Fine particles directly emitted from aerosols, power plants, industries, construction activities and automobiles. Exposure to high concentration of PM causes premature mortality, respiratory disease and weakening of eyesight. Pre-existing heart or lung or asthmatic patients are very sensitive to PM as these minute particles are inhaled with every breath.

Formed by all metabolic activity and combustion activities. Elevated levels of CO2 indicate an insufficient amount of fresh air and can cause headaches, dizziness, increased blood pressure, poor concentration and nausea.

Concentration of Total Volatile Organic Compounds (TVOC) is up to ten times higher indoors than outdoors. Main sources are paints, chemical solvents, aerosol sprays, disinfectants, air fresheners, mosquito repellants, cosmetic products, etc. These compounds are carcinogenic to the human body. Health impacts include eye, nose, and throat irritation; headaches; loss of coordination; nausea; and damage to the liver, kidney, and central nervous system.

Formaldehyde (HCHO) is emitted as gas from certain solids or liquids. Concentration of HCHO is consistently higher indoors than outdoors. Sources of HCHO include furniture, paint, adhesives, aerosol sprays, chemical cleaners and disinfectants, and air fresheners.

A non-flammable gas with a penetrating odour that irritates the eyes and nose-lung air passages. Any SOx present indoors has come from outside. These gases are emitted from fossil fuel combustion, manufacture of sulphuric acid, incineration of refuse and coal burning. Exposure leads to a reduction or failure of lung function in asthmatics, tightness in the chest and frequent coughing.

A product of combustion, automobile exhaust, tobacco smoke, fossil fuel-fired electricity generating stations and indoor space heaters. NOx emissions are generally high in heavy traffic areas. Highly toxic in significant concentrations, causing serious lung damage with a delayed effect.

O3 can impair lung function and cause irritation to the respiratory tract. If exposure is high, it can cause irreversible damage to the respiratory tract and lung tissue. Indoor sources include office equipment and electronic air cleaners with negative ion generators.