21.   Despite cleaner technology, its ozone levels have changed little since then.

22.   Elevated ozone levels can harm vegetation and animals, including humans.

23.   Engelhard also said its original estimates of air flow and ozone levels differed from actual levels and led to smaller improvements in smog reduction.

24.   He acknowledged that sun rays pass through more atmosphere in Ushuaia than in cities such as Buenos Aires or Boston, where ozone levels are far more normal.

25.   He asserted that emissions from hardwood forests would produce ozone levels above the new standard.

26.   He predicted that ozone levels may worsen for another decade before human-caused damage begins to reverse.

27.   High ozone levels also indicate the presence of other chemicals that produce ozone when they react in sunlight.

28.   If this were happening in late August, when ozone levels are at their highest, the combined effects of smoke and ozone could make the air very toxic.

29.   In Houston, high ozone levels last generally through November.

30.   In March, the state failed to meet a deadline to submit a plan to the EPA detailing how Dallas-Fort Worth would reduce ozone levels.