In a preemptive measure, the city started fighting pollution in 2010, when all vehicles, including motorcycles, were required to have emissions tests at authorized centers, supported by random roadside tests. The exhaust test is a prerequisite to car registration and sales.

Lhasa's air remains some of the best in the world, but in the first 10 months of 2013, the city recorded "excellent" in only 94.4 percent of air quality tests. Nonetheless, clean air remains a major tourist attraction.

OXYGEN DEFICIENCY

Having clean air is one thing, but keeping it that way is quite another with rising vehicle ownership. The city is considering introduction of the China National Vehicle Pollutant Emission Standards (CNVPES) IV this year, according to Wang Junmin, deputy chief of Lhasa's environmental protection bureau.

CNVPES III is the most widely used standard in China. Only Beijing has adopted the strictest Jing V standards (equivalent to Euro V standards). Shanghai and a dozen provinces including Jiangsu, Zhejiang and Guangdong follow CNVPES IV and are considering tightening the regime this year.

New standards could cut emissions from the CNVPES III level by 30 percent to 50 percent.

Using a stricter standard in Tibet could be particularly challenging. Oxygen deficiency and low air pressure result in incomplete combustion of fuel and that means more pollutants than at lower altitude, according to Wang Junmin. Cleaner fuels adapted to local thin air are being developed.

Zhang Shengguo, a senior technician in Lhasa, echoed the need to rise to national challenges in a local way.

"Altitude sickness affects not only people but also cars," he said.Zhang works for Wanrong Investment Co., a Lhasa auto dealer.

"Power deficiency, less sensitive brakes and higher fuel consumption are common problems we see," said he.

He recalled that last summer, a Kia Carnival could not be started because incomplete combustion through oxygen deficiency caused carbon deposits in the engine.

"Our solution is simple and unique. Attach an oxygen bag to the vehicle's intake pipe and increase the oxygen content in engine," said he.