Carbon dioxide or CO2 is a chemical compound found in air which is a molecule of one carbon and two oxygen atoms. It is found in gaseous state in room temperature and found in 0.04%(410 ppm) by volume in air. This level has increased from 280 ppm which was pre-industrialization period level. It is one of the prominent greenhouse gas, one that is responsible for capturing heat in the lower level atmosphere resulting in global warming.
According to EPA, US, CO2 enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and wood products, and also as a result of certain chemical reactions (e.g., manufacture of cement).
Higher outdoor CO2 concentrations can be found near vehicle traffic areas, industry and sources of combustion. Gasoline contains carbon and hydrogen atoms hence, during combustion, the carbon (C) from the fuel combines with oxygen (O2) from the air to produce carbon dioxide. Burning 1 litre of fuel produces approximately 2.3 kg of CO2. Which means that on an average a vehicle, which burns 2000 litres of fuel every year, releases about 4600 kg of CO2 into the atmosphere.
CO2 as a IAQ problem
Though CO2 is a natural and harmless gas, but its high concentration in the air that we breathe can be dangerous to the health. Indoor CO2 levels are acceptable up to around 1000ppm and it should not go above 1500ppm. Carbon Dioxide levels can increase inside a closed spaces given to a combination of factors that include
- Letting in outdoor air with high CO2 levels,
- Respiration taking place indoors, and
- Ventilation of the building.
An average adult’s breath contains about 35,000 to 50,000 ppm of CO2 which could be much higher than even outdoor levels. Without adequate ventilation to dilute and remove the CO2 being continuously generated by the occupants, CO2 can accumulate. As buildings and homes become more energy efficient and airtight most of the ventilation systems used today simply recycles the air to conserve energy, essentially moving the contaminated air around rather than cycling in fresh air. This results in high CO2 concentrations and poor Indoor Air Quality.
However, according to American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), CO2 concentrations commonly found in buildings is not a direct health risk alone, but it can be used as an indicator of occupant odors (odorous bio-effluents) and occupant acceptance of these odors. At the activity levels found in typical office buildings, steady-state CO2 concentrations of about 700 ppm above outdoor air levels indicate an outdoor air ventilation rate of about 7.5 L/s/person (15 cfm/person)
