Patent Description:
Volatile organic compounds (VOC) are a class of organic chemicals characterized by a high vapor pressure at room temperature, typically resulting from a low boiling point. They include non-methane hydrocarbons (NMHC) and oxygenated NMHC (e.g., alcohols, aldehydes, and organic acids). VOCs emanate from off-gassing of foams, plastics, fabrics, and other manufactured products, particularly when they are new, and from the solvents in many cleaning products. VOCs are also produced as byproducts of human metabolic processes. Over <NUM> VOCs have been identified in human alveolar breath. In a closed environment full of people, such as a passenger aircraft, endogenously produced VOCs dominate.

VOCs cannot be removed by typical air filtration methods such as HEPA filtration. Existing systems to reduce VOC concentration in the cabin environment include activated carbon.

Further air contaminants can include various particulates, and can further include nitrous oxide-containing compounds that can contaminate an air supply, for example, as byproducts of production from reduction in nitrogen-containing compounds, particularly in enclosed environments, for example, due to emissions from cigarette and other tobacco-related products, emissions from e-cigarettes, the combustion of vehicle fuel, etc. that can migrate into, linger in, and otherwise accumulate in regions within and proximate to the enclosed and substantially enclosed environments, etc. Enclosed and substantially enclosed environments can include terrestrial transportation buildings, terrestrial and non-terrestrial rooms, and other substantially enclosed environments.

The Background and Technical Field sections of this document are provided to place aspects of the present disclosure in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted as prior art merely by its inclusion in the Background section.

<CIT>, according to its abstract, states a compact, lightweight, low power aircraft air filtration and VOC removal unit enables the removal of VOCs from cabin air in a passenger aircraft. A plurality of baffles having air flow-through airflow spaces are spaced apart along a duct. UV LEDs are mounted on the interior sides of the outermost baffles, and on both sides of all interior baffles. A filter module is disposed between pairs of baffles, and spaced from the baffles sufficiently to illuminate the entirety of both sides. Each filter modules comprises a plurality of filters. The filters are selected from a coarse foam, a fine foam, or a fused quartz filament felt. Each filter is loaded with a catalyst including one or more of AEROXIDE® P25, other pure titanium dioxide (TiO<NUM>), iron-doped TiO<NUM>, carbon-doped TiO<NUM>, and combinations thereof. The catalysts on the filters, under UV illumination, chemically reduce VOCs in the airflow to non-VOC molecules. discloses an air filtration unit comprising a plurality of baffles having air flow-through airflow spaces, and UV LEDs mounted on the baffles.

<CIT>, according to its abstract, states this publication discloses a filter unit connectable to a mobile communication device including a fan for generating an air flow inside the filter unit, electrodes covered with a photo catalytic material like TiO<NUM> in the air flow, UV-LEDs illuminating the electrodes, and outlet for the air flow directed in direction of user of filter unit.

<CIT>, according to its abstract, states an air purifier comprises an elongate housing comprising an air inlet and an air outlet, wherein the elongate housing has a longitudinal axis. The air purifier also includes a photocatalytic reactor and a fan configured to direct air through the elongate housing from the air inlet to the air outlet via the photocatalytic reactor in an air flow direction. The air purifier also comprises a UV light source configured to direct UV light onto the photocatalytic reactor. The photocatalytic reactor is slanted to deflect, obliquely to the longitudinal axis air flowing in the air flow direction from the air inlet to the air outlet. Further inventions are disclosed relating to a photocatalytic air purifier characterised by a first air quality sensor, a second air quality and a processor; a photocatalytic air purifier characterised by a first air outlet and a second air outlet; an air purification system characterised by a photocatalytic air purifier and a remote control comprising an air quality sensor and a wireless interface for communicating with the air purifier, and the air purifier comprises a wireless communications interface; a remote control for an air purifier and a computer-implemented air quality monitoring system and a method of monitoring air quality. discloses an air purifier having a photocatalytic reactor and a UV light source.

<CIT>, according to its abstract, states an air cleaner comprises an air moving unit (fan) creating an airflow through a channel, a photo-catalytic oxidation (PCO) element disposed in the airflow and an ultraviolet light source used to illuminate the PCO element. The light source may be Ultraviolet A (UV-A) Light Emitting Diode (LED) emitting UV light at wavelengths from <NUM> - <NUM> nanometres (nm). The PCO element may be titanium dioxide causing decomposition of water vapour in the airflow. A filter may be provided supporting the PCO element on a first face and a decomposing element on a second face. The decomposing element may be an ozone and/or volatile organic compound (VOC) decomposition element and removes odours. A particulate pre-filter may be provided. The UV LED catalyzes a reaction on the PCO element to clean the VOC decomposing element. The PCO can be a substrate comprising: a first coating comprising a VOC decomposing catalyst; a second coating comprising an ozone decomposing catalyst; and a third coating comprising titanium dioxide. An electrostatic precipitator may be disposed upstream of the PCO element. <CIT>, according to its abstract, states the utility model provides a degradation device for source gas dirt of a livestock and poultry house. Including a chamber, a photocatalyst device is arranged in the cavity; the cavity is provided with an air inlet channel and an air outlet channel. The air inlet channel is provided with a filter screen, the exhaust channel is provided with a fan, the photocatalyst device comprises at least two baffles arranged in the cavity at intervals, a photocatalyst net and an ultraviolet lamp are arranged between every two adjacent baffles, the adjacent baffles are arranged on the two sides of the inner wall of the cavity in a staggered mode, and the baffles and the wall of the cavity jointly form a one-way serpentine channel. On one hand, most dust is prevented from entering the degradation device through the filter screen in the air inlet channel; on the other hand, remaining dust is further deposited through baffles arranged on the two sides of the inner wall of the cavity in a staggered mode; one part of remaining dust impacts the lower surface of the baffle along with airflow flowing to be adsorbed, and the other part of dust freely deposits on the upper surface of the baffle, so that a photocatalyst device in the degradation device can be prevented from being blocked, and the degradation device is suitable for degrading source gas dirt of livestock and poultry houses.

An air filtration unit as recited in claim <NUM> and a method for filtering air in an enclosed environment as recited in claim <NUM> are provided.

The following presents a simplified summary of the disclosure to provide a basic understanding to those of skill in the art. This summary is not an extensive overview of the disclosure and is not intended to identify key/critical elements of aspects of the disclosure or to delineate the scope of the disclosure. The sole purpose of this summary is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

According to present aspects, air filtration apparatuses, systems, and methods are disclosed that address previous problems relating to the need to remove different types of contaminants from air contained within an enclosed or substantially enclosed environment. According to present aspects, apparatuses include, in synergistic combination, filtering and contaminant eliminating capabilities to simultaneous purify ambient air in an enclosed or substantially enclosed environment. More particularly, the presently disclosed apparatuses, systems, and methods filter or otherwise remove, in combination, from ambient air in an enclosed environment non-volatile organic compound particulates, volatile organic compounds (VOCs), and nitrous oxide-containing compounds.

According to the present disclosure, a "substantially enclosed environment" can include rooms and buildings with doors that are periodically opened, underground garages and surface garages that can retain air impurities for periods of time although entrances and exits may remain open for extended periods of time, hallways, meeting areas, meeting rooms, conference halls, as well as space stations, etc. As used herein, the term "enclosed environment" includes a "substantially enclosed environment".

According to one or more aspects of the present disclosure described and claimed herein, an air filtration unit enables the removal of particulates, including accumulated tars and other compounds resulting from, for example, smoked tobacco products, e-cigarettes, etc.; VOCs; and nitrous oxide-containing compounds from air in an enclosed environment, including where air can be directed through a duct.

According to present aspects, transverse to a longitudinal axis of an air ducts, an air filtration unit incorporating a HEPA filter, a VOC removal unit, and a nitrous oxide-containing compound removal unit is provided that can be positioned within or proximate to an air duct in order, for example, to protect the lifespan of the photocatalytic oxidation (PCO) component in the VOC removal unit.

A further aspect discloses an air filtration unit including an air duct, with the air duct including an air inlet at an air duct first end and an air outlet at an air duct second end, a high efficiency particulate air filter oriented proximate to or otherwise incorporated in the air inlet, and an airflow controller in communication with the air inlet. The air filtration unit further includes a carbon dioxide sensor in communication with the airflow controller, a pressure sensor in communication with the airflow controller. The air filtration unit includes an integrated ultraviolet light reactor located downstream from the high efficiency particulate air (HEPA) filter. The ultraviolet light reactor includes a plurality of baffles, with each baffle having a plurality of airflow spaces allowing airflow therethrough, with the baffles disposed at spaced locations within the duct between the air inlet and air outlet, and with the baffles being generally transverse to the longitudinal axis. The air filtration unit further includes a plurality of ultraviolet light emitting diodes mounted on each baffle, a porous and permeable photocatalytic oxidation filter module disposed between each pair of baffles, positioned generally transverse to the longitudinal axis, such that air flows through the photocatalytic oxidation filter module, and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), TiO<NUM> doped with carbon (C-TiO<NUM>), or combinations thereof which, when illuminated by ultraviolet light, are operative to chemically reduce volatile organic compounds to non-volatile organic compounds. The air filtration unit further includes a porous and permeable nitrous oxide-adsorbing filter that can be, for example, a nitrous oxide-containing compound adsorbing chamber comprising a nitrous oxide-containing compound adsorbent, with the adsorbent in the adsorbent filter configured into an adsorbent bed, stack, etc. The nitrous oxide-adsorbing filter is disposed downstream of the UV light reactor. The terms "air duct" and "duct" are equivalent terms that have the same meaning herein and are interchangeable.

In another aspect, the air duct comprises a longitudinal axis.

In a further aspect, the carbon dioxide sensor is in communication with a controller.

In another aspect, the carbon dioxide sensor is in communication with the air inlet.

In another aspect, the carbon dioxide sensor is in communication with at least one of the air inlet and the air outlet.

In another aspect, the pressure sensor is in communication with the air inlet.

In a further aspect, the pressure sensor is in communication with at least one of the air inlet and the air outlet.

In another aspect, the pressure sensor is in communication with the controller.

In another aspect, the porous and permeable nitrous oxide-adsorbing filter comprises a solid amine-containing adsorbent.

In another aspect, the porous and permeable nitrous oxide-adsorbing filter comprises a packed solid adsorbent, with the packed solid adsorbent comprising at least one of: a cellular monolith arrangement and a granular media arrangement.

In another aspect, the porous and permeable nitrous oxide-adsorbing filter comprises a packed solid adsorbent, with the packed solid adsorbent comprising at least one of; an amine-containing compound, a metal-organic containing compound, and a zeolite.

In a further aspect, the porous and permeable nitrous oxide-adsorbing filter is oriented proximate to the air outlet.

In another aspect, the air filtration unit is configured to be removable from the air duct for replacement.

In another aspect, the air filtration unit is configured to be replaceable.

In a further aspect, one or more components of the air filtration unit are configured to be individually removable from the air duct.

In another aspect, one or more of the high efficiency particulate air filter, the ultraviolet light reactor, the photocatalytic oxidation filter module, and the nitrous oxide-adsorbing filter can be configured to be integrated into the air filtration unit as discrete components that are configured to be removable and replaceable.

In a further aspect, the air filtration unit further comprises one or more heat sink, wherein the one or more heat sink is configured to be disposed within the duct, and with the one or more heat sink further adapted to conduct heat away from the ultraviolet light emitting diodes.

In another aspect, the plurality of ultraviolet light emitting diodes are disposed both around a periphery of each baffle and between the airflow spaces, with the plurality of ultraviolet light emitting diodes configured to maximize ultraviolet illumination of an adjacent photocatalytic oxidation filter module.

In another aspect, the plurality of ultraviolet light emitting diodes are mounted on interior sides of baffles adjacent the air inlet and outlet, and the plurality of ultraviolet light emitting diodes are mounted on both sides of baffles, with the plurality of ultraviolet light emitting diodes configured to illuminate each photocatalytic oxidation filter module from both sides.

In another aspect, the photocatalytic oxidation filter module is spaced apart from the baffles such that both surfaces of each photocatalytic oxidation filter module are illuminated by ultraviolet light.

In a further aspect, the photocatalytic oxidation filter module comprises a plurality of filters, with each filter including one or more of a coarse foam, a fine foam, a fused quartz filament felt, or combination thereof, and wherein each filter is loaded with a catalyst including one or more of pure titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), TiO<NUM> doped with carbon (C-TiO<NUM>), or combination thereof.

In another aspect, the photocatalytic oxidation filter module comprises a plurality of catalyst-loaded filters selected, arranged, and configured to maximize ultraviolet illumination of each filter and through a complete depth of each filter layer.

In another aspect, the ultraviolet light reactor comprises four baffles and three photocatalytic oxidation filter modules, and wherein the photocatalytic oxidation filter modules comprise, in order from air inlet to air outlet,.

Aspects of the present disclosure further disclose a method for filtering air in an enclosed environment, with the method including monitoring carbon dioxide concentration in an enclosed environment, initiating an air purification cycle, directing an airflow to an air inlet of an air filtering unit, with the air filtration unit including an air duct having a longitudinal axis, with the air duct comprising an air inlet at an air duct first end and an air outlet at an air duct second end, a high efficiency particulate air (HEPA) filter unit oriented proximate to the air inlet, an airflow controller in communication with the air inlet, a carbon dioxide sensor in communication with the airflow controller, and a pressure sensor in communication with the airflow controller. The air filtration unit further includes an ultraviolet light reactor, with the ultraviolet light reactor further including a plurality of baffles, with each of the plurality of baffles having a plurality of airflow spaces allowing airflow therethrough the plurality of baffles, and with the plurality of baffles disposed at spaced locations within the air duct between the air inlet and air outlet, and with the baffles being generally transverse to the longitudinal axis. The air filtration unit and the ultraviolet light reactor further includes a plurality of ultraviolet light emitting diodes mounted on each baffle, a porous and permeable photocatalytic oxidation filter module disposed between each pair of baffles, generally transverse to the longitudinal axis, such that air flows through the photocatalytic oxidation filter module, and a porous and permeable nitrous oxide-adsorbing filter disposed downstream of the UV light reactor, and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising at least one of titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), TiO<NUM> doped with carbon (C-TiO<NUM>), or combinations thereof which, when illuminated by ultraviolet light, are operative to chemically reduce volatile organic compounds in the airflow to non-volatile organic compounds. The method further includes removing an amount of particulate from the airflow upstream from the photocatalytic oxidation filter modules, illuminating the photocatalytic oxidation filter modules with ultraviolet light from ultraviolet light emitting diodes mounted on each baffle, chemically reducing volatile organic compounds in the airflow to non-volatile organic compounds, removing an amount of nitrous oxide-containing compounds from the airflow downstream from the photocatalytic oxidation filter modules where the nitrous oxide-containing compounds can be produced due to nitrogen compound reductions.

In a further aspect, a method further comprises illuminating the photocatalytic oxidation filter modules with ultraviolet light comprises disposing the ultraviolet light emitting diodes both around a periphery of each baffle and between the airflow spaces, so as to maximize the ultraviolet illumination of adjacent photocatalytic oxidation filter modules.

In another aspect, a method further comprises disposing the ultraviolet light emitting diodes on the baffles comprises disposing the ultraviolet light emitting diodes on interior sides of baffles adjacent the air inlet and outlet, and on both sides of baffles, so as to illuminate each PCO filter module from both sides.

In another aspect, a method further comprises illuminating each photocatalytic oxidation filter module with ultraviolet light comprises spacing each photocatalytic oxidation filter module apart from the baffles such that an entirety of both surfaces of each photocatalytic oxidation filter module is illuminated by ultraviolet light.

In another aspect, the method further includes conducting heat from the ultraviolet light emitting diodes away from the ultraviolet light emitting diodes via one or more heats sinks, with the one or more heat sinks disposed within the air duct.

In a further aspect, the method further includes selecting and arranging a plurality of catalyst-loaded filters to form the photocatalytic oxidation filter module so as to maximize illumination of the plurality of catalyst-loaded filters.

The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which aspects of the disclosure are shown. However, this disclosure should not be construed as limited to the aspects set forth herein.

For simplicity and illustrative purposes, the present disclosure is described by referring mainly to an exemplary aspect thereof. In the following description, numerous specific details are set forth to provide a thorough understanding of the present disclosure. However, it will be readily apparent to one of ordinary skill in the art that the aspects of the present disclosure can be practiced without limitation to these specific details. In this description, well known methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure.

Present aspects are directed to apparatuses, systems, and methods for VOC removal from air in enclosed environments that can considered to be large, enclosed environments including, for example, terrestrial environments such as, for example, rooms, transportation terminals, smoke rooms, hallways, meeting areas, meeting rooms, conference halls, as well as non-terrestrial environments including, for example, extra-terrestrial rooms, buildings, space stations, etc. In addition, further present aspects are directed to apparatuses, systems, and methods for protected VOC and nitrogen-containing compound removal from the enclosed environments disclosed herein.

<FIG> depicts an example of an air filtration and VOC removal unit <NUM> (hereinafter referred to as simply a "VOC removal unit" <NUM>), according to one aspect of the present disclosure. The VOC removal unit <NUM> operates to remove VOCs from air by photocatalytic oxidation (PCO), as will be explained in greater detail herein. The design maximizes airflow through the VOC removal unit <NUM> and minimizes heat generation and a thermal gradient across it, consistent with the maximum achievable UV illumination of PCO filters. As used herein, with respect to the present aspects, the terms "photocatalytic oxidation filter module" and "porous and permeable photocatalytic oxidation filter module" are equivalent terms and are used interchangeably.

<FIG> is a perspective view of an example VOC removal unit <NUM>, with one side removed to reveal internal components. <FIG> are sectional views of the VOC removal unit <NUM> according to one aspect, and <FIG> is a section view showing the spacing and relationship of various components.

The VOC removal unit <NUM> comprises an air inlet <NUM>, a duct <NUM> having a longitudinal axis <NUM>, and an air outlet <NUM>. In the representative aspect of the VOC removal unit <NUM> depicted in the figures, the air inlet <NUM> and outlet <NUM> have a circular cross-sectional shape, and the duct <NUM> has a square cross-section. However, those of skill in the art will readily recognize that other shapes can be utilized, within the scope of the present disclosure.

<FIG> depicts the overall operative structure of the VOC removal unit <NUM> incorporated into the present air filtration unit. A plurality of baffles <NUM> is disposed at spaced locations within the duct <NUM>. Between each pair of baffles <NUM>, a PCO filter module <NUM> comprises a plurality of filters, each of which is loaded with a photoactive catalyst. The number and spacing (as explained further below) of baffles <NUM> and PCO filter modules <NUM> is representative. In other aspects, more or fewer of each may be provided. In general, the number of baffles <NUM> will always exceed the number of PCO filter modules <NUM> by one; with baffles <NUM> disposed at both ends and in between each pair of PCO filter modules <NUM>. Ultraviolet (UV) light emitting diodes (LED) <NUM> mounted on the baffles <NUM> illuminate both sides of the filter modules <NUM> with UV light to maximize illumination of photocatalytic coatings on material in the filter modules <NUM>. Since the photocatalytic coatings require UV light as a catalyst to convert VOCs to non-VOC molecules, maximizing the illumination of PCO modules <NUM> with UV light maximizes the effectiveness of the VOC removal unit <NUM>. Cabin air directed through the VOC removal unit <NUM> passes through the baffles and PCO filter modules <NUM>. As explained further herein, UV light illuminating the PCO filter modules <NUM> photoactivates catalysts loaded therein, initiating a chemical photocatalytic oxidation process that reduces VOCs in the air to non-VOCs molecules, such as carbon dioxide and water.

The baffles <NUM> are disposed at spaced locations within the duct <NUM>, between the air inlet <NUM> and air outlet <NUM>. The baffles <NUM> are disposed generally transverse to the longitudinal axis <NUM> of the duct <NUM>. As depicted in <FIG>, each baffle <NUM> has a plurality of airflow spaces <NUM> formed in it, allowing airflow therethrough. A plurality of UV LEDs <NUM> is mounted on each baffle. The UV LEDs <NUM> are disposed both around the periphery of each baffle <NUM>, and between the airflow spaces <NUM>, so as to maximize the UV illumination of adjacent filter modules <NUM>. The UV LEDs <NUM> are mounted on the interior sides of baffles <NUM> adjacent the air inlet <NUM> and outlet <NUM> and are mounted on both sides of all other baffles <NUM>, so as to illuminate the filter modules <NUM> from both sides. Mounting UV LEDs <NUM> on all baffles <NUM> ensures maximum illumination of all filter modules <NUM>, for maximum photocatalytic effect.

The efficacy of the VOC removal unit <NUM> is greatest when the UV LEDs <NUM> are operated at high power (~<NUM> mA), thus generating a large luminous flux of UV light to activate the photoactive catalysts in the filter modules <NUM>. However, this can generate heat, which warms the air flowing through the duct <NUM>, increasing the load on aircraft air conditioning equipment. In one aspect a heat sink is connected to at least one, and preferably to each baffle <NUM> that includes LEDs <NUM>, using heat sink mounting holes <NUM>. This is done to maintain the life of the UV-LED lights by maintaining lower temperatures on their surface in low flow conditions, prolonging their life. In certain filter configurations (designed for those with higher flow rates) the heat sinks may not be necessary.

A porous and permeable PCO filter module <NUM>, comprising a plurality or "stack" of filters, is disposed between each baffle <NUM>. The PCO filter modules <NUM> are disposed generally transverse to the longitudinal axis <NUM> of the duct <NUM>, such that air flows through the PCO filter module <NUM>. Each PCO filter module <NUM> contains one or more catalysts which, when illuminated by UV light, are operative to chemically reduce VOCs to non-VOC molecules. Maximum UV illumination of all filters in each filter module <NUM> is thus desired, to maximize the efficacy of VOC removal. Accordingly, the PCO filter modules <NUM> are spaced apart from the baffles such that the entirety of both surfaces of each PCO filter module is illuminated by UV light.

If a PCO filter module <NUM> were directly adjacent a baffle <NUM>, only spots on the surface of the PCO filter module <NUM> that contact a UV LED <NUM> would be illuminated. As the spacing between the PCO filter module <NUM> and the baffle <NUM> increases, the illumination spot sizes increase, and the photonic efficiency decreases. The optimal spacing is that distance at which the illumination spots just overlap, fully illuminating the entire facing surface of the PCO filter module <NUM>, increasing the spacing beyond this distance reduces the luminous flux of UV light. In the aspect depicted in <FIG>, the distance between each face of a filter module <NUM> and the facing baffle <NUM> is <NUM> (dimension "b"); at this distance, 500mA of power applied to the UV LEDs <NUM> yields a light intensity of over 20mW/cm<NUM>. The filter modules <NUM> in this aspect are <NUM> thick (dimension "c"). In the aspect depicted, the baffles <NUM>, measured to the outermost protruding UV LEDs <NUM>, are <NUM> thick for those adjacent to the air inlet <NUM> and outlet <NUM>, which have UV LEDs <NUM> mounted on only the interior-facing sides (dimension "a"), and <NUM> thick for interior baffles <NUM>, which have UV LEDs <NUM> mounted on both sides (dimension "a*"). These dimensions are exemplary. Present aspects contemplate alternate relative spacing of components for VOC removal units of different size or shape.

The filters in each PCO filter module <NUM> are loaded with some form of titanium dioxide (TiO<NUM>). Photocatalytic oxidation occurs in the VOC removal unit <NUM> by illuminating the TiO<NUM> in the filters with UV light, generating hydroxyl radicals (OH•) by reaction with water molecules in the air. The free radicals, in turn, oxidize VOCs into non-VOC molecules - primarily carbon dioxide (CO<NUM>) and water (H<NUM>O). These are returned to the airflow, avoiding the accumulation of contaminants.

Titanium dioxide is a light-sensitive semiconductor, which adsorbs electromagnetic radiation in the near UV region. The most common natural form of TiO<NUM> is the mineral rutile. Other forms of TiO<NUM> are anatase (also known as octahedrite) and brookite (an orthorhombic mineral). TiO<NUM>, when used as a photoactive catalyst, is primarily anatase, with a small amount of rutile. The anatase form of TiO<NUM> requires higher light energy than the rutile form and shows a stronger photoactivity. The energy difference between the valence and the conductivity bands of a TiO<NUM> molecule in the solid state is <NUM>. 05eV for rutile and <NUM>. 29eV for anatase, corresponding to a photonic absorption band at <<NUM> for rutile and <<NUM> for anatase.

Absorption of light energy causes an electron to be promoted from the valence band to the conduction band. This electron, and the simultaneously created positive "electron hole," can move on the surface of the solid, where it can take part in redox reactions. In particular, water molecules in vapor state in the air are adsorbed onto the TiO<NUM> surface where they react with the free electron, generating hydroxyl radicals (OH•). These radicals are uncharged, short-lived, highly reactive forms of hydroxide ions (OH-), bearing considerable oxidizing power. The OH• radicals can cause complete oxidation of organic compounds to carbon dioxide and water. In some aspects, the OH• radicals reduce VOCs to the following end products:.

Although the primary application of photocatalytic oxidation in the VOC removal unit <NUM> is to reduce VOCs into non-VOC molecules, the process also kills contaminants in bioaerosols, such as bacteria, molds, and fungus. In general, reduction of VOC levels in cabin air enhances comfort of passengers.

The photoactivity of TiO<NUM> is known and has commercial applications. AEROXIDE® P25 is a nanostructured, fine-particulate pure titanium dioxide with high specific surface area. The product, available from Evonik Industries of Parsippany, NJ. (AEROXIDE® P25), is a fine white powder with hydrophilic character caused by hydroxyl groups on the surface. It consists of aggregated primary particles. The aggregates are several hundred nm in size and the primary particles have a mean diameter of approximately <NUM>. The Brunner-Emmett-Teller (BET) theory can be used to measure the surface area of the solid or porous material selected, optionally in conjunction with transmission electron microscopy (TEM) imaging to confirm pore size. Further, pore size distribution can be evaluated by Barrett-Joyner-Halenda (BJH) interpretation. The weight ratio of anatase to rutile is approximately <NUM>/<NUM>. AEROXIDE® P25 is sold commercially as a photoactive catalyst. With its high purity, high specific surface area, and combination of anatase and rutile crystal structure, AEROXIDE® P25 is widely used for catalytic and photocatalytic applications. Other forms of pure TiO<NUM> may also be used in PCO filter modules <NUM> in the VOC removal unit <NUM>.

Additionally, the inventors have found that doping TiO<NUM> with iron (Fe-TiO<NUM>) and carbon (C-TiO<NUM>) yield superior photocatalytic results. The UV-PCO reactor relies on adsorption of the organic compounds onto the surface of the catalyst to enable breakdown of the compounds. Doping the TiO<NUM> with carbon or iron increases the sorption capacity of the catalyst, which allows for greater removal of VOCs from the airstream. Through doping with metal and non-metal agents the band gap energy level of TiO<NUM> is lowered and electron-hole pair mechanism is kept constant with a longer duration for higher light absorption capability which results in better efficiency.

Table <NUM> below lists pre- and post-filtering concentrations of various representative VOCs (i.e., ethanol, or EtOH; acetone; and limonene) for pure TiO<NUM>, Fe-TiO<NUM>, and C-TiO<NUM>, when loaded onto various filter media types. It is clear from these data that Fe-TiO<NUM>, and C-TiO<NUM> provide superior VOC removal results, as compared to pure TiO<NUM>.

The photoactive catalyst - whether AEROXIDE® P25 (considered to be a "pure TiO<NUM>" according to the present disclosure), other pure TiO<NUM>, Fe-TiO<NUM>, or C-TiO<NUM> - is loaded into a porous and air- and light-permeable filter. In one aspect, the photoactive catalyst is adhered to all surface area of the filter, including within pores and passages running throughout the volume of the filter medium. In at least one aspect, the catalyst is deposited by a dip coating method, followed by drying at <NUM> -<NUM>. Other methods of catalyst deposition may be used.

The type of substrate and coating methods have important effects on coating stability, photocatalytic, and mechanical performance of the filters. Porous metal substrates offer better toughness, better malleability, and lower cost than ceramic substrates. However, using metal substrate generally results in peeling coatings with cracks. This occurs at heating stage and due to difference in thermal expansion coefficients between the TiO<NUM> and the substrate metal.

Porous TiO<NUM> filters are commonly employed to avoid this problem. Such filters are commonly prepared by coating a TiO<NUM> sol, slurry, or precursor liquid onto ceramic substrates, metal meshes or ceramic or metallic foam by different coating methods. After coating application, heat treatment necessary for photocatalysts activity around <NUM> is generally conducted.

In one aspect, three filter types are used in PCO filter modules <NUM>: coarse foam, fine foam, and fused quartz filament felt. Both the porosity (number and size of pores, or voids) and the permeability (ability of fluid to flow through, which is related to interconnectivity of the pores) of each type of filter type are selected based on a contemplated use relative to VOCs of interest. The Brunner-Emmett-Teller (BET) theory can be used to measure the surface area of the solid or porous material selected, optionally in conjunction with transmission electron microscopy (TEM) imaging to confirm pore size. Further, pore size distribution can be evaluated by Barrett-Joyner-Halenda (BJH) interpretation. Porosity contributes to the surface area for adhering more photocatalytic coatings. Permeability impacts the selected volume of air that can flow through the PCO filter modules <NUM> to remove VOCs from the cabin air of a large aircraft, for example.

The coarse foam is a relatively open foam, with average pores size of approximately <NUM>, and high permeability. The coarse foam filter is approximately <NUM> thick. A suitable coarse foam is available from Recemat BV of the Netherlands. This material can be uniformly coated with catalyst. The coarse foam filter allows much of the incident UV light to penetrate the foam, thus illuminating successive filters. For this reason, in some aspects, a coarse foam filter is at both exterior positions of a "stack" of filters forming a PCO filter module <NUM>. The position of coarse foam filter is also maintained on the outside of whole filter stack to start the VOC degradation in a lower specific surface area to very high specific surface area in fine foam filters.

The fine foam is a denser foam, with average pores size of approximately <NUM>, and lower permeability as compared to coarse foam but with a higher surface area. The Brunner-Emmett-Teller (BET) theory can be used to measure the surface area of the solid or porous material selected, optionally in conjunction with transmission electron microscopy (TEM) imaging to confirm pore size. Further, pore size distribution can be evaluated by Barrett-Joyner-Halenda (BJH) interpretation. Accordingly, the fine foam filter is thinner than the coarse foam filter, at approximately <NUM>-<NUM>, to maintain robust airflow. This material is more difficult to coat uniformly with catalyst. A suitable fine foam is available from Alantum GMBH of Germany.

Another type of material is made from fused quartz filaments. A suitable felt of this type is QUARTZEL® felt, available from Magento of the USA. The QUARTZEL® felt is difficult to coat uniformly and presents a high resistance to air flow. Accordingly, it is used sparingly. In one aspect, only one of three PCO filter modules <NUM> in a VOC removal unit <NUM> include a fused quartz filament filter, and that module <NUM> includes only a single such filter. Each PCO filter module <NUM> comprises a plurality of catalyst-loaded filters selected and arranged to maximize UV illumination of all of the filters. That is, according to present aspects, in the present air filtration unit, the photocatalytic oxidation filter module comprises a plurality of catalyst-loaded filters selected and arranged to maximize ultraviolet illumination of each filter and through a complete depth of each filter layer.

With, in some aspects, three filter media and four types of photoactive catalysts, there are a dozen combinations of PCO filters from which to select. The number of permutations of which of these filters to stack into a filter module <NUM>, in which order, is very large. Furthermore, different PCO filter modules. That is, different selections and arrangements of photoactive-catalyst-loaded filters can be placed in different locations along the duct <NUM> of the VOC removal unit <NUM>.

In one aspect, as depicted in <FIG>, an air filtration and volatile organic compound (VOC) removal unit <NUM> includes an air duct <NUM> having a longitudinal axis <NUM>, an air inlet <NUM> at one end, and air outlet <NUM> at the other end; a plurality of baffles <NUM> (<FIG>), each having a plurality of open spaces <NUM> allowing airflow therethrough, disposed at spaced locations within the duct <NUM> between the air inlet <NUM> and air outlet <NUM>, the baffles <NUM> being generally transverse to the longitudinal axis <NUM>; a plurality of ultraviolet (UV) light emitting diodes (LED) <NUM> mounted on each baffle <NUM>; and a porous and permeable photocatalytic oxidation (PCO) filter module <NUM> disposed between each pair of baffles <NUM>, generally transverse to the longitudinal axis <NUM>, such that air flows through the PCO filter module <NUM>. Each PCO filter module <NUM> contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), TiO<NUM> doped with carbon (C-TiO<NUM>), or combinations thereof, which, when illuminated by UV light, are operative to chemically reduce VOCs to non-VOC molecules. This provides a compact, lightweight, low-power means for removing VOCs.

In one aspect, the VOC removal unit further includes one or more heat sinks disposed within the duct and adapted to conduct heat away from the UV LEDs away and maintain their lifespan. This prevents overheating of the LEDs to prolong their life in a low flow situation.

In one aspect, the UV LEDs are disposed both around a periphery of each baffle and between the airflow spaces so as to maximize the UV illumination of adjacent PCO filter modules. The UV LEDs are mounted on interior sides of baffles adjacent the air inlet and outlet and are mounted on both sides of all other baffles, so as to illuminate the PCO filter modules from both sides. The PCO filter modules are spaced apart from the baffles such that the entirety of both surfaces of each PCO filter module is illuminated by UV light. These features ensure maximum and even illumination of the PCO filter modules by UV light.

Each PCO filter module comprises a plurality of filters, each filter selected from the group consisting of a coarse foam, a fine foam, and a fused quartz filament felt, and each filter is loaded with a catalyst which may be one or more of pure titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), and TiO<NUM> doped with carbon (C-TiO<NUM>), and combinations thereof. In one aspect, each PCO filter module comprises a plurality of catalyst-loaded filters selected and arranged to maximize UV illumination of all of the filters. These materials have high durability and the arrangements facilitate the removal of VOCs.

The VOC removal unit <NUM> comprises four baffles <NUM> and three PCO filter modules <NUM>. The PCO filter modules <NUM> comprise, in order from air inlet <NUM> to air outlet <NUM>,.

In another aspect, with the same numbers of baffles <NUM> and PCO filter modules <NUM>, the PCO filter modules <NUM> comprise, in order from air inlet <NUM> to air outlet <NUM>,.

Based on the information disclosed herein, those of skill in the art may devise numerous other selections and arrangements of both photoactive catalyst-loaded filters in each PCO filter module <NUM>, and the PCO filter modules <NUM> in the VOC removal unit <NUM>, within the scope of the present disclosure.

According to further aspects, <FIG> shows an exemplary air purification system and apparatus that can implement the PCO filter modules of the types shown, for example, in <FIG>, in combination with presently disclosed selected additional filter system components integrated into the system to further enhance particulate removal (including non-VOC particulate removal) upstream from the PCO filter modules, and further effect nitrous oxide-containing compound removal from an airflow downstream from the PCO filter modules. According to present aspects, placement of an HEPA filter upstream of the UV-PCO portion of the present air filtration unit removes tar/particles from the airflow directed into the present air filtration unit that may otherwise impact the surfaces of the PCO, and that could substantially reduce the efficiency of the ultraviolet light reactor(s).

According to present aspects, nitrous oxide (NO<NUM>, NOx, NO) adsorbent such as, for example, an amine adsorbent, is oriented in the nitrous oxide-adsorbing filter downstream of the ultraviolet light reactor(s), as nitrous oxides are a byproduct of reactions between ammonia (a product of, for example, smoking), and oxygen in the presence of ultraviolet light. Likewise, nitrous oxides are also highly present within indoor enclosed environments including, for example, an airport, a bus terminal, a railway terminal, a planetary habitat, and other terrestrial transportation environments, etc. To further purify ambient air in such environments, present aspects reduce the exposure to nitrous oxide-containing compounds as the contemplated nitrous oxide removal region, including a nitrous oxide-adsorbing filter, in the presently disclosed air purification unit significantly reduces the nitrous oxide concentrations in the ambient air present in, for example, an occupied area of a terrestrial transportation environment including, for example, an airport, a smoking room in an airport, etc..

As shown in <FIG>, according to present aspects, an air filtration apparatus <NUM> incorporates a filter <NUM> that can be a high-efficiency particulate air HEPA filter located proximate to or otherwise incorporated into an air inlet <NUM> of a VOC removal unit 10a of the type shown in <FIG> and described herein. According to present aspects, the HEPA filter is oriented upstream of the VOC removal unit 10a. HEPA filters are also known as high-efficiency particulate adsorbing and high-efficiency particulate arresting filters representing an efficiency standard of air filter. Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove from the air passing therethrough of at least <NUM>% (European Standard) or <NUM>% (ASME, U. ) of particles having a diameter equal to <NUM> or greater, with the filtration efficiency increasing for particle diameters both less than and greater than <NUM>.

According to present aspects, HEPA filters can comprise a mat of ordered or randomly arranged fibers. The fibers can include fiberglass having diameters between <NUM> and <NUM>. The air space between HEPA filter fibers is typically much greater than <NUM>. Unlike sieves or membrane filters, where particles smaller than openings or pores can pass through, HEPA filters are designed to target a range of particle sizes. These particles are trapped (they stick to a fiber) through a combination of the mechanisms including diffusion, interception, and impaction. As used in accordance with the present aspects, and as shown in <FIG>, airflow introduced into the air filtration apparatuses and systems first encounters the HEPA filter that is located upstream from the VOC removal unit 10a for the purpose of removing particulates from the introduced airflow upstream of the VOC removal unit that incorporates the PCO filter modules (that, in turn, employ the UV photocatalysis) with the VOC removal unit being primarily responsible for the subsequent removal of VOCs from the airflow flowing through the unit.

According to present aspects, the disclosed apparatuses, systems, and methods can implement a variable speed or diverted air system based upon the CO<NUM> of the occupied space in an enclosed environment to minimize exposure of the air purifier to contaminants; having the potential to increase the lifespan of the technology and minimize maintenance costs. When the NOx is primarily produced within the unit during operation, diverting an airflow can assist in preventing the exposure of the unit to a selected level of CO<NUM> that can be directed into the air filtration unit from the occupied space in, for example, an enclosed environment.

<FIG> shows an airflow controller <NUM> that is in communication with a first and second carbon dioxide (CO<NUM>) sensors <NUM>, 206a, respectively, with the CO<NUM> sensors <NUM>, 206a further comprising or otherwise in communication with first and second pressure sensors <NUM>, 208a respectively incorporated into or proximate to the air inlet <NUM>. Pressure sensors <NUM>, 208a are in communication with airflow controller <NUM> with the pressure sensors <NUM>, 208a configured to monitor and determine changes in system pressures, with the pressure sensors <NUM>, 208a further able to monitor the performance of the HEPA filter, for example, to output information regarding to potential clogging of, for example, a HEPA filter.

As shown in <FIG>, the airflow controller can initiate, terminate, modify, and otherwise direct and control air in a surrounding environment to form an airflow into the air filtration apparatus <NUM>. Air in a surrounding environment can include air that is, for example, within an enclosed environment, and the enclosed environment can be, for example, a room in a building, a terminal, a warehouse etc., and that can be an enclosed environment in or proximate to a terrestrial transportation environment such as, for example, an airport terminal, a railway terminal, a bus terminal, a raceway, etc..

While the presently disclosed particulate and VOCs removed from ambient air in a particular surrounding can accomplish a certain desired level of purification of ambient air, as shown in <FIG>, the air filtration unit <NUM> further comprises a nitrous oxide-adsorbing filter <NUM> that can be a porous and permeable nitrous oxide-adsorbing chamber further comprising, for example, a bed, stack etc. that is disposed downstream from the VOC removal unit 10a for the purpose of removing nitrous oxide-containing compounds from the air directed through the air filtration apparatus. The nitrous oxide-containing compounds that can be adsorbed by the nitrous oxide-adsorbing filter can include, for example, NO<NUM>, NOx, NO. The nitrous oxide-adsorbing filter can be oriented within the air filtration unit at a point downstream from the VOC removal unit, and can be located proximate to the air outlet, or otherwise incorporated into the air outlet.

The nitrous oxide-adsorbing filter can include a solid form amine-containing packed bed, a cellular monolith, a granular media set-up, etc., and the nitrous oxide-adsorbing filter can have a separate frame housing the nitrous oxide-adsorbing filter, or the frame can be built into or otherwise incorporated and formed as a part of (e.g., integral with) the air filtration unit air outlet. The amine will be immobilized into a solid form (e.g., a monolithic contractor), rather than utilizing a liquid membrane. While amines and amine-containing compounds are contemplated for use in the nitrous oxide-adsorbing filter, other potential nitrous oxide adsorbents can include metal organic compounds, zeolites, etc., alone or in combination.

<FIG> shows an end view of the air filtration unit <NUM> showing the air inlet <NUM> framed by duct <NUM>. <FIG> shows an end view of the air outlet end of a presently disclosed air filtration unit <NUM>, with the air outlet <NUM> framed by the duct <NUM>. While the air intake is shown in a circular configuration and the duct perimeter and air outlet are shown as substantially square, it is understood that presently disclosed filtration units can be configured into any geometry as desired and according to the constraints presented by ducts in ductwork, including ducts that can be pre-existing ducts into which the presently disclosed air filtration units can be retrofitted, for example.

<FIG>, <FIG>, <FIG>, <FIG> are flowcharts showing exemplary methods implementing the apparatuses and systems shown at least in <FIG>, <FIG>, <FIG>.

As shown in <FIG>, a presently disclosed method is disclosed for filtering air in an enclosed environment, with the method <NUM> including monitoring <NUM> carbon dioxide concentration in an enclosed environment, initiating <NUM> an air purification cycle, directing <NUM> an airflow to an air inlet of an air filtration unit, with the air filtration unit including an air duct having a longitudinal axis, said air duct comprising an air inlet at a first end and an air outlet at a second end, a high efficiency particulate air (HEPA) filter unit oriented proximate to the air inlet, an airflow controller in communication with the air inlet, a carbon dioxide sensor in communication with the airflow controller, and a pressure sensor in communication with the airflow controller. The air filtration unit further includes an ultraviolet light reactor that further includes a plurality of baffles, with each baffle having a plurality of airflow spaces allowing airflow therethrough, disposed at spaced locations within the duct between the air inlet and air outlet, and with the baffles being generally transverse to the longitudinal axis. The air filtration unit further includes a plurality of ultraviolet light emitting diodes mounted on each baffle, a porous and permeable photocatalytic oxidation filter module disposed between each pair of baffles, generally transverse to the longitudinal axis, such that air flows through the photocatalytic oxidation filter module, and a porous and permeable nitrous oxide-adsorbing filter disposed downstream of the UV light reactor, and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), TiO<NUM> doped with carbon (C-TiO<NUM>), or combinations thereof which, when illuminated by ultraviolet light, are operative to chemically reduce volatile organic compounds to non-volatile organic compounds. The method further includes removing <NUM> an amount of particulate from the airflow upstream from the photocatalytic oxidation filter modules, illuminating <NUM> the photocatalytic oxidation filter modules with ultraviolet light from ultraviolet light emitting diodes mounted on each baffle, chemically reducing <NUM> volatile organic compounds in the airflow to non-volatile organic compounds (thus removing VOCs from the airflow), and removing <NUM> an amount of nitrous oxide-containing compounds from the airflow downstream from the photocatalytic oxidation filter modules and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), or TiO<NUM> doped with carbon (C-TiO<NUM>) which, when illuminated by UV light, are operative to chemically reduce volatile organic compounds in the airflow to non-volatile organic compounds.

<FIG> is a flowchart outlining a presently disclosed method for filtering air in an enclosed environment, with the method <NUM> including monitoring <NUM> carbon dioxide concentration in an enclosed environment and monitoring <NUM> pressure of the system for the purpose of sensing a pressure drop indicating a need for adjusting a system airflow capacity, for example. The pressure can be monitored at an air intake or an air outlet, with the pressure monitored by a sensor that can send a signal to a controller that can adjust airflow capacity through the unit and system, etc..

Method <NUM> shown in <FIG> further shows initiating <NUM> an air purification cycle, directing <NUM> an airflow to an air inlet of an air filtration unit, with the air filtration unit including an air duct having a longitudinal axis, said air duct comprising an air inlet at a first end and an air outlet at a second end, a high efficiency particulate air (HEPA) filter unit oriented proximate to the air inlet, an airflow controller in communication with the air inlet, a carbon dioxide sensor in communication with the airflow controller, and a pressure sensor in communication with the airflow controller. The air filtration unit further includes an ultraviolet light reactor that further includes a plurality of baffles, with each baffle having a plurality of airflow spaces allowing airflow therethrough, disposed at spaced locations within the duct between the air inlet and air outlet, and with the baffles being generally transverse to the longitudinal axis. The air filtration unit further includes a plurality of ultraviolet light emitting diodes mounted on each baffle, a porous and permeable photocatalytic oxidation filter module disposed between each pair of baffles, generally transverse to the longitudinal axis, such that air flows through the photocatalytic oxidation filter module, and a porous and permeable nitrous oxide-adsorbing filter disposed downstream of the UV light reactor, and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), TiO<NUM> doped with carbon (C-TiO<NUM>), or combinations thereof which, when illuminated by ultraviolet light, are operative to chemically reduce volatile organic compounds to non-volatile organic compounds. The method further includes removing <NUM> an amount of particulate from the airflow upstream from the photocatalytic oxidation filter modules, illuminating <NUM> the photocatalytic oxidation filter modules with ultraviolet light from ultraviolet light emitting diodes mounted on each baffle, chemically reducing <NUM> volatile organic compounds in the airflow to non-volatile organic compounds (thus removing VOCs from the airflow), and removing <NUM> an amount of nitrous oxide-containing compounds from the airflow downstream from the photocatalytic oxidation filter modules and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), or TiO<NUM> doped with carbon (C-TiO<NUM>) which, when illuminated by UV light, are operative to chemically reduce volatile organic compounds in the airflow to non-volatile organic compounds.

<FIG> is a flowchart outlining a presently disclosed method for filtering air in an enclosed environment, with the method <NUM> including monitoring <NUM> carbon dioxide concentration in an enclosed environment, monitoring <NUM> pressure of the system for the purpose of sensing a pressure drop indicating that the need for adjusting a system airflow capacity, for example. The pressure can be monitored at an air intake or an air outlet, with the pressure monitored by a sensor that can send a signal to a controller that can adjust airflow capacity through the unit and system, etc..

Method <NUM> shown in <FIG> further shows initiating <NUM> an air purification cycle, directing <NUM> an airflow to an air inlet of an air filtration unit, with the air filtration unit including an air duct having a longitudinal axis, said air duct comprising an air inlet at a first end and an air outlet at a second end, a high efficiency particulate air (HEPA) filter unit oriented proximate to the air inlet, an airflow controller in communication with the air inlet, a carbon dioxide sensor in communication with the airflow controller, and a pressure sensor in communication with the airflow controller. The air filtration unit further includes an ultraviolet light reactor that further includes a plurality of baffles, with each baffle having a plurality of airflow spaces allowing airflow therethrough, disposed at spaced locations within the duct between the air inlet and air outlet, and with the baffles being generally transverse to the longitudinal axis. The air filtration unit further includes a plurality of ultraviolet light emitting diodes mounted on each baffle, a porous and permeable photocatalytic oxidation filter module disposed between each pair of baffles, generally transverse to the longitudinal axis, such that air flows through the photocatalytic oxidation filter module, and a porous and permeable nitrous oxide-adsorbing filter disposed downstream of the UV light reactor, and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), TiO<NUM> doped with carbon (C-TiO<NUM>), or combinations thereof which, when illuminated by ultraviolet light, are operative to chemically reduce volatile organic compounds to non-volatile organic compounds. The method further includes removing <NUM> an amount of particulate from the airflow upstream from the photocatalytic oxidation filter modules, illuminating <NUM> the photocatalytic oxidation filter modules with ultraviolet light from ultraviolet light emitting diodes mounted on each baffle, chemically reducing <NUM> volatile organic compounds in the airflow to non-volatile organic compounds (thus removing VOCs from the airflow), and removing <NUM> an amount of nitrous oxide-containing compounds from the airflow downstream from the photocatalytic oxidation filter modules and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), or TiO<NUM> doped with carbon (C-TiO<NUM>) which, when illuminated by UV light, are operative to chemically reduce volatile organic compounds in the airflow to non-volatile organic compounds. Method <NUM>, shown <FIG> further includes conducting <NUM> heat away from LEDs via at least one heat sink, with the at least one heat sink disposed within the duct and adapted to conduct heat away from the UV LEDs away and maintain the lifespan of the UV LEDs to, for example, prevent overheating of the UV LEDs and prolong the life of the UV LEDs (e.g., in a low airflow situation).

Method <NUM> shown in <FIG> further shows initiating <NUM> an air purification cycle, directing <NUM> an airflow to an air inlet of an air filtration unit, with the air filtration unit including an air duct having a longitudinal axis, said air duct comprising an air inlet at a first end and an air outlet at a second end, a high efficiency particulate air (HEPA) filter unit oriented proximate to the air inlet, an airflow controller in communication with the air inlet, a carbon dioxide sensor in communication with the airflow controller, and a pressure sensor in communication with the airflow controller. The air filtration unit further includes an ultraviolet light reactor that further includes a plurality of baffles, with each baffle having a plurality of airflow spaces allowing airflow therethrough, disposed at spaced locations within the duct between the air inlet and air outlet, and with the baffles being generally transverse to the longitudinal axis. The air filtration unit further includes a plurality of ultraviolet light emitting diodes mounted on each baffle, a porous and permeable photocatalytic oxidation filter module disposed between each pair of baffles, generally transverse to the longitudinal axis, such that air flows through the photocatalytic oxidation filter module, and a porous and permeable nitrous oxide-adsorbing filter disposed downstream of the UV light reactor, and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), TiO<NUM> doped with carbon (C-TiO<NUM>), or combinations thereof which, when illuminated by ultraviolet light, are operative to chemically reduce volatile organic compounds to non-volatile organic compounds. The method further includes removing <NUM> an amount of particulate from the airflow upstream from the photocatalytic oxidation filter modules, illuminating <NUM> the photocatalytic oxidation filter modules with ultraviolet light from ultraviolet light emitting diodes mounted on each baffle, chemically reducing <NUM> volatile organic compounds in the airflow to non-volatile organic compounds (thus removing VOCs from the airflow), and removing <NUM> an amount of nitrous oxide-containing compounds from the airflow downstream from the photocatalytic oxidation filter modules and wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), or TiO<NUM> doped with carbon (C-TiO<NUM>) which, when illuminated by UV light, are operative to chemically reduce volatile organic compounds in the airflow to non-volatile organic compounds. Method <NUM> further includes selecting and arranging <NUM> a plurality of catalyst-loaded filters in the photocatalytic oxidation (PCO) component in the VOC removal unit to maximize illumination of the catalyst-loaded filters.

The method <NUM>, though not shown in <FIG>, can further include (as shown in method <NUM> shown in <FIG>) conducting <NUM> heat away from LEDs via at least one heat sink, with the at least one heat sink disposed within the duct and adapted to conduct heat away from the UV LEDs away and maintain the lifespan of the UV LEDs to, for example, prevent overheating of the UV LEDs and prolong the life of the UV LEDs (e.g., in a low airflow situation).

According to present aspects, the airflow rates of air delivered through the present air filtration units, and according to presently disclosed methods, can be, for example, from about <NUM> to about <NUM>/m<NUM> (about <NUM> to about <NUM> ft<NUM>/minute (CFM)) per occupant of purified airflow, with the understanding that the overall unit and system sizing and scale can be configured to accommodate and service enclosed environments (e.g., rooms, hallways, buildings, warehouses, garages, terrestrial transportation building environments, etc.).

Present apparatuses, systems, and methods are further understood to monitor, determine, and respond to CO<NUM> levels determined by the CO<NUM> sensors, and the system pressures observed, monitored, and detected by the pressure sensors. The combined factors of sensed CO<NUM> in an environment, and the changes in sensed CO<NUM> levels while the present systems are in operation, and further in view of sensed system pressures, can be relayed to one or more airflow controllers to adjust, in real time, airflow to be directed into the present systems.

Claim 1:
An air filtration unit (<NUM>) comprising:
an air duct (<NUM>), said air duct comprising an air inlet (<NUM>) at a first end and an air outlet (<NUM>) at a second end;
a high efficiency particulate air filter (<NUM>) oriented proximate to the air inlet;
an airflow controller (<NUM>) in communication with the air inlet;
a carbon dioxide sensor (<NUM>) (206a) in communication with the airflow controller;
a pressure sensor (<NUM>) in communication with the airflow controller;
an ultraviolet light reactor (10a), the ultraviolet light reactor comprising; a plurality of baffles (<NUM>), each having a plurality of airflow spaces allowing airflow therethrough, disposed at spaced locations within the duct between the air inlet and air outlet, the baffles being generally transverse to the longitudinal axis;
a plurality of ultraviolet light emitting diodes (<NUM>) mounted on each baffle;
a porous and permeable photocatalytic oxidation filter module (<NUM>) disposed between each pair of baffles, generally transverse to the longitudinal axis, such that air flows through the photocatalytic oxidation filter module;
a porous and permeable nitrous oxide-adsorbing filter (<NUM>) disposed downstream of the ultraviolet light reactor; and
wherein each photocatalytic oxidation filter module contains one or more catalysts comprising titanium dioxide (TiO<NUM>), TiO<NUM> doped with iron (Fe-TiO<NUM>), TiO<NUM> doped with carbon (C-TiO<NUM>), or combinations thereof which, when illuminated by ultraviolet light, are operative to chemically reduce volatile organic compounds to non-volatile organic compounds.