Query: “Carbon dioxide hurts nobody’s health.

Relevant passages:
Smog <=SEP=> Smog is a type of air pollutant . The word `` smog '' was coined in the early 20th century as a portmanteau of the words smoke and fog to refer to smoky fog , its opacity , and odour . The word was then intended to refer to what was sometimes known as pea soup fog , a familiar and serious problem in London from the 19th century to the mid 20th century . This kind of visible air pollution is composed of nitrogen oxides , sulfur oxides , ozone , smoke or particulates among others ( less visible pollutants include carbon monoxide , CFCs and radioactive sources ) . Human-made smog is derived from coal emissions , vehicular emissions , industrial emissions , forest and agricultural fires and photochemical reactions of these emissions .   Modern smog , as found for example in Los Angeles , is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog . In certain other cities , such as Delhi , smog severity is often aggravated by stubble burning in neighboring agricultural areas . The atmospheric pollution levels of Los Angeles , Beijing , Delhi , Mexico City , Tehran and other cities are increased by inversion that traps pollution close to the ground . It is usually highly toxic to humans and can cause severe sickness , shortened life or death .

Carbon dioxide <=SEP=> Carbon dioxide ( chemical formula ) is a colorless gas with a density about 60 % higher than that of air ( 1.225 g/L ) that is odorless at normally encountered concentrations . Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms . It occurs naturally in Earth 's atmosphere as a trace gas at a concentration of about 0.04 percent ( 400 ppm ) by volume . Natural sources include volcanoes , hot springs and geysers , and it is freed from carbonate rocks by dissolution in water and acids . Because carbon dioxide is soluble in water , it occurs naturally in groundwater , rivers and lakes , ice caps , glaciers and seawater . It is present in deposits of petroleum and natural gas .   As the source of available carbon in the carbon cycle , atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth 's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena . Plants , algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water , with oxygen produced as a waste product .   Carbon dioxide is produced by all aerobic organisms when they metabolize carbohydrates and lipids to produce energy by respiration . It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals , including humans . Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread , beer and winemaking . It is produced by combustion of wood and other organic materials and fossil fuels such as coal , peat , petroleum and natural gas .   It is a versatile industrial material , used , for example , as an inert gas in welding and fire extinguishers , as a pressurizing gas in air guns and oil recovery , as a chemical feedstock and in liquid form as a solvent in decaffeination of coffee and supercritical drying . It is added to drinking water and carbonated beverages including beer and sparkling wine to add effervescence . The frozen solid form of , known as `` dry ice '' is used as a refrigerant and as an abrasive in dry-ice blasting .   Carbon dioxide is the most significant long-lived greenhouse gas in Earth 's atmosphere . Since the Industrial Revolution anthropogenic emissions - primarily from use of fossil fuels and deforestation - have rapidly increased its concentration in the atmosphere , leading to global warming . Carbon dioxide also causes ocean acidification because it dissolves in water to form carbonic acid .