Health and Cellular Impacts of Air Pollutants: From Cytoprotection to Cytotoxicity

Table 1

Air pollutants. The National Ambient Air Quality Standards (NAAQSs) are set by the Environmental Protection Agency under authority of the Clean Air Act and define the maximum allowable concentrations of outdoor air pollutants in the USA. Units of NAAQS are parts per million (ppm) by volume, parts per billion (ppb-1 part in 1,000,000,000) by volume, milligrams per cubic meter of air (mg/m³), and micrograms per cubic meter of air (μg/m³). Average time refers to time for which the values of NAAQS should not be exceeded in the ambient air [14–16].

Pollutants	Main sources	NAAQS
		Level	Average time
Asbestos	Electrical and building insulation; (fiber cement)
Carbon dioxide (CO2)	Fossil fuel combustion
Carbon monoxide (CO)	Incomplete combustion, exhaust from motor vehicles, emissions from certain industrial processes (agglomeration of ore, steel, waste incineration)	35 ppm (10 mg/m^3); 9 ppm (10 mg/m^3)	1 hour; 8 hours
Chlorofluorocarbons (CFCs)	Use in consumer goods (aerosol propellants, foams, fire extinguishers, refrigerants)
Dioxins and dioxin-like compounds	Byproducts of various industrial processes
Polychlorinated dibenzo-p-dioxins (PCDDs)	Waste incineration, metal smelting and refining, chlorinated pesticides, and herbicides
Polychlorinated dibenzofurans (PCDFs)	Environmental accidents contamination, waste incineration, chlorinated pesticides, and herbicides
Polychlorinated biphenyls (PCBs)	Used as coolants and insulating fluids for transformers and capacitors, and as plasticizers in paints and cements, additives in flexible PVC coatings
Hydrogen sulfide (H2S)	Paper pulp production and oil refineries
Methane (CH4)	Coal mines exploitation, garbage landfills, livestock, gas distribution
Nitrogen dioxide (NO2)		100 ppb; 53 ppb	1 hour; Annual
Nitrogen monoxide (NO)
Nitrogen oxides (NOx)	Fossil fuel combustion, industrial processes (nitric acid production, fertilizer manufacturing, surface treatment)
Nitrous oxide (N2O)	Fossil fuel combustion, some industrial processes, motor vehicles, soils, and oceans
Ozone (O3)	Tropospheric ozone formed from reaction between UV, NOx, and VOC	0.12 ppm (235 μg/m³) 0.075 ppm (150 μg/m³)	1 hour; 8 hours
Particulate matter (PM)
PM10	Natural dust, sea salt, industrial, agriculture, and forestry activities	150 μg/m^3	24 hours
PM2.5	Fossil fuel combustion, road traffic, and other transports, agriculture, and manufacturing	35 μg/m^3; 15.0 μg/m^3	24 hours; Annual
PM0.1	Residential heating, road transport, manufacturing, agriculture, waste processing plants
Polycyclic aromatic hydrocarbons (PAHs)	Incomplete combustion of organic material (wood burning, fossil fuel combustion, etc.)
Sulfur dioxide (SO2)	Sulfur-containing fossil fuel combustion (coal, lignite, petroleum coke, heavy fuel oil, heating oil, diesel),	75 ppb	1 hour
		0.14 ppm (365 μg/m^3)	24 hours
		0.030 ppm (80 μg/m³)	Annual
Toxic metals
Antimony (Sb)	miscellaneous plastics manufacturing, petroleum products, and fabricated structural metal products, thermal power generation
Arsenic (As)	Heavy fuel oil combustion
Cadmium (Cd)	Waste incineration, heavy fuel oil, and biomass burning
Chromium (Cr)	Production of glass, cement, ferrous metallurgy, and foundries
Cobalt (Co)	Nuclear facilities, production of steel and alloys
Copper (Cu)	Combustion and waste treatment, processes of ferrous and nonferrous metallurgy
Lead (Pb)	Road transport, electric batteries production	0.15 μg/m^3	Rolling 3 Months
Mercury (Hg)	Coal and oil burning, chlorine production, incineration of household, and industrial waste
Nickel (Ni)	Heavy fuel oil combustion
Selenium (Se)	Glass production, heavy fuel oil combustion
Vanadium (V)	Oil refineries, combustion of fossil fuels
Zinc (Zn)	Coal and heavy fuel combustion, ferrous and nonferrous metallurgy, waste incineration
Volatile organic compounds (VOCs)	Road transport, industrial processes involving the use (basic and fine chemicals, metal degreasing, paint application, printing, adhesives, rubber, etc.), or not of solvents (petroleum refining, use of CFCs, production of alcoholic beverages), household products