We often talk of outdoor or ambient air pollution and its various ill-effects. Consequently, indoor air pollution is often ignored. Indoor pollution may be as bad as or even worse than the outdoor pollution and can be a major health hazard even in urban areas. Indoor air pollution is an equally urgent issue that needs attention because most people spend most of their life indoors — inside schools and colleges, homes or offices, commercial or industrial buildings.

Volatile organic compounds (VOCs) are a type of indoor air pollutant. They are gases that are released into the air from products or processes. Scientifically, VOCs have been defined as “organic chemical compounds whose composition makes it possible for them to evaporate under normal indoor atmospheric conditions of temperature and pressure”. Since the volatility of a compound is generally higher, its boiling point is lower, the volatility of organic compounds are sometimes defined and classified by their boiling points (EPA).

The outdoor air is an important source of indoor air pollution. Therefore, VOCs are always found in indoor air as well as in the ambient outdoor air. VOCs are the most common contaminant of indoor air.

The different types of VOCs are ethylbenzene, carbon tetrachloride, benzene, 1,1,1-trichloroethane,  xylenes, tetrachloroethylene, toluene, trichloroethylene, styrene and 1,4-dichlorobenzene.

The group of VOCs is often treated as one unit, and is termed TVOCs or total VOCs.

SVOCs or semi-VOCs are a subgroup within the VOCs. They are not as volatile as other VOCs and have a higher molecular weight and higher boiling point at which it evaporates into the air.

Another point of difference between the two is that VOCs have an aroma when released as they are typically released from household items such as air fresheners, insect repellents, cleaning products, disinfectants, cosmetics and deodorants, dry-cleaned clothing and also in new furnishings, upholstery, carpeting, woodwork and paint. Glues and adhesives, permanent markers, varnishes, photographic solutions, copiers and printers are other sources of indoor VOCs.

On the other hand, SVOCs are released from materials such as pesticides, furniture, and some cookware and hence, do not have an aroma and they adsorb to all indoor surfaces as dust. They can remain indoors for years after they are introduced, even if the original source is removed.

Petroleum products and diesel, wood burning, industrial emissions and chemical solvents are sources of outdoor VOCs.

VOCs are the main precursors to the formation of ground level ozone and particulate matter, which together form smog. The adverse effects of smog on human health and the environment are well known. VOCs combine with nitrogen oxides (NOx) in sunlight to form the ground level ozone (tropospheric), which is harmful. The higher ozone layer (stratospheric) is good as it acts as a shield and protects from harmful UV rays.

Exposure to VOCs can have short-term and long-term health effects.

Short-term exposure can cause dizziness, nausea, allergies, asthma and headache. Leaving the room or space containing the VOCs will relieve the symptoms of acute exposure.

Long-term exposure to indoor VOCs can cause sick building syndrome, in which the occupants of a building experience acute health- or comfort-related effects that seem to be linked directly to the time spent in the building. No specific illness or cause can be identified.

Some VOCs are suspected or known carcinogens. Benzene has been classified as Group 1 carcinogen i.e. confirmed as carcinogenic to humans by the International Agency for Research on Cancer (IARC). World Health Organization (WHO) guidelines on benzene say that “No specific guideline value has been developed for air. Benzene is carcinogenic to humans, and no safe level of exposure can be recommended”.

There is an urgent need to create public awareness about VOCs, their sources and harmful effect on health as a first step towards controlling and preventing exposure to this health hazard.

The Air Quality Index (AQI) does not take into consideration VOCs when calculating the air quality. But, VOCs are also major toxic air pollutants, which are also hazardous to human health, more so, because they are also present in high concentrations in the indoor environment causing prolonged exposure.

Dr KK Aggarwal

Padma Shri Awardee

President Elect Confederation of Medical Associations in Asia and Oceania (CMAAO)

Group Editor-in-Chief IJCP Publications

President Heart Care Foundation of India

Immediate Past National President IMA