BEIJING -- Local environmental officials said that 144 gas stations and nine oil depots in the capital region would be closed by the end of May because of cost or safety issues connected with air quality regulations.

There are 1,442 gas stations in Beijing, so the closure will affect nearly 10 percent of the total.

All oil depots and gas stations in Beijing have until the end of May to comply with vapor recovery rules, which are intended to guarantee air quality during the Olympics, a conference co-chaired by the environment, quality supervision and transportation bureaus was told on Thursday.

Vapor recovery is used during the refueling of gasoline storage tanks to reduce hydrocarbon emissions.

A specially designed nozzle is used at the gas pumps to collect vapors from the vehicle's gas tank and return these collected vapors to the service station's underground storage tank.

The facilities set for closure mainly belong to two giant oil firms, China National Petroleum Corporation and China Petroleum and Chemical Corporation.

Installing the equipment at some facilities might pose safety risks, while at others, especially in remote areas, cost-effectiveness was a factor, according to Feng Yuqiao, of the local environment bureau.

Equipping one facility costs 500,000 to 600,000 yuan (US$69,600 to US$83,600 ).