AIR DECONTAMINATION DEVICE & METHOD

Abstract

A device for air decontamination comprises a housing (10) having an air inlet (14), an air outlet (16) and an air flow passage (12) therebetween, the housing including at least one non-thermal plasma cell (22); wherein the non-thermal plasma cell is sized and positioned relative to the internal dimensions of the housing such that a portion of air entering the housing from the air inlet is adapted to pass through and across the non-thermal plasma cell and a portion of air entering the housing from the air inlet is adapted to pass outside of the external surface of the non-thermal plasma cell. A method of decontaminating air is also disclosed.

Claims

1. A device for air decontamination comprising a housing having an air inlet, an air outlet and an air flow passage therebetween, the housing including at least one non-thermal plasma cell located downstream of the air inlet; wherein the non-thermal plasma cell is sized and positioned relative to the internal dimensions of the housing such that a portion of air entering the housing from the air inlet is adapted to pass through and across the non-thermal plasma cell and a portion of air entering the housing from the air inlet is adapted to pass outside of the external surface of the non-thermal plasma cell.

2. A device for air decontamination as claimed in claim 1, further comprising at least one UV radiation emitting device and/or at least one ozone catalysing device which are located within the housing, coincident with, partly coincident with or downstream of the non-thermal plasma cell.

3. A device for air decontamination as claimed in claim 1, wherein the air flow passage in the housing of the air decontamination device comprises a first air passage and a second air passage, the first air passage being adapted to carry the portion of air which passes through and across the non-thermal plasma cell and the second air passage being adapted to carry the portion of air which passes outside of the external surface of the non-thermal plasma cell.

4. A device for air decontamination as claimed in claim 3, wherein the first air passage and the second air passage are permeable to permit air to move therebetween.

5. A device for air decontamination as claimed in claim 3, wherein the UV radiation emitting device is positioned within the first air passage of the housing.

6. A device for air decontamination as claimed in claim 3, wherein the ozone catalysing device is positioned such that air in the first air passage is adapted to pass through the ozone catalysing device and air in the second air passage is adapted to pass over the external surface of the ozone catalysing device.

7. A device for air decontamination as claimed in claim 3, wherein the external surface of the first air passage is defined by the external surface of the non-thermal plasma cell and the external surface of the ozone catalysing device.

8. A device for air decontamination as claimed in claim 3, wherein the housing is elongate and the first and second air passages extend in the direction of the length of the housing, with the first air passage being surrounded by the second air passage.

9. A device for air decontamination as claimed in claim 1, further comprising a device for delivering hydrocarbons in the vicinity of the air outlet of the housing of the air decontamination device, said hydrocarbon delivery device having an air inlet, an air outlet and an air flow passage therebetween.

10. A device for air decontamination as claimed in claim 9, wherein the hydrocarbon delivery device comprises a reservoir of one or more hydrocarbons located in the air flow passage of the hydrocarbon delivery device, such that incoming air is adapted to pick up the hydrocarbons as it flows through the air flow passage, and wherein the hydrocarbons in the air are delivered within the housing of the air decontamination device in the vicinity of the air outlet of the housing.

11. (canceled)

12. (canceled)

13. A device for air decontamination as claimed in claim 1, wherein the housing further comprises a shield extending in the direction of the air flow passage, the internal surface of the shield being spaced from and facing the non-thermal plasma cell, such that a portion of air entering the housing from the air inlet is adapted to pass outside of the external surface of the shield, this portion of air being separate from the portion of air which is adapted to pass through and across the non-thermal plasma cell and being separate from the portion of air which is adapted to pass outside of the external surface of the non-thermal plasma cell.

14. A device for air decontamination as claimed in claim 13, wherein the housing further comprises a third air passage which is adapted to carry the portion of air which passes outside of the external surface of the shield.

15. A device for air decontamination as claimed in claim 14, wherein the shield is adapted to shield air flowing in the third air passage from electromagnetic emissions from the non-thermal plasma cell.

16. A device for air decontamination as claimed in claim 14, wherein the housing is elongate and the first, second and third air passages extend in the direction of the length of the housing, with the first air passage being surrounded by the second air passage and with the second air passage being surrounded by the third air passage.

17. A device for air decontamination as claimed in claim 1, further comprising an air stream generator located at the air inlet of the housing, upstream of the non-thermal plasma cell.

18. A device for air decontamination as claimed in claim 1, further comprising an air turbulence creating device located within the housing at or towards the air outlet of the housing, downstream of the non-thermal plasma cell.

19. A device for air decontamination as claimed in claim 18, wherein the air turbulence creating device is shaped and positioned to terminate at least a portion of the air flow passage of the housing with at least one curved or linear surface adjacent the air outlet of the housing, the surface being adapted to mix, and optionally re-direct, air passing through the device.

20. A method of decontaminating air comprising the steps of: a) directing an air stream to be decontaminated through and across a non-thermal plasma cell so that free radicals are produced by which contaminants in the air stream are oxidised; b) directing an air stream to be decontaminated externally of the non-thermal plasma cell so that free radicals are produced by which contaminants in the air stream are oxidised; c) controlling ozone in the air streams output from the non-thermal plasma cell; and d) introducing a hydrocarbon with two or more carbon-carbon double bonds into the air stream to react with residual ozone to control the air quality so that the air stream is suitable for human exposure.

21. A method of decontaminating air as claimed in claim 20, wherein the method further comprises directing an air stream, which has not been decontaminated by the effects of a non-thermal plasma cell, to mix with and dilute the air streams decontaminated by the effects of the non-thermal plasma cell.

22. A method of decontaminating air as claimed in claim 20 using the device claimed in claim 1.

Description

[0081] The present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:

[0082] FIG. 1 shows a diagrammatic cross-sectional side view of an air decontamination device, in accordance with a first embodiment of the invention;

[0083] FIG. 2 shows perozone chemistry;

[0084] FIG. 3 shows a diagrammatic cross-sectional side view of an air decontamination device, in accordance with a second embodiment of the invention;

[0085] FIG. 4 shows a cross-sectional view along line X-X of FIG. 3;

[0086] FIG. 5 shows a diagrammatic cross-sectional side view of an air decontamination device, in accordance with a third embodiment of the invention; and

[0087] FIG. 6 shows a perspective view of part of the air decontamination device according to the third embodiment of the invention.

[0088] Referring to FIG. 1, there is shown an air decontamination device which comprises a housing 10 having a flow passage 12, an air inlet 14 to the flow passage 12 and an air outlet 16 exiting from the flow passage 12, and a compartment 18 adjacent to the flow passage 12. An air stream generator 20, a non-thermal plasma cell 22, an ultraviolet (UV) radiation emitting device 24, an ozone catalysing device 26, and a hydrocarbon emitter 28 are located in the passage 12. The emitter forms part of a hydrocarbon delivery device 52. The flow passage 12 has a first (inner) passage 12a and a second (outer) passage 12b.

[0089] The air stream generator 20 is provided adjacent the air inlet 14 of the passage 12. The air stream generator 20, in this embodiment, is an electric fan 30 powered by mains electricity or battery packs (not shown) provided in the compartment 18 of the housing 10. As a safety measure, a grill 32 is provided across the air inlet 14 to prevent accidental access to the fan 30 while in operation.

[0090] The non-thermal plasma cell 22 is positioned adjacent the fan 30, downstream of the air inlet 14. In one embodiment the plasma cell 22 comprises an annular ceramic dielectric ring having a series of circular holes or longitudinal slots around its circumference. Sheets of metal electrodes, forming a cathode 34 and an anode 36, are wrapped around its circumference. Thus, preferably, the dielectric is a perforated ring of ceramic material, with porous annular electrodes internally and externally fitted, about the circumference. The cathode 34 and anode 36 are powered by an adjustable power supply unit (PSU) 40 housed in the compartment 18 of the housing 10.

[0091] The cathode 34 and anode 36 comprise reticulated (three dimensionally porous) conductive elements, in this case being ceramic and stainless steel composites. However, any rigid reticulated conductive or semi-conductive material could be used.

[0092] The dielectric 38 may be ceramic. However, again, the dielectric 38 could be any suitable material to suit varying applications and specific requirements. The dielectric 38 material may be coated with a catalytic material.

[0093] The UV radiation emitting device 24 includes an ultraviolet light emitting device powered by a PSU 44 (power supply unit) housed in the compartment 18 of the housing 10. The UV light emitting device is disposed in the passage 12, downstream of the non-thermal plasma filter 22, and coincident with the ozone catalysing device 26. The UV light emitting device may comprise one or more UV tubes or UV LEDs.

[0094] The ozone catalysing device 26 comprises a mesh 46 disposed across the passage 12 and surrounding the UV radiation emitting device 24. The mesh 46 includes a coating of ozone catalysing material, such as a mixture of titanium, lead and manganese oxides.

[0095] The hydrocarbon delivery device 52 comprises a hydrocarbon emitter 28 which is supplied from a rechargeable hydrocarbon reservoir 48 located in an evaporator chamber 50 for evaporating liquid hydrocarbon held in the reservoir 48. The liquid hydrocarbon is preferably contained within a membrane. The hydrocarbon delivery device has an air inlet 54, an air outlet 56 and an air flow passage 58 therebetween. The air flow passage is located, at least in part, outside of the housing of the air decontamination device. The hydrocarbon reservoir and the evaporator chamber are disposed along the air flow passage so that air passing through the air flow passage picks up discharged gaseous hydrocarbon and delivers it to the hydrocarbon emitter 28. The air stream generator (fan 30) assists in driving the hydrocarbon-containing air through the hydrocarbon delivery device.

[0096] In this embodiment, the air flow passage of the hydrocarbon delivery device is only in fluid communication with the air flow passage of the air decontamination device at the air inlet and air outlet of the hydrocarbon delivery device. This has the advantage that air entering the air flow passage 58 from the air inlet 54 is substantially free of ozone produced by the plasma cell, meaning that the hydrocarbon picked up by the flowing air is not immediately oxidized by ozone and other by-products. Hence, when released by the hydrocarbon emitter, the hydrocarbon is effective in reacting with and controlling residual ozone in the air stream about to exit the air decontamination device.

[0097] The air inlet of the hydrocarbon delivery device is preferably adapted to draw air from the vicinity of the air inlet of the housing of the air decontamination device. The air flow produced by the air stream generator creates a pressure differential between the air inlet (which has a positive pressure) and the air outlet (which has a negative pressure) of the hydrocarbon delivery device. This pressure differential acts to drive the hydrocarbon through the hydrocarbon delivery device, resulting in a sufficiently constant delivery of the hydrocarbon through the hydrocarbon emitter.

[0098] The hydrocarbon reservoir 48 contains a liquid hydrocarbon, for example an olefin such as a terpene and, more specifically, myrcene or linalool.

[0099] The outlet of the hydrocarbon emitter 28 is located at or in the vicinity of the centre of the passage 12 of the housing 10, and downstream of the UV light emitting device and mesh 46 of the ozone catalysing device 26. The outlet of the hydrocarbon emitter 28 is therefore located adjacent the outlet 16 of the passage 12 of the housing 10.

[0100] Preferably, the rate of hydrocarbon emission is matched to the output of ozone produced by the air decontamination device, such that, in an equilibrium state, minimal surplus ozone (5-45 ppb) is reacted with minimal hydrocarbon to achieve a hydroxyl radical measurement of not less than 10.sup.6/cc.

[0101] Any other suitable means for supplying volatilised hydrocarbon to the outlet of the hydrocarbon emitter 28 can be used, provided that the hydrocarbon source is provided with an air supply not affected by the plasma cell or UV catalysis.

[0102] For example, the hydrocarbon delivery device may alternatively be an aerosol or other pressurised container fitted near the air outlet of the air decontamination device.

[0103] In this respect, the hydrocarbon, such as a terpene (for example, linalool), may be blended with an agent such as a surfactant or a chemical with properties which will render the terpene miscible with water, but will not react with the terpene, and has no properties which compromise the performance or safety of the device. There are many suitable surfactants commercially available which conform to these requirements. The hydrocarbon is then mixed with water which is preferably degassed and de-ionised.

[0104] The resulting hydrocarbon in an aqueous medium will enable the use of pressurised dispensers such as aerosol containers. Such pressurised dispensers may have outlets designed to work with the electronic controls of the air decontamination device for accurate dosing with very small amounts of terpene diluted in water. The very small amounts of terpene required for effectiveness, typically <50 mg/day, are difficult to control with a simple evaporative technique, such as used in the earlier devices. The dispensing container may be pressurised with an inert gas which will prevent degradation of the terpene, as will the degassing of the de-ionised water.

[0105] The hydrocarbon mixture may be sprayed from a suitably configured spray-head or other system consistent with highly accurate dosing to produce micro-droplets of water typically less than 0.5 microns.

[0106] De-ionised water is used to avoid reaction with the terpene or corrosion of the storage and delivery system, but has the advantage of humidifying the emissions from the device which will enhance hydroxyl radical output.

[0107] This is achieved because the terpene and surfactant mixture slightly reduces the surface tension of the water droplets in the spray. This has the effect of increasing the solubility of gaseous ozone in the water droplets. The ozone is naturally only sparingly soluble in water. When ozone gas surrounds a water micro-droplet, molecules of ozone move through the surface tension of the droplet which acts as a membrane, to react with either water molecules or terpene. With water, the ozone will produce peroxone, H.sub.2O.sub.3, which is highly reactive and then hydrogen peroxide; the reaction of ozone with the terpenes produces hydroxyl and hydroperoxyl radicals which in turn react with the hydrogen peroxide to produce more hydroxyl radicals. The water molecules released with this reaction also provide a source of hydrogen and oxygen atoms for further production of hydroxyl and hydroperoxyl radicals.

[0108] FIG. 2 illustrates peroxone chemistry, including the formation of H.sub.2O.sub.3 and ring-(HO.sub.2)(HO.sub.3) from O.sub.3.

[0109] Using a pressurised container, such as an aerosol, can simplify the hydrocarbon delivery process for certain applications but is not universally appropriate, particularly where devices remain isolated for extended periods.

[0110] At the air outlet 16 of the housing there is optionally provided a second fan 60 or another means of creating air turbulence, such as an obstruction (eg a non-motorised rotary blade). This is to provide better mixing of the air which has passed through the housing of the air decontamination device and the air which is delivering the hydrocarbon, resulting in decontaminated air with acceptable levels of ozone and formaldehyde (for example).

[0111] The air decontamination device can be solely powered by mains electricity, solely powered by battery packs, which may be rechargeable, or may be selectively energisable by both power sources.

[0112] The air decontamination device can be produced in the form of a portable device. Alternatively, the air decontamination device can be produced as a larger device intended to remain in one location once installed. The latter device is more suitable for, but not limited to, industrial or commercial installations and premises.

[0113] In use, the air decontamination device is positioned in the location to be decontaminated. The device is intended to decontaminate air within a building, chamber, enclosure, trunking, pipe, channel or other enclosed or substantially enclosed area. The device should be regulated to suit the chamber size being treated, so that the ozone level at equilibrium should never rise above pre-set levels under any circumstances due to failure of other components.

[0114] The device is preferably designed to emit not less than 10.sup.6 hydroxyl radicals per cc air.

[0115] In use, the device is energised, and the fan 30 generates a stream of ambient air along the first passage 12a and the second passage 12b of the housing 10. The air stream in the first passage passes initially through the non-thermal plasma cell 22. The air stream in the second passage passes initially outside of the external surface of the non-thermal plasma cell 22.

[0116] The plasma cell utilises the characteristics of a non-thermal plasma to plasmalise the constituent parts of the air. In general terms, the outer ring electrons in the atomic structure of the elements comprising air (principally oxygen and nitrogen) are excited by the intense electronic field generated by the non-thermal plasma, typically being 10 Kv at 20-30 KHz. The energised electrons release energy through collisions. However, little or no heat is emitted due to the insubstantial mass of the electrons and the consequent lack of ionisation that occurs. The release energy is sufficient to generate radicals within the air stream, such as O. and OH.. The radicals are powerful oxidants, and will oxidise hydrocarbons, organic gases, and particles typically 2.5 m and below, such as bacteria, viruses, spores, yeast moulds and odours and carbon particles. Only the most inert elements or compounds will generally resist oxidation.

[0117] Since many of the resultants of the oxidative reactions are transient and surface acting, due to having zero vapour pressure, by providing a molecular thick catalytic coating on some or all of the dielectric material of the non-thermal plasma, oxidation of particular molecules or compounds, for example nerve gas agents, within the non-thermal plasma can be targeted.

[0118] The non-thermal plasma cell 22 produces ozone as one of the by-products. This is entrained in the air stream leaving the non-thermal plasma cell 22. The half-life of ozone is dependent on atmospheric conditions and, itself being a powerful oxidant, under normal circumstances will continue to react in the air long after it has exited the plasma core. The initial control of excess ozone is carried out by the specification of the plasma cell power supply 40, by regulating the input of volts/current and by regulating the input of air by controlling the air stream generator 20.

[0119] The airstream leaving the non-thermal plasma cell 22 in the first passage passes over the UV radiation emitting device 24 within the surrounding ozone catalysing device 26. The airstream leaving the vicinity of the non-thermal plasma cell 22 in the second passage passes over the external surface of the ozone catalysing device 26. Although not shown in the diagrammatic drawing of FIG. 1, the ozone catalysing device is preferably close to or in contact with the non-thermal plasma cell to assist with the formation of the first and second passages; in this respect, a bridging piece (such as the ring-shaped piece shown in FIG. 6) may be positioned between the ozone catalysing device and the non-thermal plasma cell to assist with the formation of the first and second passages. The first passage and the second passage are permeable so that flowing air can permeate between them, meaning that the airstream in the second passage is also subject to the effects of the UV radiation emitting device and the ozone catalysing device.

[0120] Ultraviolet radiation emitted at 253.4-378 nanometres wavelength by the UV light emitting device acts to break down some of the ozone entrained in the air stream. The coating on the mesh 46 acts to catalyse this break down.

[0121] The destruction (photo-oxidation) of the ozone increases the radical level, particularly the level of hydroxyl radicals OH., within the air stream. These radials also vigorously oxidise contaminants remaining within the air stream.

[0122] The secondary fan 60 provides energy and turbulence to the treated air prior to it reaching the hydrocarbon emitter 28. This is to ensure good mixing of the air.

[0123] Trials have shown that hydroxyl and other radicals resident in the air stream after plasmalising significantly increase the rate of generation of free radicals during the photo-oxidative process.

[0124] It is not desirable to destroy all of the ozone entrained in the air stream from the plasma cell 22 using the UV radiation emitting device 24 and the ozone catalysing device 26.

[0125] The air stream in the first passage and the second passage exits the area of the ozone catalysing device 26, is mixed by the secondary fan 60 and passes along the passage 12 to the hydrocarbon emitter 28. The hydrocarbon emitter 28 discharges volatilised hydrocarbon into the air stream in order to control the remaining residual ozone to achieve desirable levels. Myrcene is suggested, since it is naturally occurring, has no known toxicity, and is widely used to extend perfumes and fragrances. However, linalool is preferred.

[0126] Linalool contains two carbon-carbon double bonds in its molecular structure:

##STR00001##

[0127] Ozone reacts preferentially with linalool evaporated into the air stream. When linalool reacts with ozone, a free radical cascade is triggered. More than thirty interrelated reactions occur, many of which produce a series of short half-life oxidants such as hydro peroxides, super oxides, hydroxy peroxides, and hydroxyl peroxides. Each of these oxidants breaks down, releasing yet further free radicals, which in turn promulgate the production of these oxidative species. This process continues in the chamber/area being treated until an equilibrium is reached between the emission and destruction of ozone by its reaction with the carbon-carbon double bonds of the hydrocarbon.

[0128] The products of these preferential reactions have zero vapour pressure, and hence condense on any remaining particle in the air stream or surface. As a result, decontamination of contaminants within the ambient air occurs, once the decontaminated air stream exits through the outlet 16 of the housing 10.

[0129] Due to the air decontamination device effectively recirculating and re-decontaminating air within an environment (eg the chamber/area), small particulates are removed as a result of the use of the non-thermal plasma cell 22, such that the device has an air filtering effect.

[0130] The air stream generator can be driven in reverse, enabling decontamination of the interior of the device by drawing excess free radicals entrained in the air stream back through the device. As such, the device is largely self-cleaning.

[0131] Referring to FIGS. 3 and 4, in a second embodiment of the invention, an air decontamination device comprises a housing 10 having a flow passage 12, an air inlet 14 to the flow passage 12 and an air outlet exiting from the flow passage 12. The device also has a compartment and a hydrocarbon delivery device in accordance with the first embodiment but these are not shown in FIG. 3 or 4. An air stream generator (eg fan 30), a non-thermal plasma cell 22, an ultraviolet (UV) radiation emitting device 24, an ozone catalysing device 26, and a hydrocarbon emitter 28 are located in the passage 12. The flow passage 12 has a first (inner) passage 12a and a second (outer) passage 12b.

[0132] Unless stated otherwise, the second embodiment of the device operates in the same way as the first embodiment of the device.

[0133] In this second embodiment, the UV radiation emitting device includes an ultraviolet light emitting tube which is disposed at least in part within the central region of an annular ring of the non-thermal plasma cell. The plasma field within this annular ring may be used to excite mercury provided in a mercury vapour tube to emit the UV radiation, in addition to decontamination of the air. This means that a separate power source for the UV radiation emitting device is not required.

[0134] Referring to FIG. 5, in a third embodiment of the invention, an air decontamination device comprises a housing 10 having a flow passage 12, an air inlet 14 to the flow passage 12 and an air outlet 16 exiting from the flow passage 12.

[0135] Unless stated otherwise, the third embodiment of the device operates in the same way as the first embodiment of the device. Although the ultraviolet (UV) radiation emitting device of the third embodiment is not positioned within the non-thermal plasma cell, it is possible for the ultraviolet (UV) radiation emitting device of the third embodiment to be positioned within the non-thermal plasma cell, in accordance with the second embodiment.

[0136] An air stream generator (eg fan 30), a non-thermal plasma cell 22, an ultraviolet (UV) radiation emitting device 24, an ozone catalysing device 26, and a hydrocarbon delivery device are located in the flow passage 12. The flow passage 12 has a first (inner) passage 12a, a second (middle) passage 12b and a third (outer) passage 12c.

[0137] The air stream generator is preferably larger in diameter than in the first embodiment to enable air to flow into all three passages. The air stream generator is spaced from the non-thermal plasma cell in the longitudinal direction of the housing.

[0138] A shield 62 is provided between the second (middle) passage 12b and the third (outer) passage 12c.

[0139] The shield 62 extends in the direction of the flow passage, the shield being positioned between, and spaced from, the non-thermal plasma cell 22 and the wall or walls of the housing 10.

[0140] As a result, a portion of air entering the housing from the air inlet 14 is adapted to pass outside of the external surface of the shield via third passage 12c, this portion of air being separate from the portion of air which is adapted to pass through and across the non-thermal plasma cell via first passage 12a, and being separate from the portion of air which is adapted to pass outside of the external surface of the non-thermal plasma cell via second passage 12b.

[0141] The different portions of air flowing towards the exit of the housing at the air outlet 16, are adapted to be mixed together at or adjacent to the air outlet to provide a dilution effect: in this respect, the untreated air from the third passage dilutes the treated (decontaminated) air from the first and second passages.

[0142] In this embodiment, the internal surface of the third passage 12c is defined by the external surface of the shield 62, and the external surface of the third passage is defined by the internal surface of the housing 10. Also, the internal surface of the second 12b passage is defined by the external surface of the non-thermal plasma cell 22 and the external surface of the ozone catalysing device 26, and the external surface of the second passage 12b is defined by the internal surface of the shield 62.

[0143] The housing is elongate and the first, second and third passages extend in the direction of the length of the housing, with the first passage 12a being surrounded by the second passage 12b and with the second passage being surrounded by the third passage 12c.

[0144] The shield is impermeable to air to prevent air moving from either the first passage 12a or the second passage 12b into the third air passage 12c.

[0145] Preferably the shield is made of metal or metalised plastic. It may be cylindrical in shape. It preferably has a length extending from the region of the air stream generator to at least the end of the ozone catalysing device remote from the non-thermal plasma cell and/or to at least the end of the ultraviolet (UV) radiation emitting device remote from the non-thermal plasma cell.

[0146] The shield is adapted to shield air flowing in the third passage 12c from electromagnetic emissions from the non-thermal plasma cell. It may also provide a light-proof barrier to the UV rays from the ultraviolet (UV) radiation emitting device 24.

[0147] The internal surface of the shield may be coated with a catalyst, for example titanium dioxide, to further enhance the breakdown of excess ozone, and to utilise incident UV light to produce a greater yield of hydroxyl radicals.

[0148] The shield may be used to form an electrostatic surface, able to act as an electrostatic decontamination device for the deposition of particles in the first and second air passages charged by proximity to the plasma cell. In this respect, the shield may be earthed.

[0149] A hydrocarbon delivery device is located in the third passage 12c to provide hydrocarbons to the hydrocarbon emitter using the force of the untreated air stream flowing through the third passage or by using a syphoning effect, for example.

[0150] The flow passage 12, at the air outlet 16, is terminated (at least in part) by an air turbulence creating device 64. This air turbulence creating device may be cone-shaped or trumpet-shaped: it has a vertex located upstream of its base which may be circular, square or rectangular in shape.

[0151] The effect of the air turbulence creating device is to mix the air streams coming from the first, second and third passages, and also to change the direction of these air streams such that the air may be emitted obliquely from the device, if desired. The air turbulence creating device may also be used with embodiments of the invention which do not have the third passage.

[0152] The air turbulence creating device 64 is preferably attached to the ultraviolet (UV) radiation emitting device 24 by a cap 66. The air turbulence creating device 64 may be designed and positioned such that it prevents the UV light from being externally visible by users of the device.

[0153] Referring to FIG. 6, the air decontamination device comprises the housing having flow passage 12, the air inlet to the flow passage 12 and the air outlet 16 exiting from the flow passage 12. Please note that some features have been omitted from FIG. 6 for clarity.

[0154] The air stream generator, the non-thermal plasma cell 22, the ultraviolet (UV) radiation emitting device 24, and the ozone catalysing device 26 are located in the flow passage 12. The flow passage 12 has the first (inner) passage 12a, the second (middle) passage 12b and the third (outer) passage 12c. The external surface of the first (inner) passage 12a and the internal surface of the second (middle) passage 12b are defined by the external surface of the non-thermal plasma cell and the external surface of the ozone catalysing device; a ring-shaped bridging piece (by way of example) is positioned between the non-thermal plasma cell and the ozone catalysing device to assist with the formation of the first (inner) and second (middle) passages. Shield 62 is provided between the second (middle) passage 12b and the third (outer) passage 12c.

[0155] The embodiments described above are given by way of example only, and modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims.