Photochemical smog revision.

You wanted to know more about ozone…

Ozone, O3, is found throughout the atmosphere.  Ozone is a pale blue gas that is poisonous to human life and plants, even in small concentrations.  It is harmful when it occurs near ground level, but serves an essential function in the upper atmosphere because it absorbs high energy ultra violet radiation.  Without this vital protection this radiation from the sun would eventually destroy life on earth.

A youtube search has found a video by the Periodic Table of Videos.  It has quite a nice summary…


Nitrogen oxides lead to the formation of ozone in the troposphere.

And you need to be able to:

Describe and write equations showing the role of nitrogen oxides in the formation of ozone in the troposphere.

The emission of nitric oxide (NO) from engines burning fossil fuels may lead to the formation of ozone, and subsequently photochemical smog in the lower atmosphere.

Nitrogen and oxygen from the air combine in engines (which have high temperatures) to form nitric oxide (NO).

Nitric oxide is an example of a primary pollutantPrimary pollutants are emitted directly into the atmosphere from a source such as a combustion chamber in a car engine or furnace.

Once in the atmosphere, nitric oxide can be converted to nitrogen dioxide.

Nitric dioxide is an example of a secondary pollutantSecondary pollutants are formed in the atmosphere by chemical reactions of the primary pollutants.

Nitrogen dioxide is very reactive in the atmosphere. By absorbing solar radiation it undergoes photochemical dissociation into nitric oxide and atomic oxygen.

NO2 –> NO + O

The atomic oxygen formed is very reactive and then reacts with oxygen molecules to produce ozone.

O2 + O –> O3

My tip to you:

You are required to describe and write equations

  • If you cant remember the equations, this is one of those times that you are going to have to memorise them.
  • Once you have done that, I would explain those equations using words.  That will go towards the describing part.

But there’s more to it:

Nitrogen oxides and ozone in the troposphere are pollutants.

And you need to be able to:

Explain the terms ‘primary pollutants’ and ‘secondary pollutants’ with reference to the harmful effects of nitrogen oxides and ozone in the troposphere.


I have already covered the primary and secondary pollutants part above.  Next you need to be able to explain the harmful effects of those pollutants.

In short:

  • Ozone attacks the double bonds in rubber and polymers.  This causes cracking/perishing.
  • Ozone can cause health problems such as coughing, wheezing, and irritation of the respiratory system.
  • Plants suffer when exposed to ozone. Their leaves yellow, and therefore the photosynthesis rate is reduced.
  • Nitrogen dioxide causes similar effects in plants and animals.
  • Nitrogen oxides are responsible for the formation of acid rain.


It is possible to reduce the quantities of nitrogen oxides generated by cars.


With the use of catalytic converters.

Basically, the catalytic converter removes the pollutants from the car exhaust and changes them to less harmful gasses.

This is explained in more detail in the videos that I have already shown you…

Some equations that can explain what is going on chemically:

2CO + 2NO –> N2 + 2CO2

CO + H2O –> H2 + CO2

2CO + O2 –> 2CO2

2H2 + 2NO –> 2H2O + N2

Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


%d bloggers like this: