7.2 - Photochemical Smog APES

The higher the sunlight intensity, the greater production rate of _____

O2

Smog concentrations vary over time and space according to what?

environmental conditions and sunlight (the source of energy for photochemical reactions)

Examples of Volatile Organic Compounds (VOCs)

formaldehyde and gasoline

Sources of VOC's

fuel tanks, paints, cleaners, industrial processes, non road equipment

What can photochemical smog harm?

human health in several ways, including causing respiratory problems and eye irritation, lung and skin cancer, plant diseases

Where does photochemical smog often form?

in urban areas because of the large number of motor vehicles there (ex. Los Angeles - Long Beach - Riverside, Calif., Houston - Baytown - Huntsville, Texas, Dallas - Fort Worth, Texas)

The greater the wind speeds and mixing heights the lower the ________________

smog concentration

What will the direction of the wind control?

the areas where smog is transported

Photochemical smog can be reduced through what?

the reduction of nitrogen oxide and VOCs

Factors affecting photochemical reactions

- Light intensity - Hydrocarbon reactivity. - Ratio of H-C to nitric oxide - Presence of light absorbers - Meteorological variables - Height and intensity of atmospheric inversion

Photochemical smog

A mixture of pollutants that are formed when nitrogen oxides and volatile organic compounds (VOCs) react to sunlight, creating a brown haze above cities. It tends to occur more often in summer, because that is when we have the most sunlight.

Volatile Organic Compounds

-Organic compunds that evaporate readily -with sunlight, can react with nitrogen oxides to form photchemical smog

How has Los Angeles air quality dramatically improved?

-Reduced VOC's: cleaner gas, "smog" checks -Geography, VOC's, NOx still make LA smoggy

Local Topography of Photochemical Smog

-Smog is most often formed over large cities lying in valleys. -Hills or mountains surrounding these cities shelter from most of the wind and on warm, calm days severe smog can occur. (For example, Los Angeles) -The frequency and severity of photochemical smogs in an area depend on local topography, climate, population density and fossil fuel use.

Do trees fight air pollution?

-Trees actually give off VOC's themselves -Smog in Atlanta: VOC's come mostly from forests

Best step is to reduce emission of primary pollutants

-VOC reduction has little effect: excess reagent -NOx reduction more important: limiting reagent VOC + NO + O2 + sunlight -----> 03 + HNO3 + Oxidized VOC's

What time of day is Nitrogen oxide produced and why?

Early in the day, Ozone concentrations peak in the afternoon and are higher in the summer because ozone is produced by chemical reactions between oxygen and sunlight.

Primary pollutants of Photochemical Smog

Nitrogen oxides and VOCs, combine to change in sunlight in a series of chemical reactions, outlined below, to create what are known as secondary pollutants.

Secondary pollutants of Photochemical Smog

Ozone that forms at ground level. While ozone is produced naturally in the upper atmosphere, it is a dangerous substance when found at ground level. Many other hazardous substances are also formed, such as peroxyacetyl nitrate (PAN).

Solutions to Photochemical Smog

Reducing the quantities of the pollutants entering the atmosphere is the answer to how to reduce photochemical smog. Improved design of gasoline storage and dispensing systems reduces the emissions of hydrocarton VOCs. Catalytic converters reduce hydrocarbon and carbon monoxide emissions from automobiles.

Natural source of VOCs.

Trees

When do Volatile Organic Compounds evaporate or sublimate?

at room temperature

When is Photochemical smog formed?

When nitrogen oxides and volatile organic hydrocarbons react with heat and sunlight to produce a variety of pollutants.