# Air Quality Effects on Human Health and Approaches for Its Assessment through Microfluidic Chips
## 3 Air Pollution Sources
### Indoor Air Pollution Origins and Prevention
#### Organic Compounds  
The so-called volatile organic compounds (VOC)s are organic chemicals, with a low boiling point causing them to evaporate at rather low temperatures. There are many different VOCs, with some perceived as scents or odors, such as formaldehyde, chloroform, benzene, acrolein, acetaldehyde, and other gases emitted from certain solids and liquids. Similar to the case of radon gas, the indoor concentration of VOCs usually exceeds the outside ones several times. There are many household products emitting VOCs. Furniture wood, many paints, and adhesives release formaldehyde (H\({}_{2}\)CO). An increase in temperature and a relatively high humidity can speed up the vaporization of formaldehyde from wood-based materials [52]. Overheated cooking oil emits not only formaldehyde, but also acrolein. Formaldehyde affects the mucous membrane, causing discomfort [52].  
Benzene (C\({}_{6}\)H\({}_{6}\)) is a cancerogenic VOC, emitted mostly by tobacco smoke, from car exhausts or stored fuels. It is a additive for gasoline (petrol), supplemented by up to 1%, thereby increasing the octane rating and reducing knocking.  
Benzene is heavier than air, so after evaporation, it descends towards low-lying areas near the ground. In humans, benzene is rapidly metabolized in the liver and excreted via the urinal tract [52]. Possible routes of exposure may be found in breathing contaminated air or by drinking soft drinks supplemented with plenty of benzoic acids and ascorbic acid [53].  
Chloroform (CHCl\({}_{3}\)) is classified as an extremely hazardous substance and can be released from hot chlorinated water at home. The exposure routes include inhalation, and oral or dermal absorption. Chloroform affects mainly the central nervous system (CNS) [54].  
There are many other VOCs, released even from office equipment, such as laser copiers and printers, carbonless copy paper, permanent markers, and glues or adhesives [55]. Some microbes, like bacteria and fungi (e.g., _Stachybotrys chartarum_) release volatile organic compounds (called microbial VOCs (MVOCs), or mushroom alcohol) [56], which are linked to sick building syndrome [57]. The symptoms of a smelly moldy house are similar to those of allergenic responses--running nose, watery eyes, itchiness, and rash. Introducing regulations to furniture, paints and other products manufacturers help to limit the exposure to VOCs indoors (for example by substituting organic to aqua-based paints). Also, the availability of products that emit only low concentrations of VOC is constantly increasing.  
The consumer should buy products that contain only low levels of VOCs, or none at all. Of course, proper ventilation helps to remove VOCs from indoor areas in buildings. There are even VOC sensors in ventilation systems, helping to increase ventilation speed, depending on the VOC concentration in the air. Some conditioning systems are designed to absorb and eliminate VOCs from the room. Interestingly, some cancer types can be detected by measuring the emitted VOCs (hundreds of different compounds) from the lungs [58].