Air Pollutants Primary air pollutants - Materials that when released pose health risks in their unmodified forms or those emitted directly from identifiable sources. Secondary air pollutants - Primary pollutants interact with one another, sunlight, or natural gases to produce new, harmful compounds

Primary Air Pollutants Five major materials released directly into the atmosphere in unmodified forms. Carbon monoxide Sulfur dioxide Nitrogen oxides Hydrocarbons Particulate matter

Carbon Monoxide Produced by burning of organic material (coal, gas, wood, trash, etc.) Automobiles biggest source (80%) Cigarette smoke another major source Toxic because binds to hemoglobin, reduces oxygen in blood Not a persistent pollutant, combines with oxygen to form CO2 Most communities now meet EPA standards, but rush hour traffic can produce high CO levels

Sulfur Dioxide Produced by burning sulfur containing fossil fuels (coal, oil) Coal-burning power plants major source Reacts in atmosphere to produce acids One of the major components of acid rain When inhaled, can be very corrosive to lung tissue London 1306 banned burning of sea coal 1952 “killer fog”: 4,000 people died in 4 weeks tied to sulfur compounds in smog

Nitrogen Oxides Produced from burning of fossil fuels Contributes to acid rain, smog Automobile engine main source New engine technology has helped reduce, but many more cars

Hydrocarbons Hydrocarbons - organic compounds with hydrogen, carbon From incomplete burning or evaporated from fuel supplies Major source is automobiles, but some from industry Contribute to smog Improvements in engine design have helped reduce

Particulates Particulates - small pieces of solid materials and liquid droplets (2.5 mm and 10 mm) Examples: ash from fires, asbestos from brakes and insulation, dust Easily noticed: e.g. smokestacks Can accumulate in lungs and interfere with the ability of lungs to exchange gases. Some particulates are known carcinogens Those working in dusty conditions at highest risk (e.g., miners)

Conti….. Respirable Suspended Particulate Matter (RSPM) PM1 having size <= 1μm: effects in alveoli PM2.5 having size <= 2.5μm: effects trachea PM10 having size <= 10μm: effects in nasal part only

Secondary Pollutants Ozone PAN (peroxy acetyl nitrate) Photochemical smog Aerosols and mists (H2SO4)

Ozone Ozone (O3) is a highly reactive gas composed of three oxygen atoms. It is both a natural and a man-made product that occurs in the Earth's upper atmosphere (the stratosphere) and lower atmosphere (the troposphere). Tropospheric ozone – what we breathe -- is formed primarily from photochemical reactions between two major classes of air pollutants, volatile organic compounds (VOC) and nitrogen oxides (NOX).

PAN Smog is caused by the interaction of some hydrocarbons and oxidants under the influence of sunlight giving rise to dangerous peroxy acetyl nitrate (PAN).

Photochemical smog Photochemical smog is a mixture of pollutants which includes particulates, nitrogen oxides, ozone, aldehydes, peroxy acetyl nitrate (PAN), unreacted hydrocarbons, etc. The smog often has a brown haze due to the presence of nitrogen dioxide. It causes painful eyes.

Aerosols and mists (H2SO4) Aerosols and mists are very fine liquid droplets that cannot be effectively removed using traditional packed scrubbers.  These droplets can be formed from gas phase hydrolysis of halogenated acids (HCl, HF, HBr), metal halides, organohalides, sulfur trioxide (SO3), and phosphorous pentoxide (P2O5). 

Emission Inventory Source Classification (1) Point sources: large, stationary sources of emissions that release pollutants in quantities above an emission threshold. For eg. Industrial processing, power plants, fuel combustion and municipal incinerators (2) Area sources: represent numerous facilities or activities that individually release small amounts of a given pollutant, but collectively release significant amounts of a pollutant. For example, dry cleaners, vehicle refinishing, gasoline dispensing facilities, and residential heating.

(3) Mobile sources (a) On-road vehicles: which include automobiles, light trucks, heavy-duty trucks, buses and motorcycles (b) Non-road vehicles: such as airplanes, trains, combustion engines on farm and construction equipment, marine engines, and lawn mowers.

(4) Biogenic or natural sources: include trees, vegetation, and other microbial activity that can make a significant contribution to total volatile organic compound (VOC) and nitrogen oxides (NOx) emissions .In the past, the impact of biogenic VOCs was not considered when ozone control strategies to limit emissions of either NOx or VOC were developed. However, the importance of biogenic VOC emissions in an ozone inventory became apparent in some regions when the biogenic VOC emission estimates were compared to anthropogenic VOC emission estimates.

References Masters, G. M., 1991. Introduction to Environmental Engineering and Science, Pub., Printice-Hall, India. USEPA, 2007. Online literature from www.epa.gov Rao, M.N. and Rao, H. V. N., 1993. Air Pollution, Tata Mc-Graw Hill, New Delhi. Murty, B. P., 2004. Environmental Meteorology, I.K. International Pvt. Ltd., New Delhi. Nevers, N.D. 2000. Air Pollution Control Engineering, Second Edition, Pub., McGraw Hill, New York. Cheremisinoff, N.P., 2002. Handbook of Air Pollution Prevention and Control, Pub., Butterworth-Heinemann, Elsevier Science, USA.