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An air purifier or air cleaner is a device which removes contaminants from the air in a room to improve indoor air quality. These devices are commonly marketed as being beneficial to allergy sufferers and asthmatics , and at reducing or eliminating second-hand tobacco smoke .
They use fans to suck in the air, filter it, and either analyze it automatically there and then or collect and store it for later analysis in a laboratory. Active sensors use either physical or chemical methods. [8] Physical methods measure an air sample without changing it, for example, by seeing how much of a certain wavelength of light it ...
Ammonia pollution is most commonly measured by its presence in the atmosphere. It has no automatic relay system as with other pollutant measurements such as carbon dioxide; therefore, ammonia samples must be collected through other methods including filter packs, fabric denuders, satellite imaging, and rainwater analysis.
Portable room air cleaners with HEPA filters can be used if ventilation is poor or outside air has high level of PM 2.5. [122] Air filters are used to reduce the amount of dust that reaches the wet coils. [citation needed] Dust can serve as food to grow molds on the wet coils and ducts and can reduce the efficiency of the coils. [citation needed]
The tests showed that the people sniffer responded randomly to ammonia indicators, making it a very subjective instrument. [1] Despite this, the ability of the people sniffer to detect other effluents, such as smoke, helped it to remain a valuable tool during the Vietnam War. [1]
There are air pollution experts who view smog filtration tower projects with scepticism. For example, Professor Alastair Lewis , Science Director at the NCAS , has argued that static air cleaners, like the prototypes in Beijing and Delhi, cannot process enough city air, quickly enough, to make a meaningful difference to urban pollution.
In a photoionization detector, high-energy photons, typically in the vacuum ultraviolet (VUV) range, break molecules into positively charged ions. [2] As compounds enter the detector they are bombarded by high-energy UV photons and are ionized when they absorb the UV light, resulting in ejection of electrons and the formation of positively charged ions.
Besides that, CI facilitates the ability to detect the molecular ion peak, due to less extensive fragmentation. [3] Chemical ionization can also be used to identify and quantify an analyte present in a sample, by coupling chromatographic separation techniques to CI [ 3 ] such as gas chromatography (GC) , high performance liquid chromatography ...