The compact set-up offers the possibility of field experiments without the need of extensive equipment.     

Effects of SO2 and/or NO2 on Native Plants of the Mojave Desert and Eastern Mojave-Colorado Desert

Ten species of plants, five perennials and five annuals, native to the Mojave desert were grown in pots and fumigated in open top plastic greenhouses, 25 hours/week, with SO₂ and/or NO₂. Three levels of SO₂: 2.0, 0.67, and 0.22 parts per million (ppm); three levels of NO₂: 1.0, 0.33, and 0.11 ppm; three treatments with 2.0 ppm SO₂ + 1.0 ppm NO₂, 0.67 ppm SO₂ + 0.33 ppm NO₂ and 0.22 ppm SO₂ + 0.11 ppm NO₂ plus untreated control plants were used in the fumigations. The perennials were fumigated for 16 weeks in 1977 and 32 weeks in 1978. Three species of annuals were grown and fumigated for 17 weeks, a fourth for 16 weeks, and a fifth for 12 weeks. A second crop of the first three annuals were grown; one for 12 weeks, a second for 8, and a third for 9 weeks.

Individual species differed widely in their particular responses to the fumigants. The fumigations of perennials with 2.0 ppm of SO₂ or NO₂ at 1.0 ppm caused extensive leaf injury, and reduced growth or dry weight of Larrea divaricate Cav., Chilopsls linearis Cav., and Ambrosia dumosa (Gray) Payne. The combined fumigants had additive effects. No suggestion of synergism was noted. These fumigants at lower concentrations stimulated lateral growth of Encelia farinosa Gray ex Torr. and Erodium cicutarium (L.) L’Her., dry weight of Atriplex canescens (Pursh) Nutt. and Plantago insularis Eastw. and increased flowering of Balleya pleniradiata Harv. and Gray, thus indicating beneficial effects.

Annual species were more severely affected by 2.0 ppm SO₂ than the perennials and extensive injury or death of plants occurred in all annuals. At the 0.67 ppm level severe leaf injury occurred. NO₂ at 1.0 ppm was less injurious than SO₂ and addition of NO₂ to SO₂ suggested an antagonistic effect. Plant survival and flowering was increased by adding NO₂ to plants being treated with SO₂

Comparison of perennial species showed Larrea sensitive, Chilopsis, Encella and Ambrosia intermediate, and Atriplex resistant. The annual species showed Erodium cicutarium and Plantago Insularis to be extremely sensitive, Phacelia crenulata Torr very sensitive and Baileya pleniradiata sensitive. Chaenactis carphoclinia Gray grew poorly and no valid rating was possible.     

Humidity effects on photochemical aerosol formation in the SO2-NO-C3H6-air system

In order to investigate the effects of humidity on the gas-phase oxidation of SO₂ in polluted air and on the subsequent aerosol formation process, photoirradiation experiments were carried out by means of a 4-m³ chamber, in which mixtures containing SO₂, NO and C₃H₆ with concentrations in the ppm range were exposed to simulated solar radiation in different relative humidity (r.h.) conditions. The total amount of oxidized SO₂ was quantified from the SO₄²⁻ yield determined by the chemical analysis of the aerosol product, and a part due to the oxidation by the OH radical was evaluated by estimating the OH concentration from the decay rate of C₃H₆. The remaining part was assigned to the oxidation by the Criegee intermediate, as it had a good correlation with the progress of the O₃ + C₃H₆ reaction. The contributions of the two oxidizing species to the total conversion and the oxidation rate of SO₂ were measured as functions of r.h. As a result, experimental evidence was obtained for the prediction of Calvert and Stockwell's (1983, Envir. Sci. Technol. 17, 428A–443A) simulation that the oxidation due to the Criegee intermediate was retarded by the increase in humidity. The OH contribution, on the other hand, was almost independent of r.h. It was observed consequently that the total oxidized amount of SO₂ considerably decreased as r.h. was higher.The humidity effect on the aerosol formation process was found to be more complicated than the effect on the gas-phase chemistry. The maximum rate of increase in the particle number concentration rose linearly with increasing r.h., but the number concentration itself measured at its maximum or at the end of the irradiation reached a ceiling value around r.h. = 30% and went down for higher r.h. The average panicle size in the final stage of the reaction showed a minimum around the same r.h. at which the number concentration was maximum. The H₂SO₄ concentration in the mist particles, however, decreased monotonically as r.h. got higher. It was suggested that these different responses against the increase in humidity resulted from the cooperation of several processes such as the H₂SO₄ monomer formation, the H₂O condensation, the particle coagulation, etc., which had different dependences on r.h.     

Interactions of Sulfur Dioxide with Insoluble Suspended Particulate Matter

A laboratory study was conducted of the heterogeneous catalysis of sulfur dioxide at ppm concentrations in air by insoluble particles of CaCO₂, V₂O₅, Fe₂0₃, flyash from a coal-burning power plant, MnCO₂, activated carbon, and suspended particulate matter from urban air. The investigalion was performed by utilizing a new technique for aerosol stabilization which consists of depositing the aerosol on Teflon beads in a fluidized bed. The Teflon beads with deposited aerosol particles were then packed into a flow reactor. Progress of the chemical reaction of SO₂ with deposited particles was continuously monitored by determining the SO₂ concentrations in the reactor effluent with a microcoulometer.

In this investigation, CaCOg, V₂O₅, and flyash were essentially inert to SO₂ at room temperature. Fe₂O₃, activated carbon, MnO₂, and suspended particulate matter from urban air sorbed SO₂ from air streams with up to 14.4 ppm SO₂ in air. Evidence is presented which suggests that a substantial part of the sorbed SO₂ was physically adsorbed.

Bioassay procedures which utilize pulmonary flow resistance changes in guinea pigs to monitor response to inhaled SO₂-aerosol mixtures in air have indicated the weak or non-potentiating capacity of insoluble aerosols as contrasted to soluble aerosols. Potentiating response of an aerosol appears to be strongly associated with reaction of SO₂ in a water droplet containing aerosol ions and not with physically adsorbed SO₂ on an insoluble aerosol.