An Overview of Air Pollutants

Air pollution is no longer a new topic since most of us have recently experienced hazy weather in different cities in China, and more and more people have been reported to get respiratory diseases due to the exposure to polluted air. The composition of the air we breathe in everyday now is not only nitrogen, oxygen and other noble gases but also include other intruders such as small particles, dust, air-borne microorganisms and so forth. The invasion of these substances undermines air quality and causes negative health impacts to humans. To better understand how air pollutants harm our health, we should first acquire the knowledge on what they are and where they come from.

Based on their characteristics, air pollutants can be classified into two categories: chemical pollutants and biological pollutants.

Chemical pollutants

Chemical pollutants are the non-living pollutants such as gases and particles that come from combustion appliances, tobacco smoke, various personal products and building materials. Their chemical compositions and forms are diverse, and their sources are multifarious. The followings are the details of most chemical pollutants we often encounter in our daily lives.


The most commonly heard pollutant nowadays would be PM2.5, or particulate matters whose diameters are less than 2.5 micrometers. To better understand its size, the diameter of our hair is about 50 to 70um, which is about 30 times bigger than PM2.5. The composition of PM2.5 mainly includes organic matters, nitrates, sulfate and crustal elements. The sources of these tiny particulates could be natural and anthropogenic. Natural sources include the ash and cinders from erupting volcanoes and forest fire, pollen, dust, and fungal spores. Anthropogenic sources include the combustion of fossil fuels (natural gas, oil and coal), burning of trash, fugitive construction and industrial dust, road dust, and kitchen smoke and so on. Except natural and anthropogenic sources, some gases in the atmosphere or those that are emitted from automobiles can react with each other and transform to PM2.5. For example, SO2+H2O →H2SO4、H2SO4+NaCl→HCl +Na2SO4、HNO3+NH3→NH4NO3, which is a type of tiny particulate matter.

A direct health effect of breathing in PM2.5 is causing pressure to our lungs and hearts, resulting with respiratory diseases. More seriously, though the sizes of those particles are very tiny, they have large surface areas and thus a lot of bacteria, germs and virus can attach onto them and take a free ride entering our body during inhalation. It is hard to imagine what those unknown invaders would do to us after entering our body!


VOCs, or volatile organic compounds that mainly include benzene and formaldehyde, are existing in a lot of stuffs in our daily life, ranging from the clothes we wear (e.g. some use DMUG to finalize designs) and the food we eat (e.g. preservative materials). More importantly, a high level of free VOCs is released from the materials we used in house decoration, mainly are:

  • The glues and adhesive that are used to make artificial boards, fiberboards and plywood

  • The coating materials used on the furniture

  • The painting materials used on the walls

Even though there are some so-called environmental friendly decoration materials in the market, it doesn’t mean that they do not contain VOCs especially formaldehyde; rather, they may set a standard for maximum amount of chemicals released only. Generally, when a house is newly decorated, there is more than 200 to 300kg formaldehyde existing in the materials used, and the release of formaldehyde lasts for 10 to 15 years after the decoration. Although we sometimes might not be able to smell it, the amount still exceeds a safe level, for people are not able to smell formaldehyde when it is 2~3 times higher than the safe level, and there are some other odors in the air which cover the smell.

The release of formaldehyde is limited when temperature is under 19℃. However, when the temperature exceeds 19℃, each increase of 1℃will make the releasing rate 4 times faster.

Research has found that formaldehyde released from newly decorated house is the main cause of leukemia. Among all of the leukemia patients who visited Beijing Children Hospital, more than 90% were found that their houses were newly decorated. It is urgent and necessary that certain treatments should be done to stop formaldehyde from doing harm to human health.

Radon, Combustion Gases, Kitchen Fumes, Tobacco Smoke and Others

Similar to VOCs, radon is a chemical that can be released from building materials such as cement, gypsum and granite. It is a chemically stable gas under normal conditions but has a property of highly radioactive, and it can destroy respiratory system after getting in human body and lead to lung cancer.

Other gases like carbon monoxide could be produced in the combustion process of fossil fuels such as coal that is used to generate heat in winter, as well as some particulate matters and other harmful gases like sulfur dioxide and nitrogen dioxide. Another common source of pollutants in a family could be the kitchen – fumes that are generated from our cooking oils also contain some cautious materials. Besides, cigarette smoking produces nicotine, polycyclic aromatic hydrocarbon, fluoride and many other pollutants that lead to cancers, especially lung cancer. Except all of these, most of other daily activities more or less will contribute to the pollutants floating in the air, such as pet dander, insecticide, and the carbon dioxide we breathe out now!

Biological pollutants

Except non-living chemical pollutants, there are also some living organisms existing in the air. For example, mould, which is a soft green or gray substance, usually forms on the furniture and walls in damp environment. The occurrence of moulds can influence air quality because mycelia fragments and spores are dispersed into the air and thus could be inhaled and affect health. Also, in the environment where there is excessive moisture, no enough ventilation or periodic disinfection, the breeding of bacteria would take place. Additionally, the existence of dust mites would be harmful to human health too. Mites, which are insect-like organisms, can bite animals and humans resulting with significant skin irritation and intense itching. Though they are tiny and invisible to our naked eyes, they make the best of other organic pollutants such as flakes of human skin and significantly contribute to asthma and allergic reactions worldwide.

To conclude, with the pervasiveness of chemical and biological air pollutants threatening to our health, it is urgent and crucial that related actions should be taken to protect ourselves and purify our indoor air environment.

Tips to Cope With Indoor Air Pollution

Having realized that the air quality is getting worse day by day, most people have started to take precautions to protect themselves from being affected by disastrous air pollutants. The utilization of air purifiers seems to be most effective way to purify the indoor air, which could be understood from the phenomenon of demand exceeding supply on air purifiers several days ago when hazy days lingered. On the other hand, the investment on air purifiers, including upfront cost and the filter maintenance cost afterward, is relatively huge and thus might not be affordable for everyone. However, we all deserve a clean and healthy air environment, and there are some other inexpensive ways we could use to make that happen. The following is a summary of the wisdoms of the folk to achieve a healthier indoor air environment.

• Ensure adequate ventilation is necessary. Most of us spend about 80-90% of our time inside the house, so it is important to make sure that the indoor air is fresh and excess water vapors (especially in bathrooms) can evaporate. We tend to close all doors and windows in winter, which is indeed not good for air circulation and ventilation. For the buildings where the natural ventilation capability is low, an exhaust fan or blower is recommended to be installed. However, it is also important to restrict ventilation when the outdoor air quality is unpleasant.

• Sunlight is a terrific natural bacteria-killer. Except non-living pollutants, some living ones like bacteria and germs also exist in the air. Since sunlight is dazzling to our eyes, we usually put curtains on our windows to block its entrance to the house. In fact, the ultraviolet ray in sunlight has high penetrability and thus is able to destroy bacteria cells. Therefore, it would be a great idea to open your curtains in sunny days to let sunlight remove some parts of harmful microorganisms from the indoor air.

• If the humidity level is high in the house, it is very easy to make stuff mildew and rot, creating a fertile environment for microorganism breeding. If you do not have a dehumidifier, you could put some gypsum or other drying agents (better choose those that are recyclable) in an open container in the house to absorb exceeded moisture.

• Certain types of houseplants such as bracket plant and money plant that can effectively absorb dust and smoke, eliminating some toxic pollutants such as formaldehyde that is commonly released by cigarette smoke and adhesive used in wood furnishings.

• Air freshener sometimes could be used to remove bad odors, but most products in the market have quality limitations and trigger some side effects, so it is not recommended to use too much of these chemicals in a long run.

• Use low-emission products and do not store them in the house. Choose the paints, glues, carpets and other products that are more environmental friendly and emit less VOCs (e.g benzene and formaldehyde). Though it is impossible to find these products that are totally free of VOCs with current technology, you still have the choice on those that have relatively less impact.

• Treat VOCs before moving into a newly-decorated house. Some cheap treatments of VOCs could be done in the early stage. For example, carbon bags could be put in every corner of the house to absorb VOCs. A more expensive way (but still cheaper than using air purifiers) is the application of photocatalyst, which is a chemical that carries on a reaction similar to photosynthesis by using sunlight as a catalyst, and this reaction decomposes air to hydroxyl and reactive oxygen that have strong reducing and oxidizing properties, which can decompose organic compounds including formaldehyde to carbon dioxides and water molecules. It can also destroy cells and kill bacteria. Photocatalyst can be applied in the form of sprays. There is no hazardous byproduct generated, so this method is relatively safe.

• Keep pollutants out of the house. We might bring different types of pollutants along with our shoes unconsciously. Hence, taking off shoes and changing to indoor shoes while stepping into the house, or putting a door mat will keep parts of pollutants out.

• To some extent, clean air starts from developing a good living habit. Flushing the toilet after using, turning on the smoke exhaust ventilator while cooking, and periodically disinfecting bathrooms and kitchen will greatly improve the indoor air quality. Frequent hand washing and face cleaning, no smoking indoors, keeping house clean and dry will help to keep you away from indoor air pollution.

To conclude, there are various low-cost but effective ways that have been come up by the general public to improve the indoor air quality. Even though not everyone would purchase an air purifier or dehumidifier or other expensive products to ameliorate the polluted air, you could start from paying attention to the details in life and developing a healthy life style. Creating a green and clean indoor air environment would not be too difficult if you start taking actions right away!

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