Westchester County officials are proposing new legislation that will hold leaf blowers to certain quality standards in an effort to reduce air pollution.Westchester County Executive Andy Spano is proposing a new law that would require landscapers to use low-emission leaf blowers. He says the legislation is essential for the health of Westchester County residents. Leaf blowers are powered by two-stroke engines, which release exhaust. Experts say using some leaf blowers for a 30-minute time period releases more exhaust into the air than a car driving 2,000 miles.The proposal will be presented to the County Board of Legislators this week. If it is passed, it will only apply to landscapers, not the general public. Contractors would be required to use leaf blowers with four-stroke engines, which are cleaner and quieter. All of their equipment would need to be converted by 2009.