Sulphuric Acid Aerosol Research Articles

16 O 02 Formation of polar stratospheric clouds: Nucleation and freezing mechanisms of nitric acid and sulphuric acid aerosols

16 O 02 Formation of polar stratospheric clouds: Nucleation and freezing mechanisms of nitric acid and sulphuric acid aerosols

Increased chlorine dioxide over Antarctica caused by volcanic aerosols from Mount Pinatubo

THE annual springtime depletion of Antarctic ozone1 has been shown to be due to the action of chlorine species, activated by reactions occurring on the surfaces of polar stratospheric clouds (PSCs)1,2. Similar reactions may also take place on the surfaces of liquid sulphuric acid aerosols when the temperature is too high to permit the formation of PSCs3–4. Such processes may have been facilitated following the eruption of Mount Pinatubo in June 1991, when unprecedented amounts of sulphur compounds were injected into the stratosphere5. Here we present observations of Antarctic chlorine dioxide abundances in the austral autumn and winter of 1991 (when aerosol concentrations were at background levels) and 1992 (greatly enhanced aerosol concentrations). We find that in 1992, unlike 1991, chlorine dioxide levels increased dramatically in the autumn, when PSCs were extremely unlikely to have been present. Model results suggest that this was mainly caused by the direct activation of chlorine nitrate on the aerosol surfaces. The effect of the Pinatubo aerosols probably contributed to the unprecedented depth and areal extent of Antarctic ozone depletion in 1992.

Surface ozone depletion in Arctic spring sustained by bromine reactions on aerosols

NEAR-TOTAL depletion of the ozone in surface air is often observed in the Arctic spring, coincident with high atmospheric concentrations of inorganic bromine1–5. Barrie et al.1 suggested that the ozone depletion was due to a catalytic cycle involving the radicals Br and BrO (ref. 6); however, these species are rapidly converted to the nonradical species HBr, HOBr and BrNO3, quenching ozone loss. McConnell et al.7 proposed that cycling of inorganic bromine between aerosols and the gas phase could maintain sufficiently high levels of Br and BrO to destroy ozone, but they did not specify a mechanism for aerosol-phase production of active bromine species. Here we propose such a mechanism, based on known aqueous-phase chemistry, which rapidly converts HBr, HOBr and BrNO3 back to Br and BrO radicals. This mechanism should be particularly efficient in the presence of the high concentrations of sulphuric acid aerosols observed during ozone depletion events3.

Reactions on sulphuric acid aerosol and on polar stratospheric clouds in the Antarctic stratosphere

Heterogeneous chemistry producing active chlorine has been identified as crucial to Antarctic ozone depletion. Most attention has focussed on reactions on solid polar stratospheric cloud (PSC) particles, although there is still no satisfactory understanding of the microchemical incorporation of HCl in PSCs. The alternative mechanism involving sulphuric acid aerosol as the reaction surface has been considered at lower latitudes, but its role in the special conditions of the polar stratosphere has been largely ignored. Recent data from the Antarctic stratosphere have suggested that HCl is present in sulphuric acid aerosol that remains liquid even at the lowest stratospheric temperatures. The available laboratory data show that cold, relatively dilute, sulphuric acid is particularly able to take up HCl that is available for reaction provided the aerosol remains liquid. Fast heterogeneous reaction rates compared to those at mid‐latitudes will produce active chlorine rapidly. Since the aerosol is present with significant surface area throughout the lower stratosphere, it should be very effective for heterogeneous reaction once temperatures drop. These surfaces, rather than PSCs, could host the initial conversion of Cl to its active form over the Antarctic.

Dimensions and dynamics of co-ignimbrite eruption columns

VERY powerful volcanic eruptions cannot always form classical Plinian eruption columns1–4. Instead, collapsing fountains may develop above the vent and shed pyroclastic flows which spread laterally along the ground5. The upper part of these hot, dense pyroclastic flows may become buoyant through the entrainment, heating and expansion of ambient air, coupled with the sedimentation of larger clasts suspended in the flow. The buoyant material may rise, in a co-ignimbrite eruption column, carrying massive quantities of fine dust and volatiles into the stratosphere6,7. Here we present a model of this process, and show that the co-ignimbrite columns associated with the eruptions of Toba8,9 75,000 years ago and Tambora10 in 1815 may have ascended only about 32 and 23 km; the latter is comparable with the less powerful 1982 Plinian eruption column of El Chichon11. This corroborates arguments that the mass of sulphuric acid aerosols injected into the stratosphere and not the eruptive power determines the climatic impact of an eruption12,13.

Sulphuric acid aerosol formation by irradiation: particlesize distribution and model calculations

Particle formation by an adjustable irradiation source has been studied. Air that containssulphur dioxide and water vapour has been irradiatied in a flow reactor. In the aerosol measurements both CNC (TSI 3025) and EMS (DMA, VIE-08) have been used. Significant particle formation has been detected to occur already on doses in the order of 0.1 mGy. Particle number concentration is dependent on absorbed dose, also particle size is proportional to the dose. An attempt to interprete the results quantitatively has been carried out.

Future changes in stratospheric ozone and the role of heterogeneous chemistry

HETEROGENEOUS chemical reactions on the surfaces of solid or liquid particles present in the lower stratosphere may be an important influence on the levels of ozone depletion resulting from increased concentrations of anthropogenic chlorine compounds in the atmosphere1. Such processes, occurring on ice particles in polar stratospheric clouds, have been invoked to explain the formation of the springtime ozone hole over Antarctica2,3. Sulphuric acid aerosols injected into the atmosphere following a volcanic eruption may also provide sites for heterogeneous chemistry leading to ozone depletion4. Here we present model calculations that assess the importance of heterogeneous processes in future ozone depletion, assuming that trace-gas concentrations follow the protocol agreed at the recent international convention in London. We find that, even if this protocol is adhered to, reactions on the surface of sulphuric acid aerosol particles could produce significant ozone depletion into the beginning of the next century, especially if a major volcanic eruption (similar to the El Chichon eruption of 19824) takes place.

Evidence for stratospheric ozone-depleting heterogeneous chemistry on volcanic aerosols from El Chichón

STRATOSPHERIC aerosols are thought to promote ozone destruction by reactive halogen compounds in the polar stratosphere. The predominant aerosol usually comprises particles of nitric acid trihydrate; surface-catalysed reactions on these particles produce ozone-destroying halogen compounds and remove reactive nitrogen gases which might otherwise render the halogen compounds inactive1,2. For periods of up to two years after major volcanic eruptions, atmospheric concentrations of sulphuric acid aerosols in the stratospheric eruption cloud may be comparable to those of nitric acid aerosols, and might therefore also play a part in atmospheric heterogeneous chemistry. Indeed, ozone levels in the Northern Hemisphere were observed to decrease following the large eruption of the Mexican volcano El Chichon in 19823,4. Here we report balloon-borne measurements of trace gases made in June 1982 in the stratospheric eruption cloud of El Chichon. We observe an increase in the concentration of nitric acid, which is probably due to the conversion of reactive nitrogen gases on sulphate aerosols. These reactions are therefore likely to have played a part in the destruction of stratospheric ozone.

Depletion of H2O2 in a Greenland ice core: implications for oxidation of volcanic SO2

MAJOR volcanic eruptions inject large quantities of sulphur compounds into the atmosphere1. A principal component is sulphur dioxide; subsequent oxidation of SO2 in the atmosphere to sulphuric acid aerosol may lead to climate perturbations2. Here we present evidence to suggest that SO2 oxidation may occur at high latitudes by reaction with H2O2. Variations in sulphate and H2O2 concentrations in four sections of a Greenland ice core (corresponding to four volcanic events) show that high sulphate concentrations, from volcanic fallout, are accompanied by depletion of H2O2. This suggests that some of the volcanic sulphur was still in the form of SO2 when it reached Greenland, and was then oxidized by H2O2 in Greenland precipitation. As SO2 oxidation in the stratosphere is very slow, volcanic events that inject SO2 into the stratosphere could produce large depletions of distant H2O2 reservoirs when the material is later reinjected into the troposphere.

Sulphuric acid aerosol formation by irradiation: A flow reactor set up

We present a flow reactor set up which has been designed and built for experiments on irradiation induced aerosol particle formation. The effect of various parameters on the dynamics of aerosol formation can be studied. The main feature of the device is the possibility to control the sulphuric acid production rate by varying the intensity of irradiation field.

Effects of Inhaled Oxidant and Acidic Air Pollutant Combinations on Nasal and Tracheal Tissues in Exercising Rats

Author(s): Kleinman, MT; Mc Clure, TR; Mautz, WJ; Phalen, RF; Crocker, TT | Abstract: Groups of rats inhaled mixtures of O3 and acid particles for three hours while exercising. One group received purified air, a second group breathed 0.6 ppm O3, a third group breathed a mixture: SO2 (5 ppm) plus sulphuric acid aerosol containing iron and manganese ions (1 mg/m3, 0.5 µm mass median aerodynamic diameter). The fourth and fifth groups breathed the above mixture plus 0.6 ppm O3; group 4 was exposed while exercising and group 5 was exposed at rest. Tritiated thymidine (3HT) was injected into the rats 17 hours post-exposure; lungs, trachea, and nasal airways were fixed and sectioned. Focal lesion areas were measured in the parenchyma and3HT uptake by replicating cells in the upper airways was determined by autoradiography. Significant amounts of label were incorporated by squamous and respiratory epithelia of the nose, but little uptake was observed in the olfactory or tracheal tissue. In the squamous tissue none of the exposures resulted in labelling rates in excess of those observed in rats exposed to purified air. In respiratory epithelium, however, the acid-containing multicomponent atmospheres significantly increased labelling rates above background in animals exposed while exercising. O3 alone did not affect3HT uptake, nor did the presence or absence of 03 in the multicomponent atmosphere alter the observed uptake rates. © 1988 The British Occupational Hygiene Society.

Comparison of Responses and Deposition Following Human Exposures Via Oral or Nasal Inhalation of Sulphuric Acid Aerosols

Controlled human exposure studies with inhaled air pollutants frequently utilize mouth breathing. To determine the extent that the route of inhalation influences airway resonses to particulate pollutants, we examined pulmonary responses of asthmatics breathing sulfuric acid (H₂SO₄)aerosols by oral or nasal inhalation. Asthmatics were exposed to H₂SO₄aerosols in a 45m³chamber for one hour including 10minutes of exercise or via a mouthpiece for 16 minutes during resting ventilation. We produced aerosols in concentrations of 100 μg/m³and 450 μg/m³. We measured before and immediately after all exposures FYC, FEV, and specific airway conductance (SGaw). At the 450 μg/m³ concentration, there were remarkable similarities in airway resonses desite the different exosure routes . Although the exposures were not strictly comarable in duration. we calculated tracheobronchial (TB) deposition for the two modes of aerosol administration and utilized con temorary models for deposition in explaining the lack of qualitative and quantitative distinctions in the pattern of response.

Direct identification of sulphuric acid aerosol from the oxidation of SO 2 by ozone in the presence of hydrocarbon traces

Direct identification of sulphuric acid aerosol from the oxidation of SO 2 by ozone in the presence of hydrocarbon traces

Acid rain: Effects on arachidonic acid metabolism in perfused and ventilated guinea-pig lung

Isolated, perfused and ventilated guinea-pig lungs were exposed for 10 min to acid (sulphuric + nitric acid) aerosol mimicking acid rain at pH 4.5 or 2.5, as well as to a control distilled water aerosol (pH 6.0–6.5). Lung perfusing solution was recovered and thromboxane (TX) B 2 and leukotriene (LT) B 4 were measured by radioimmunoassay (RIA) techniques. In a series of experiments TXB 2 release averaged 0.43 ± 0.18 (± SD) ng/min during exposure to distilled water aerosol and increased to 0.70 ± 0.30 ng/min during exposure to acid aerosol at pH 4.5 ( P < 0.05). In a second series of experiments TXB 2 release was 0.46 ± 0.18 ng/min and increased to 1.07 ± 0.51 ng/min ( P < 0.01) after acid aerosol at pH 2.5. In both cases LTB 4 release, reflecting lipoxygenase activity, was unchanged. LTC 4 levels were not measurable under basal conditions as well as after exposure to acid aerosol. A pneumoconstriction was also observed, being more pronounced after acid aerosol at pH 2.5. Individual sulphuric and nitric acid aerosol component solutions at pH 2.5 evoked TXB 2 and airway resistance changes corresponding to those observed with the mixed acid aerosol. LTB 4 was not modified. Acid rain inhalation may directly stimulate pathways leading to the bronchoconstrictor and pro-aggregating TXA 2 synthesis in isolated guinea-pig lung, without affecting the lipoxygenase pathway of arachidonic acid metabolism.

Effects of long-term natural acidification on the algal communities of tundra ponds at the Smoking Hills, N.W.T., Canada

Epipelic and planktonic algal communities have been examined periodically for 3 years from four tundra ponds which have very low pH values (1.8–3.6) and high heavy metal concentrations due to long-term fumigation by sulphur dioxide and sulphuric acid aerosols from nearby lignite burns. These communities have been compared with those of control ponds which are situated further from the burns and have alkaline waters (pH 8) due to calcareous marl soils. The 90 species identified from the control ponds are members of nine classes of algae. In contrast, 14 species have been observed in the fumigated ponds which are representatives of four classes, the Chlorophyceae, Euglenophyceae, Bacillariophyceae, and Cryptophyceae. The plankton of the control ponds is typical of tundra ponds in that it is dominated by small flagellates, particularly the cryptomonad Chroomonas minuta. Diatoms such as Amphora, Navicula and Surirella species, are the major components of the epipelic periphyton of these ponds, accounting for 67 to 90% of the biomass. Most of the primary productivity and biomass of the algae in the acidified ponds is benthic (3.7 versus 0.17 mg C m−2 h−1 for epipelon and plankton, respectively). The dominant species in the fumigated ponds include Chlamydomonas acidophila, Euglena mutabilis, Nitzschia communis, Eunotia arcus, and Eunotia glacialis. Fine structural examination of Euglena and Nitzschia indicates that these species are healthy under conditions of pH 1.8 and high heavy metals. These results show that the flora of the fumigated ponds is atypical of tundra ponds but rather is similar to that of very acidic temperate waters such as those draining coal-mined areas or volcanic lakes.

Barium oxalate as a selective solid reagent for the absorption of sulphur trioxide

Barium and calcium oxalate monohydrates have been shown to be more suitable absorbents for sulphur trioxide than either anhydrous or hydrated oxalic acid. All four compounds are selective absorbents for the trioxide and do not absorb sulphur dioxide. Similarly all are elective absorbents for sulphuric acid aerosol, although the calcium salt may be decarboxylated under these conditions. Lead oxalate and formate may be suitable for the absorption of SO 3 and H 2S, and SO 3, H 2S and SO 2 respectively.

Photochemical oxidation of atmospheric sulphur dioxide

Oxidation of atmospheric sulphur dioxide can occur by homogeneous photochemically initiated gas-phase reactions as well as by heterogeneous reactions in cloud and fog droplets. Gas phase oxidation can result from reactions of excited SO 2 molecules formed by absorption of solar u.v. radiation by ground state SO 2 , from reactions of SO 2 with photochemically generated OH and RO 2 free radicals, and from its reaction with transient species produced in thermal ozone—alkene reactions. Evaluation of the available mechanistic and rate data reveals that, of these three processes, oxidation by free radicals, particularly OH, is likely to be the most important in the atmosphere. Oxidation rates of up to 4 % h -1 are predicted for a hydrocarbon-NO x polluted atmosphere under western European summertime conditions. This can lead to the formation of elevated concentrations of sulphuric acid and sulphate aerosol in polluted air. In the natural background troposphere oxidation rates are much less, ca . 0.3 % h -1 averaged over 24 h, but probably still significant as a source of atmospheric sulphates.

Sulphate Emissions from Automobile Exhaust

The installation of platinum group metal catalysts on 1975 model year U.S. automobiles for control of CO/HC emissions has led to concern over the tendency of such catalysts to oxidise SO2 to sulphuric acid aerosol. Examination of sulphate emissions from Johnson Matthey and Volkswagen test vehicles suggests that although there is some tendency to form sulphate, especially under highly oxidising conditions, the levels of sulphate are in general low. Comparison of measured sulphate conversion with thermodynamic equilibrium values shows that only a small fraction of the available exhaust SO2 is converted to sulphate, and that the catalyst’s ability to convert is shortlived. Future moves toward a three-way catalyst capable of simultaneously converting CO/HC and NOx pollutants should eradicate any tendency towards sulphuric acid formation in automobile exhaust.

The growth of sulphuric acid aerosol particles when contacted with water vapour

When aerosols of 100% sulphuric acid were contacted with humidified nitrogen it was observed that droplet-vapour equilibrium was reached in less than a few seconds. Calculations of diffusion rates to and into sub-micron sized droplets have predicted this equilibration to be complete in 10 −510 −2 s, depending on original size and surface accommodation. It is inferred that a dropletvapour chemical interaction such as occurs in the atmosphere will be controlled by reaction kinetics, and will be independent of droplet size in the sub-micron range. The dependences of liquid-phase conversion rate on volume fraction and on concentration of a dissolved reactant are in some common circumstances mutually cancelling. It can be concluded that in the event of acid droplets being inhaled there is no risk of their reaching lung tissue before substantial dilution has occurred.

A simple photometric determination of sulphuric acid aerosol

Sulphuric acid aerosol in air may be determined after collection on a filter as equivalent to the amount diaethylamine it absorbs from a stream of dry air to which this reactant has been added in vapour form. This amount may be determined by a simple photometric method. The detection limit is about 0.2 μg m −3, the reproducibility is about 10 per cent. Other acidic particles interfere to an extent in the order of 20 per cent, depending on acid strength and physical state.