Chemistry Worksheets (Page 3 of 3) in pdf

Chemistry Worksheets Page 3

3-8 Describe the strategies by which reduction of urban ozone levels has been attempted.

Historically, the main strategy has been to reduce VOCs. More recently, there has been a

greater focus on reduction of NO

What difficulties have been encountered by these efforts?

The main difficulties in limiting hydrocarbons is that greater ozone is produced in down-wind

regions and where natural hydrocarbon emissions is high. In using a NO

reduction strategy,

greater ozone can form in urban areas.

Is photochemical smog strictly a localized urban problem?

No. NO is converted to other species such as HNO

slowly and can be reconverted back to NO

through HNO

photolysis. This results in regional ozone (a well as other smog components)

occurring in rural areas down-wind of urban areas.

3-9 What is meant by geographic regions that are VOC-limited? NO

-limited?

VOC-limted and NO

-limited regions refer to whether reductions in VOCs or NO

would lead to

greater ozone reduction. In many situations, it makes sense to reduce only one pollutant because

reducing VOCs in a NO

-limited situation will have little effect on ozone concentrations, or, in

the case of VOC-limted situations could even lead to an increase in ozone concentrations near

urban centers.

3-10 Describe the operation of the three-way catalyst in transforming emissions released by an

automobile engine.

The catalyst works to reduce NO to N

while improving oxidation of CO, H

, and uncombusted

hydrocarbons to CO

and H

Does the catalyst operate when the engine is cold?

No.

Why is it important for convertors that the level of sulfur in gasoline be minimized?

Sulfur degrades catalysts.

Chemistry Worksheets Page 3