11.   Smog is produced when nitogen oxides and hyrdocarbons react with sunlight to produce ozone.

12.   Some of these kinds of compounds, measured in grams per liter, react with other elements in the air to produce ozone, a component of smog.

13.   Sunlight reacts with hydrocarbons and carbon monoxide emitted by automobiles and industries to produce ozone.

14.   Sunlight reacts with hydrocarbons and carbon monoxide from automobiles and industries to produce ozone.

15.   Sunlight reacts with hydrocarbons and nitrogen oxides emitted by automobiles and industries to produce ozone.

16.   Sunlight reacts with clouds of hydrocarbons and carbon monoxide emitted by automobiles and industries to produce ozone.

17.   The state oil monopoly, Pemex, revealed that since December it had been providing Mexico City with gasoline formulated to produce less ozone.

18.   The steamy temperatures, intense sun and still winds that are normal for August are the perfect conditions for producing ozone.

19.   Ozone is produced when pollutants from cars, factories and power plants combine with sunlight and high summer temperatures.

20.   Sunlight combines with heat and pollutants from automobiles, factories and power plants to produce ozone, a pungent gas that inflames lungs and breathing passages.