Environmental experts say real-time air quality updates mandated to start in 74 mainland cities on New Year's Day will leave local officials less room to manipulate data and hide the country's worsening pollution problem. They said hourly readings - already provided as a trial in a dozen cities, including Guangzhou, where they began on Friday - were a first step towards improving transparency and holding the government accountable for promises to clean up the air. Data will not only be released more frequently but will cover three more pollutants than at present, including ozone and smog-causing fine particles, and set tougher standards for the existing three pollutants - sulphur dioxide, nitrogen oxides and large particulate matter. Experts, however, warned that much more action would be necessary to reduce pollution. The reporting changes were announced on Friday by the Ministry of Environmental Protection, which said data collected from 496 monitoring sites would be available online and through smartphone apps. Experts cautioned that the tougher standards would lead to a sudden decline in the air quality ratings of many cities, as it would be harder for officials to achieve a "blue-sky day", when air is designated as good. Zhao Hualin, the ministry's director of pollution prevention, said recently that about 70 per cent of mainland cities would fail to meet the new standard for PM2.5 - microscopic airborne particles less than 2.5 microns in diameter, which can pose serious health risks because they can enter the bloodstream and lodge deep in the lungs. The Nanjing Municipal Environmental Bureau said on its official Weibo account on Friday that the city would see only about 220 blue-sky days a year under the new system, as opposed to 314 days under current standards. Greenpeace campaigner Zhou Rong said the existing air quality appraisal system requires only 12 hourly readings when calculating the daily average. The new system would require at least 20 hourly readings to get a more accurate average and prevent manipulation. "The monitoring results at any given site could vary greatly at different hours within a day, so there was a loophole for modifying readings," she said. Zhu Jianping, the ministry's deputy director of monitoring, told the Southern Weekly that some city governments had distorted readings to make their air quality appear worse so they could get pollution treatment funding from Beijing.