5.7 URBAN AIR POLLUTION

Major Chemical Pollutants in Photochemical Smog: Sources and Environmental Effects

Toxic Chemical Sources Environmental Effects

Tropospheric Ozone (O3) (ground-level ozone)

-formed as a by-product of photochemical smog- sometimes results from stratospheric ozone moving into troposphere (intrusion)

- eye and respiratory irritation - decreased agricultural yields - slows plant growth - deteriorates plastics and rubber - “sharp” odor

Volatile Organic Compounds (VOC’s)

- evaporation of fuels and solvents - incomplete combustion of fossil fuels - naturally occurring compounds like monoterpenes and sesquiterepnes from trees

- respiratory and eye irritation - some are carcinogenic - decreased visibility due to blue-brown haze (Blue Ridge Mountains)

Nitrogen Oxides commonly called NOx as there are many possible combinations such as NO and NO2, N2O2 etc.

- combustion of fossil fuels eg. oil, coal, gas in both automobiles and industry - bacterial action in soil (see nitrogen cycle Topic 2.2.3)- forest fires - volcanic action - lightning

- decreased visibility due to yellowish color of NO2 - NO2 contributes to heart and lung problems - NO2 can suppress plant growth - decreased immune response - may increase risk of cancer

Peroxyacetyl Nitrates (PAN’s)

- formed by the reaction of NO2 with VOCs (can be formed naturally in some environments)

- eyes, nose and throat irritation - high toxicity to plants - respiratory irritation - damage to proteins