Air purifier

Disclosed is a chemical and biological air purifier. The air purifier has a housing having an inlet and an outlet both aligned on a longitudinal axis, a turbulence generator, one or more vacuum ultraviolet (UV) sources achieving a chemical purification and one or more germicidal ultraviolet (UV) sources achieving the biological purification. The turbulence generator is mounted within the housing downstream of the inlet and promotes a dispersion and mixing of air received through the inlet. The vacuum UV source is mounted within the housing downstream of the turbulence generator and breaks oxygen molecules into mono-atomic oxygen which then reacts with chemical contaminants present in the air and degrades them by successive oxidation to odorless and inoffensive byproducts. The turbulence generator reduces the production of ozone by increasing the contact between the mono-atomic oxygen and the chemical contaminants. The germicidal UV-C source is mounted within the housing parallel to the longitudinal axis of the housing downstream of the vacuum UV source. The germicidal UV-C source, in use, kills biological contaminants present in the air by irradiation and degrades residual ozone produced by the vacuum UV sources into molecular oxygen, thereby purifying air from the biological contaminants and residual ozone.

FIELD OF THE INVENTION 
The present invention relates to an air purifier used to purify air from 
chemical and biological air contaminants. 
BACKGROUND OF THE INVENTION 
Indoor air quality problems, often referred to as "Sick Building Syndrome" 
costs North America well over 100 Billion dollars each year in health 
care, absenteeism, lost production time and lost revenue. 
Studies have demonstrated that the air inside businesses and homes can be 
more contaminated than the outside air of some industrialized cities. 
Contaminants have generally been classified into two categories: chemical 
contaminants and biological contaminants. 
CHEMICAL CONTAMINANTS 
Most chemical contaminants found in buildings arise from the increasing use 
of synthetic materials such as pressed wood, nylon carpets, plastics, 
solvents and other household maintenance products. 
The characteristics of a few common chemical contaminants and their effects 
on health are summarized in table 1, which is derived from the American 
Conference of Governmental Industrial Hygienists (ACGIH 1989). 
TABLE 1 
______________________________________ 
Chemical Major indoor 
contaminant Health effects 
sources 
______________________________________ 
Formaldehyde Nausea, Furniture, 
eye irritation, 
carpets, 
headaches, synthetic panels, 
confusion plywood, 
press wood, 
insulation 
Carbon monoxide 
Headaches, Cigarette, 
nausea, cooking smoke 
fatigue 
Benzene Nausea, Paint, 
nose irritation, 
synthetic materials, 
headaches printing inks 
Toluene Nausea, Paint, 
nose irritation, 
solvents, 
headaches nail polish 
Hydrocarbons (VOC) 
Nausea, Oils, 
headaches fuels, 
greases, 
fireplace, 
cigarette 
Aerosols Eye irritation, 
Hair spray, 
nausea, deodorants 
headaches 
______________________________________ 
BIOLOGICAL CONTAMINANTS 
Microorganisms represent the major source of biological contaminants. 
Viruses, bacteria, fungi and protozoa, as well as their by-products, such 
as antigens, mycotoxins and bacterial endotoxins are commonly found in 
buildings or workplaces. 
The characteristics of a few common biological contaminants, their effects 
on health as well as their major indoor source are summarized in table 2. 
TABLE 2 
______________________________________ 
Biological Major indoor 
contaminants Health effects 
sources 
______________________________________ 
Bacteria Pneumonia, Water reservoir, 
fever, hot water, 
hypersensitivity, 
hot surface, 
asthma, humidifier 
pneumonitis 
Fungi, Asthma, Outdoor air, 
fungal spores 
rhinitis, spores, 
mycosis, animals, 
mycotoxicosis, 
plant, 
damp surface 
Protozoa Infections Water reservoir, 
humidifier, 
Viruses Infections Water reservoir, 
humidifier 
Algae Asthma, Outdoor air 
Rhinitis 
Pollen Asthma, Outdoor air, 
Rhinitis, green plants 
hypersensitivity 
Arthropods, Asthma, Carpet, 
antigens Rhinitis feces, 
mattress, 
dust, 
animals 
Antigens from 
Asthma, animal hair, 
mammals Rhinitis, skin scale, 
Hypersensitivity 
saliva 
______________________________________ 
Most environments contain a large variety of bacteria. It is generally 
acknowledged that health risks increase only with the increase of pathogen 
bacteria concentration in an indoor environment. Another increase of 
health risks occurs when the pathogen bacteria or their by-products are 
suspended and successfully air-borne towards the breathing zone of the 
indoor environment. Legionnaire's disease, some pneumonia and tuberculosis 
are infectious diseases caused by airborne bacteria. Bacteria can also 
cause hypersensitivity pneumonitis such as humidifier fever. Except in the 
case where a building exhibits serious water leaks, the main source of 
bacteria in a building comes from human occupation. Bacteria concentration 
of 1000 CFU/m.sup.3 (Colony Forming Unit per cubic meter) in houses and up 
to 20,000 CFU/m.sup.3 in kindergartens have been reported. 
Endotoxins are structural components of a bacteria cell wall. More 
precisely, they are lipopolysaccharides produced by gram-negative bacteria 
that are released after bacterial death. Dangerous levels of airborne 
endotoxins have been reported in numerous work environments, including 
offices and laboratories. They can cause fever and malaise, changes in 
white blood cell counts, and respiratory and gastrointestinal problems. 
Fungi exist in over 100 000 known species. Microscopic fungi include yeasts 
and molds. Most fungi produce spores (structures whose role is 
propagation) that are carried by the air. The diameter of these spores 
varies from approximately 1 to 60 microns (10.sup.-6 meters). Most 
substances containing carbon, abundant in indoor and outdoor environments, 
can serve as nutrients for molds. Accumulation of humidity in the indoor 
environment is the most important factor to be controlled to limit fungal 
growth. 
Some fungi can invade individuals and cause infectious diseases. However, 
several molds produce proteins or glycoproteins that are highly antigenic 
i.e. capable of triggering an immune response and can cause, as reactions, 
hypersensitivity diseases or allergies in susceptible individuals. These 
allergy reactions include rhinitis, allergic asthma and extrinsic allergic 
alveolitis. Growing molds may also produce several volatile organic 
compounds. These volatile compounds cause the characteristic moldy odour, 
among other things. 
Protozoa are microscopic, single cell organisms. There are thousands of 
species of protozoa varying in size, structure, morphology and physiologic 
characteristics, most of them harmless. Some are used in biotechnology and 
others are capable of causing diseases in plants and animals. These 
organisms are found in humidifiers and air filters, water treatment 
plants, thermal effluents, cooling systems, etc. A study has shown that 
humidifier fever in office workers was probably caused by antigens from 
Naegleria aerosolized by a humidifier (American Conference of Governmental 
Industrial Hygienists ACGIH, (1989)). 
Viruses vary in size from 20 to 400 nm. Airborne viruses are generally 
transmitted from person to person by droplets or projection such as 
sneezing or coughing. 
Antigens are organic substances capable of triggering an immune response In 
humans. Practically all living organisms contain proteins, glycoproteins 
or polysaccharides with antigenic potential. This is a reason why several 
microorganisms (bacteria, fungi, protozoa, acarids, etc.) have an impact 
on health via the action of antigens on the immune system. Of all the 
hypersensitivity diseases, only hypersensitivity pneumonitis, allergic 
asthma, allergic rhinitis and allergic aspergillosis are known as being a 
result of exposure to airborne antigens. The cause-effect relationship for 
microbial allergens is well known, but the complete characterization of 
the dose-response relationship is not. 
Water reservoirs are good growth media for some bacteria, fungi and 
protozoa. Consequently, ventilation system components, particularly some 
types of humidifiers, can aerosolize droplets from water reservoirs and 
therefore are of special interest due to the production of small antigenic 
particles (smaller than 2-3 microns). Epidemics of hypersensitivity 
pneumonitis have occurred in individuals when building humidification 
systems were contaminated. 
In residences, the most important sources of antigens relating to human 
health are mites, cats, cockroaches, and molds. All these organisms carry 
antigens, which can cause allergic asthma and allergic rhinitis. Dust 
mites (acarids) and their droppings that have accumulated in bedding, 
furniture or in places where the relative humidity and temperature are 
favourable, also produce antigens. 
INDOOR AIR QUALITY PROBLEM 
It is now of common knowledge that the energy efficient designs of the 
1970's resulted in tighter building envelopes with improved insulation and 
low energy consuming ventilation, without operable windows. Under these 
conditions, indoor pollutants are not sufficiently diluted with fresh air. 
Furthermore, the number of indoor air pollutant sources generally 
increases over the years. Indeed, new building materials, products and 
furnishing emit a significant number of potentially hazardous chemicals 
into the air. The resulting situation is an increase in contaminants 
circulating through the indoor environment, with insufficient outside air 
introduced to dilute the contaminants. 
Indoor air quality (IAQ) is a complex issue, much more so than any single 
environmental issue. There are hundreds of pollutants that affect IAQ and 
thousands of sources of these pollutants. Research indicates that more 
than 900 different contaminants are present in conventional indoor 
environments. 
If need for comfort, health and well being are not satisfied, building 
users may begin to complain of symptoms which are associated with poor 
IAQ. 
Headaches, burning and itching eyes, respiratory difficulties, skin 
irritation, nausea, congestion, cough, sneezing and fatigue are some of 
the most common complaints. Another complaint associated with poor IAQ is 
that there is an unidentifiable smell in the indoor environment. Odours 
are often associated with a perception of poor air quality. 
An increasing percentage of the human population is becoming more sensitive 
to a number of chemicals in indoor air, which are often at very low 
concentrations. This condition, which has been identified as Multiple 
Chemical Sensitivity (MCS), is currently the object of medical research. 
According to the United States Environmental Protection Agency (EPA), the 
effects of indoor IAQ problems are often non-specific symptoms rather than 
clearly defined illnesses. Although they can be vague, the symptoms seem 
generally worse after a day in the workplace and may altogether disappear 
when the occupant leaves the building. 
Legionnaire's disease, tuberculosis and hypersensitivity pneumonitis are 
examples of building related illnesses that can have serious and even 
life-threatening consequences. 
In light of the above, the need for efficient air purification is easily 
understandable. 
BRIEF DESCRIPTION OF THE PRIOR ART 
The simplest and most common way of maintaining reasonable air quality 
standards inside a building is to dilute the indoor air with outdoor air 
through an adequate ventilation system. Not only is this method energy 
intensive but the indoor air quality will be satisfactory only if the 
outside air is not itself contaminated. Experiments have demonstrated that 
by continuously changing a portion of the air inside a conventional house 
with fresh air from outside, it is possible to maintain a level of 1000 
CFU/m.sup.3 inside the house if the air outside has a level of 500 
CFU/m.sup.3. 
In order to purify air from essentially solid particulate contaminants, 
such as dust, air purifiers using various types of air filters are 
conventionally used. Of course, when air filters are used in buildings, 
they require routine maintenance to maintain them at an optimal efficiency 
level. Filter based air purifiers can be classified as passive air 
purification devices. When filters become clogged, ventilation air flow 
drop down, which further aggravates the IAQ problem. 
One major drawback of the filter based air purifiers is that they become a 
source of new pollutants if they are not regularly cleaned. Indeed, 
bacterial growth on the filter is favoured by the concentration of organic 
dust and moisture. Most bacteria and viruses are too small to be captured 
by filters, except for very fine filters, that exhibit relatively high 
pressure drop for low air flows. 
To overcome this drawback, U.S. Pat. No. 5,330,722, issued to William PICK 
et al. on Jul. 19, 1994, suggest the use of an ultraviolet (UV) lamp to 
irradiate the filter of an air purifier to thereby expose the filter to 
germicidal levels of radiation and therefore rendering the air purifier 
consistently effective. 
Another solution of the above detailed drawback is described in U.S. Pat. 
No. 3,750.370, issued to Erhard BRAUSS et al. on Aug. 7, 1973. In this 
document, Brauss proposes the use of germicidal UV lamps in order to 
control biological contaminants by irradiating them while they are in 
suspension in the air to be treated. 
Although these methods may be effective for some biological contaminants, 
they are inoperant for molecular size non-living contaminants such as 
formaldehyde, carbon monoxide, and other commonly found indoor chemical 
compounds. 
Three general methods are currently used to purify indoor air and to render 
molecular size contaminants harmless. 
The first method consists in adsorbing the contaminants on an activated 
carbon or potassium permanganate filters. A major drawback with this 
method is the required frequent replacement of the filter. This method is 
therefore a high maintenance and expensive solution which is not well 
adapted for residential use. Furthermore, should this method gain general 
acceptance and thereby large scale commercialization, the disposal of a 
large quantity of contaminant saturated filters would create a new 
problem. 
The second method consists in the direct incineration of the contaminants 
by way of flame. Major drawbacks of this method are the high costs 
involved in the operation of a contaminant incinerator and the fact that 
the treated air cannot be recycled and must be exhausted. This method is 
therefore not suited for low contaminant concentrations or small scale 
applications. 
The third method involves oxidation by ozonation of the contaminants to 
render them harmless by contact with oxygen molecules. Indeed, the 
meta-stable molecule of ozone, which is formed of three oxygen atoms, is 
used as an oxidizer to degrade chemical compounds. This method is highly 
efficient and devices using this method have been used for a number of 
years for rapid decontamination and elimination of smoke odours in an 
environment that has undergone a fire. However, the levels of ozone 
production of these devices are dangerously high during the treatment of 
the room and must therefore be used only in unoccupied spaces. 
More specifically, the Occupational Safety and Health Association (OSHA) 
specifies, in its standard to be complied with, that the maximum ozone 
concentration in the air of an occupied room is 0.05 ppm (parts per 
million). 
As will be apparent to one of ordinary skill in the art, in order to be 
efficient, an ozone generation based air purifier needs to produce ozone 
concentration levels that are several times the maximum-level of the OSHA 
standard. 
OBJECTS OF THE INVENTION 
An object of the present invention is therefore to provide an improved air 
purifier. 
Another object of the invention is to provide an air purifier that 
simultaneously performs chemical and biological purification by ozone 
production while avoiding the drawbacks of the prior art. 
SUMMARY OF THE INVENTION 
More specifically, in accordance with the present invention, there is 
provided an air purifier comprising: 
a housing having an air inlet for receiving air and an air outlet for 
exhausting air, 
means mounted within the housing for generating mono-atomic oxygen 
downstream of the air inlet, the generated mono-atomic oxygen reacting 
with chemical contaminants present in the air and degrading the 
contaminants by successive oxidation to odorless and inoffensive 
by-products, thereby purifying air from the chemical contaminants; a 
portion of the mono-atomic oxygen generated combining with oxygen 
molecules present in the air to form residual ozone; and 
means mounted within the housing for generating low frequency photons 
downstream of the mono-atomic oxygen generating means, the low frequency 
photons killing by irradiation biological contaminants present in the air 
and degrading the residual ozone produced, thereby purifying air from the 
biological contaminants and from residual ozone. 
In a preferred embodiment of the present invention, an internal surface of 
the housing is made of UV reflective material such as aluminum. 
In another preferred embodiment, the air purifier includes a turbulence 
generator including a plurality of deflective baffles extending 
essentially perpendicular to the air inlet and oriented in such a manner 
as to generate turbulence and swirl in the air entering in the housing 
through the air inlet promoting dispersion and mixing of air received 
within the housing through the air inlet. 
In yet another preferred embodiment, the vacuum UV source includes a UV 
lamp tube emitting energetic UV photons having a wavelength in a range of 
about 170 to about 220 nanometers, and the low frequency photon generating 
means includes a germicidal UV-C lamp tube emitting UV-C photons having a 
wavelength in a range of about 220 to about 288 nanometers. 
In another embodiment of the present invention, the UV lamp tube emitting 
energetic photons and the germicidal UV-C lamp tube are embodied together 
in a ballasted dual zone mercury vapor lamp. 
The air purifier according to the present invention presents many 
advantages. For example, it allows for the destruction of more than 80%, 
preferably more than 99%, of the organisms in the treated area, lowers the 
CFU count in a room to the same degree as would be obtained by ventilating 
the room at a rate of more than 100 air changes per hour. 
Other objects, advantages and features of the present invention will become 
more apparent upon reading of the following non restrictive description of 
preferred embodiments thereof, given by way of example only with reference 
to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purpose of simplicity, the same numeral references have been used 
throughout the description and drawings to identify the same structural 
elements. 
FIGS. 1 to 3 of the appended drawings illustrate a chemical and biological 
air purifier 10 according to a first embodiment of the present invention. 
The air purifier 10 includes a housing 12, a control box 14 mounted to the 
housing 12 through posts 13a and 13b, a turbulence generator 16, a 
mono-atomic oxygen generator under the form of a vacuum UV source 18 and a 
low frequency photons (UV-C photons) generator under the form of a 
germicidal UV-C source 20. 
The housing 12 has an inlet 22 and an outlet 24, both aligned on a 
longitudinal axis 26, and a reflective inner surface 28 to reflect back 
photons emitted from the germicidal UV-C source 20. It has been found that 
a reflective inner surface made of aluminum is efficient to reflect UV 
photons. Of course, other reflective materials may be used. 
The control box 14 includes an electrical wire 30, a ballast (not shown) 
and a switch 32 to activate or deactivate both the vacuum UV source 18 and 
the germicidal UV-C source 20, and a view port 34. Many types of ballasts 
may be used depending on the type of UV sources 18 and 20 used. These 
ballasts are well known to one skilled in the art. It has been found that 
ballasts sold by ROBERTSON TRANSFORMER CO. under the part number 
ss2060-4p, ss16550 p, seghp287 p are adequate. The view port 34 is aligned 
with post 13b to enable visual confirmation of the operation of the UV 
sources 18 and 20. Of course, the post 13b is hollow and the view port 34 
is provided with adequate filters (not shown) to prevent eye damage. 
In FIGS. 1 to 3, the control box 14 has been shown mounted to the housing 
12 through the posts 13a-13b. However, the control box 14 could be 
remotely located if such is desired. Of course, if such is the case, the 
view port 34 is to be modified or eliminated. 
The turbulence generator 16 is mounted at, or downstream of, the air inlet 
22 and includes deflective baffles 36 oriented in such a manner as to 
generate turbulence in the air entering the housing 12 through the air 
inlet 22. The possible orientations of the baffles 36 to generate air 
turbulence are believed well known in the art and will not be discussed 
further herein. 
The vacuum UV source 18 is embodied together with the germicidal UV-C 
source 20 into a single ballasted dual zone mercury vapor lamp 38 
comprising an upstream portion (see 18), acting as the vacuum UV source 
and emitting photons in a wavelength range varying from 170 to 220 nm 
(nanometers or 10.sup.-9 meters) and a downstream portion (see 20), acting 
as the germicidal UV-C source and emitting photons in another wavelength 
range varying from 220 to 288 nm. It has been found that a mercury vapor 
lamp sold by LIGHT SOURCES INC.(Milford, Conn.) under the part number 
GPH457T5VH/L4P operates properly for the present purpose. 
One advantage of using a dual zone lamp embodying the vacuum UV source and 
the germicidal UV-C source is the fact that both sources will stop 
simultaneously should one source be faulty. The risk of emitting large 
amount of ozone is therefore eliminated. 
It is to be understood that more than one ballasted dual zone mercury vapor 
lamp 38 may be used. 
It is also to be noted that the dual zone mercury vapor lamp 38 could have 
any shape as long as the vacuum UV source 18 is upstream of the germicidal 
UV-C source 20. 
Accordingly, FIG. 6 of the appended drawings illustrates another embodiment 
of the present invention where the dual zone mercury vapor lamp is a 
J-shaped dual zone mercury vapor lamp 38' comprising a straight upstream 
portion 18' acting as the vacuum UV source and a U-shaped downstream 
portion 20' acting as the germicidal UV-C source. The J-shaped dual zone 
mercury vapor lamp 38', in use, accomplishes a better purification than 
the straight dual zone mercury vapor lamp 38 of FIGS. 1-3 and is more 
compact than the straight dual zone mercury vapor lamp 38, thereby 
reducing the overall size of the housing 12 and thus the size of the air 
purifier 10. Indeed, it has been calculated that, for bacteria having a 
lethal dose of 10,000 erg/cm.sup.2, the killing efficiency is increased by 
about 6% while it is increased by about 17% for bacteria having a lethal 
dose of 100,000 erg/cm.sup.2. These efficiency increases arise from the 
fact that the mean distance between any point in the housing and the 
J-tube is decreased, therefore increasing the mean exposure level. 
Similarly, the use of an housing having an elliptical cross-sectional 
profile (not shown) would increase the killing efficiency by about 1.4% 
for the same reasons described above. 
Returning to FIGS. 1-3, the dual zone mercury vapor lamp tube 38 is 
connected to the ballast via electrical wiring 40 and socket 42. The dual 
zone mercury vapor lamp tube 38 is mounted to the housing 12 through 
clamps 44a, 44b and supports 46a, 46b. 
A probe 48, connected to a vacuum switch (not shown), for example, the one 
sold by MICROPNEUMATIC LOGIC (Ft. Lauderdale Fla.), can also be mounted 
inside the housing 12 for detecting air circulation. The probe 48 detects 
differences of air pressure between the inside and the outside of the 
housing 12 and upon detecting such differences of pressure, sends a signal 
to the vacuum switch to activate or deactivate the dual zone mercury vapor 
lamp tube 38. 
It is worth mentioning that the housing 12 of the air purifier 10 could be 
replaced by a film, adhesive on one side and photon reflective on another 
side, with which an inner portion of a ventilation duct could be 
wallpapered (not shown). Then, the electrical wiring 40 and the probe 48 
would have to be inserted through the ventilation duct. The electrical 
wires 40 would only need to be connected to the dual zone mercury vapor 
lamp 38 which would be inserted in the duct and mounted therein. 
The photons emitted from the vacuum UV source 18 are efficient to produce 
mono-atomic oxygen at the proximity of the surface of that UV source 18. 
The turbulence generator 16 contributes to diffuse the mono-atomic oxygen 
formed on the surface of the vacuum UV source 18, increasing the 
probability of an "encounter" between the mono-atomic oxygen and a 
chemical contaminant, present in the air introduced in the housing 12 and 
react with this contaminant. If it is not the case the mono-atomic oxygen 
will react with an oxygen molecule to produce an ozone molecule. Thereby 
the chemical purification efficiency is increased and the production of 
residual ozone from the reaction between mono-atomic oxygen with molecular 
oxygen is decreased. Accordingly, it is greatly advantageous to generate 
turbulence in the air entering the housing 12. 
As will be apparent to one of ordinary skill in the art, the turbulence 
generator 16 could be replaced by other devices for causing turbulence, 
for example, by a motor-driven fan to cause turbulence in the air in the 
vicinity of the vacuum UV source 18. 
The operation of the air purifier 10 will now be described. Upon activation 
of the switch 32, the air purifier 10 enters a standby mode and waits for 
a signal from the probe 48 detecting air circulation. Upon circulation 
detection, the probe 48 signals to the vacuum switch that air is 
circulating in the proximity of the housing which then activates the 
ballasted dual zone mercury vapor lamp 38. 
The air entering the housing 12 through the air inlet 22 is transformed in 
a turbulent flow by the turbulence generator 16. This turbulent flow of 
air increases the diffusion rate of the mono-atomic oxygen generated by 
the vacuum UV source 18 near its surface. The oxidation of chemical 
contaminants is almost instantaneous. 
Excess mono-atomic oxygen can produce ozone, which is a harmful gas, as a 
by-product of this process. Indeed, the combination of mono-atomic oxygen 
with molecular oxygen produces ozone. 
However, the germicidal UV-C source 20 of lower frequency, produces UV-C 
photons, preferably of a wavelength of 254 nm, with a proper specific 
energy (about 27 kJ/mol) to decompose this residual ozone into regular 
molecular oxygen. The UV-C photons emitted, producing UV radiation, are 
confined by the reflective inner surface 28 of the housing 12 instead of 
being absorbed and lost. Preferably, the reflective inner surface 28 has a 
coefficient of reflection of at least 60% for UV-C wavelengths. The 
reflection of the photons ensures a high efficiency or quantum yield of 
the UV-C photons. The UV-C photons are emitted by a UV-C zone which is 
also a powerful germicide that kills living cells such as fungi, viruses 
and spores by irradiation. Accordingly, the biological contaminants 
receive a lethal dose of UV-C radiation, that inhibits their reproduction 
by modifying their DNA. 
At a reaction level, at least three steps take place: a first activation 
phase, a reaction phase and a neutralization and germicidal phase. 
The activation phase is characterized by the production of mono-atomic 
oxygen. Energetic UV photons emitted from the high intensity UV source 18, 
preferably in the wavelength range from 170 to 220 nm, break down some 
oxygen molecules into activated mono-atomic oxygen. The quantum yield, or 
the efficiency of this action is a function of the wavelength and 
intensity of the UV source. For example, a vacuum UV source of about 8 
.mu.W/cm.sup.2 at 1 m has been found adequate. 
The reaction phase is characterized by the oxidation of chemical 
contaminants. Activated mono-atomic oxygen are mixed with the air stream 
to be treated and reacts with chemical compounds contained therein, 
degrading it by successive oxidation to odorless and inoffensive 
by-products. If chemical contaminants are outnumbered by the activated 
mono-atomic oxygen, ozone will be formed as a by-product, which is a 
consequence of the further oxidization of regular molecular oxygen. 
The neutralization and germicidal phase is characterized by the degradation 
of residual ozone formed and by the biological purification of the air. 
The lower intensity UV photons emitted by the germicidal UV-C source 20, 
preferably in the wavelength range from 220 to 288 nm, are used to 
neutralize the excess ozone generated in the reaction phase, by 
decomposing the excess ozone into regular molecular oxygen. A UV 
wavelength of 254 nm is preferred for the neutralization and germicidal 
phase. The 254 nm wavelength is well known in the art for its very high 
germicidal performance. In fact, the germicidal effect of sunlight was 
first discovered in England in 1877 by Downes and Blunt. Since their 
pioneer work, the effect of UV radiation on bacteria has been studied in 
detail and the relation between lethal action and wavelength is well 
known. The relationship between the germicidal effect and wavelength has a 
maximum effectiveness around 260 nm. and falls to a minimum at 320 nm. In 
a general way, this relationship is similar to the absorption curve for a 
nucleic acid (DNA) which is the basis of living organisms. Within the 
limits of experimental accuracy, the lethal action appears to be 
independent of the nature of bacteria to be killed. A UV-C source of about 
70 .mu.W/cm.sup.2 at 1 m has been found adequate for this purpose. 
Since 90% of the energy spectrum emitted by the germicidal UV-C source is 
concentrated at 253.7 nm by the use of the low pressure mercury vapor 
lamp, the germicidal relative effectiveness is close to 100%. 
When bacteria are subjected to any lethal agent such as heat, 
disinfectants, x-rays or ultraviolet, they do not all die at once. A 
constant fraction of the bacteria present die with each increment of time. 
A fraction of the bacteria initially present which survives at any given 
time is called a survival ratio. A fraction killed is 1 minus the survival 
ratio. Quantities are expressed as a percent by multiplying by 100. 
The killing rate is an exponential function of the time of exposure and the 
intensity of the ultraviolet radiation according to the equation: 
##EQU1## 
Where N.sub.o is the number of bacteria initially present, N is the number 
of bacteria surviving at a time t of exposure to the ultraviolet photons, 
k is a lethal dose related constant depending upon the nature of the 
organism and I is the radiation intensity. 
The radiation dose, defined as the product of I by t, required for 
(k.times.I.times.t) to equal 1 has been defined as a "lethe" and 
corresponds to a kill rate of 63.2%. A given dose results in a given 
survival ratio, regardless of whether the exposure consists of low 
intensity for a long time, or high intensity for a corresponding shorter 
time. 
The temperature has little, if any, effect on the germicidal performance of 
UV radiation between 5 degrees and 37 degrees Celsius. 
Different germicidal UV doses required for 90% killing rate of different 
biological contaminants are listed in table 3. 
TABLE 3 
______________________________________ 
Energy required 
Biological contaminant 
Ergs/cm.sup.2 
______________________________________ 
Bacillus anthracis 45200 
B. megatherium sp. (veg.) 
44400 
B. megatherium sp. (spores) 
27300 
B. paratyphosus (avererage of 3 strains) 
32000 
B. subtilis (mixed) 71000 
B. subtilis (spores) 120000 
Corynebacterium diphtheriae 
33700 
Dysentery facilli (average of 5 strains) 
22000 
Eberthella typhosa 21400 
Escherichia coli 30000 
Micrococcus candidus 60500 
M. piltonensis 81000 
Neisseria catarrhalis 
44000 
Phytomonas tumefaciens 
44000 
Proteus vulgaris 26400 
Pseudomonas aerugenosa 
55000 
Ps. fluorescens 35000 
Salmonella enteritidis 
40000 
S. typhimurium (average of 3 strains) 
80000 
Serratia marcescens 24200 
22000 
Shigilla paradysenteriae 
16800 
Spirillum rubsum 44000 
Staphylococcus 44400 
33000 
18400 
Staphylococcus aureus 
21800 
26000 
49500 
Streptococcus hemolyticus 
21600 
Streptococcus lactis 61500 
Streptococcus viridans 
20000 
______________________________________ 
The differences in sensitivity between different kinds of biological 
contaminants are not great, provided that the organisms are not of the 
spore-forming variety. It can be seen from table 3 that the spore-forming 
contaminants are much more resistant than non-spore forming contaminants. 
By way of example, B. subtilis, which is a spore-forming contaminant is 
about 5 to 10 times more resistant than E. coli. Furthermore, molds and 
yeast are considerably more resistant than bacteria, but the resistance of 
many viruses is comparable with that of bacteria. By degenerating DNA and 
nucleoprotein, the germicidal process prevents the multiplication of the 
contaminants. 
Experiments have shown that if radiation is confined instead of being 
absorbed and lost, the exposure time can be cut in half for the same 
killing ratio. The air purifier of the present invention accomplishes this 
by the use of the inner reflective housing having a coefficient of 
reflection of at least 60% for UV-C wavelengths. 
The germicidal capabilities of two different models of the air purifier on 
the organisms listed in table 1 are illustrated in table 4. A first model 
is designed for residential use and a second model is designed for high 
bacteria count environment such as hospitals, kindergartens, etc., i.e. it 
has more germicidal power. Table 4 gives the time required to sterilize 
the air up to 60% and 90% free of biological contaminants (based on a 
lethal dose of 10,000 ergs/cm.sup.2) 
TABLE 4 
______________________________________ 
Treated building area 
First model Second model 
(8 feet ceilings) 
60% 90% 60% 90% 
______________________________________ 
1500 feet square 
11 hrs 27 hrs 5 hrs 12 hrs 
3000 feet square 
21 hr.sup. 
53 hrs 10 hr.sup. 
25 hrs 
6000 feet square 
43 hrs 107 hrs 20 hrs 50 hrs 
______________________________________ 
As apparent from table 4, air purifiers according to the present invention 
are very efficient in purifying biological contaminants, even contaminants 
requiring a high energy level to be destroyed. 
Experiments in residential houses using the first model of air purifier of 
table 4 have demonstrated that a biological contaminant level of 100 to 
200 CFU/m.sup.3 may be kept inside when the air outside is at a level of 
500 CFU/m.sup.3. Measurement of the internal biological contamination 
level before the installation of the air purifier according to the present 
invention have revealed biological contaminant levels in the range of 600 
to 1000 CFU/m.sup.3. 
Turning now to FIGS. 4 and 5, an air purifier 100 according to a second 
embodiment of the present invention will be described. The air purifier 
100 is very similar to the air purifier 10 of FIGS. 1-3 with the major 
difference that the dual zone mercury vapor lamp tube 38 of air purifier 
10 has been replaced by two UV oxidizing mercury vapor lamp tubes 102 and 
104, acting as the vacuum UV source, and two UV-C germicidal mercury vapor 
lamp tubes 106 and 108, acting as the germicidal UV-C source. 
It is to be noted that when more than one vacuum UV source are used, each 
vacuum UV source is in an equidistant relationship with the other vacuum 
UV sources and with the housing. Each vacuum UV source thereby irradiate 
essentially an equal volume. 
As will be easily understood by one of ordianary skills in the art, an air 
purifier according to the present invention may be installed in an air 
return plenum af any existing ventilation system, air conditioning unit or 
heating system. More specifically, the in-duct version illustrated in the 
appended drawings may be installed as follows: 
for residential use: In the air return plenum just before the circulation 
fan, before the air filter 
for commercial use: In the air return plenum, between the last return duct 
and the circulation fan. 
The air purifier of the present invention may also, in some cases, be 
installed in the supply side of the system. 
Turning now to FIGS. 7 and 8 of the appended drawings, an air purifier 200 
according to a third embodiment of the present invention will be 
described. While the air purifiers illustrated in FIGS. 1 to 6 are 
designed to be used in ventilation systems, the air purifier 200 is 
autonomous, i.e. it is provided with an electric fan to create its own air 
flow. The air purifier 200 may therefore be placed on a table or mounted 
to a wall to purify the air of a room. 
As mentioned hereinabove, the air purifier 200 has a motorized fan 202 
continuously drawing air in an enclosure 204 through a grating 205 (see 
arrow 207). The drawn air is continuously supplied to a chamber 206 (see 
arrows 209) having a UV reflective coating 208 as previously described 
with respect to air purifiers 10 and 100. A J-shaped dual zone mercury 
vapor lamp 210 is provided in the chamber 206 to purify the air present 
therein. The lamp 210 is similar to lamp 38' of FIG. 6. The air is then 
exhausted through a directional grating 212 having a pivot axis 214 
allowing pivoting movements of the grating 212 to direct the exhausted and 
purified air (see arrow 211). 
It is to be noted that a non-reflective coating 216 and a deflector 218 are 
provided in the chamber 206 to prevent UV radiations leakage. Furthermore, 
the inwardly facing surface 220 of the deflector 218 is provided with a UV 
reflective coating to increase efficiency of the lamp 210. 
Optionally, the grating 205 may be removed to mount a directable conduit 
(not shown) to selectively draw air from a known contaminant source, for 
example an ashtray. 
Of course, while the above description concerns preferred embodiments of 
the present invention, these embodiments could be modified at will without 
departing from the spirit and nature of the subject invention as defined 
in the appended claims.