Odd-even car bans might become more frequent in Beijing later this year if the capital goes ahead with proposed changes to emergency air pollution measures, according to mainland media reports yesterday. The reports came as Beijing's environmental monitors said that over half of the city's air pollutants came from neighbouring regions on heavy-smog days last year, well above previous years when the proportion was between a quarter and a third. Wang Bin, from the Beijing Municipal Bureau of Environmental Protection, said the government was considering whether to lower the bar for emergency measures, including ones that ban cars from use on alternate days depending on the last digit of their number plates, The Beijing News reported. Under existing codes, odd-even car bans are imposed when the city issues a red pollution alert - the highest on the four-tier scale. But Wang said that under the proposed changes, the ban could come into effect with an orange alert, one step down from red. The changes were expected in October at the earliest, he said. Factories should also idle 30 per cent of their output during red alerts, but Beijing has not issued a red alert since its emergency system was launched in October 2013, even when pollution readings went off the charts. Wang said the capital was learning from pollution curbs imposed during last year's Asia-Pacific Economic Cooperation meeting, when Beijing severely restricted car use for 10 days and shut down more than 4,000 factories in surrounding provinces. Renmin University professor Song Guojun said the bans inflicted huge economic losses on individuals and private businesses, and the government should consider such costs when rolling out emergency measures. But the capital has made a small gain. Beijing's average concentration of the most harmful air pollutants dropped 4 per cent last year, but it still exceeded the national safe limit by 145 per cent, the capital's environmental authorities said on Sunday. The bureau said the city's average level last year of PM2.5, the small particles of air pollutants deemed most harmful to health, was 85.9 milligrams per cubic metre - more than eight times levels recommended by the World Health Organisation. Beijing was also choked by heavy pollution on 45 days last year, 13 fewer than in 2013. The city is aiming for a 5 per cent cut in PM2.5 and a 6 per cent fall in sulphur dioxide and other pollutants by the end of this year.