21.   Mix those four elements together, and you get a highly volatile psychoacoustical compound.

22.   Ozone, the major ingredient in smog, is formed as a ground-level air pollutant when volatile organic compounds and nitrogen oxides combine in sunlight.

23.   Part of this smell comes from molecules of air carrying volatile compounds that the user sniffs.

24.   Several of them have learned in recent months that their private wells have traces of volatile organic compounds exactly like those found in the sludge pits.

25.   Smog comes not only from vehicle exhaust but also from factory and power plant smokestacks and from emissions of volatile organic compounds, like fuel vapors.

26.   Some critics say focusing on stationary sources of volatile organic compounds is unfair because most of these emissions come from mobile sources like cars and trucks.

27.   Such instruments detect volatile compounds that evaporate from a solution to give an odor.

28.   The chemicals, called volatile organic compounds, generally occur in trace amounts that pose little threat to public health.

29.   The contaminants include volatile organic compounds, petroleum, oil, lubricants and polychlorinated biphenyls.

30.   The EPA focused on what are called volatile organic compounds or VOCs substances that can combine with nitrogen oxides from car exhausts and other sources to form smog.