Volatile Organic Compounds VOC
Due to the high abundant use of VOC-containing products indoors and the high vapor pressure of Volatile Organic Compounds, these Compounds can easily off-gas into the environment. They also occur in and are released from most common indoor materials from natural sources such as trees, animals, and plants as well as from synthetic sources such as petroleum derivatives. The aromatic VOC compound benzene, emitted from exhaled cigarette smoke is labeled as carcinogenic, and is ten times higher in smokers than in nonsmokers.
Good ventilation and air conditioning systems are helpful at reducing Volatile Organic Compound emissions in the indoor environment.
Studies also show that relative leukemia and lymphoma can increase through prolonged exposure of VOCs in the indoor environment. According one review article, most of the non-methane Volatile Organic Compound products are produced by plants and trees in our ecological environment.
Studies have shown that individual VOC emissions by themselves are not that high in an indoor environment, but the indoor total VOC (TVOC) concentrations can be up to five times higher than the VOC outdoor levels. New buildings especially, contribute to the highest level of VOC off-gassing in an indoor environment because of the abundant new materials generating VOC particles at the same time in such a short time period.
In addition to new buildings, we also use many consumer products that emit VOC Compound, therefore the total concentration of VOC levels is much greater within the indoor environment.
Relative humidity within an indoor environment can also affect the emissions of VOCs and formaldehyde. In fact, high relative humidity and high temperature allow more vaporization of formaldehyde from wood-materials and thus, can induce symptoms of sensory irritation in the eyes.
Office equipment, such as laser printers can emit ultrafine aerosol particles, which can contribute to ozone emission in an indoor environment.
There are also some chemically active VOCs, such as styrene and limonene that can react with nitrogen oxides or with ozone to produce new oxidation products and secondary aerosols, which can cause sensory irritation symptoms.
Although ozone is beneficial in the upper atmosphere because it absorbs UV thus protecting humans, plants, and animals from exposure to dangerous solar radiation, it poses a health threat in the lower atmosphere by causing respiratory problems. In addition, indoor ozone sources also include air-freshening devices and air-purifiers as well as large copy machines.
These devices can increase indoor ozone level from 6 to 453 ppb, which can induce asthmatic symptoms or increase allergic sensitization in individuals.
Photo Ionisation Detection Instruments PID
A photoIonisation detector or PID is a type of gas detector.
Typical PID Instruments measure Volatile Organic Compound and other gases in concentrations from sub parts per billion (ppb) to 20000 parts per million (ppm). The PID Instruments are the most efficient and inexpensive type of gas detector. They are capable of giving instantaneous readings and monitoring continuously. They are widely used in military, industrial, and confined working facilities for safety.
PID Instruments are ion detectors which uses high-energy photons, typically in the ultraviolet (UV) range, to break molecules into positively charged ions. As Compound elute from the GC's column they are bombarded by high-energy photons and are Compound ionized when molecules absorb high energy UV light. UV light excites the molecules, resulting in temporary loss of electrons in the molecules and the formation of positively charged ions. The gas becomes electrically charged and the ions produce an electric current, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced, and the greater the current.
The current is amplified and displayed on an ammeter. The ions recombine after passing the detector to reform their original molecules.
As a stand alone detector Photo Ionisation Detection Instruments are broad band detectors and not selective at all as these ionize everything with an Ionisation energy less than or equal to the lamp output. A PID Instrument is highly selective when coupled with some type of chromatographic technique or a pre-treatment tube such as a Benzene specific tube. The PID will only detect components which have Ionisation energies similar to the energy of the photons the detector uses. This selectivity can be useful when analyzing mixtures in which only some of the components are of interest.
PIDs are non-destructive detectors. They do not destroy/consume the components they detect. Therefore they can be used before other detectors in multiple-detector configurations.
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