51.   That means the ozone level was being cut roughly in half by the Prem-Air System.

52.   The city has also had elevated ozone levels due largely to the heat and smog from cars.

53.   The city may opt to voluntarily comply with some of those rules as a way of beginning to reduce ozone levels sooner.

54.   The company also said its original estimates of air flow and ozone levels differed from actual levels and led to the smaller improvements.

55.   The eight affected counties where ozone levels exceed federal air quality standards are Harris, Brazoria, Fort Bend, Galveston, Montgomery, Waller, Chambers and Liberty.

56.   The Fort Worth-Dallas area has struggled for decades with ozone levels that continually violate the federal health standard.

57.   The heat helped drive ozone levels above federal standards, prompting the Maricopa County Environmental Services Department to issue an ozone advisory.

58.   The governor lauded efforts made by government employees, private businesses and citizens this summer to cut ozone levels.

59.   The new EPA standard measures average ozone levels over eight hours.

60.   The ozone level is measured to determine attainment of federal air quality standards.