Shooting the messenger is never a good idea, especially when people's health is at stake. Yet that is what the Chinese government seems intent on doing to US diplomatic missions, which since last year have been issuing data on the smallest and most harmful air pollution particles, PM2.5, in three cities. Deputy Environment Minister Wu Xiaoqing has called for an end to the service, condemning it as a violation of national laws and diplomatic codes of conduct. His criticism is not only unreasonable but unjustified - and worse, ignores the risks posed by poor air in China's heavily polluted cities. It was those potential threats to health that prompted first the US embassy in Beijing, and then its consulates in Shanghai and Guangzhou, to fill a gap for American expatriates. Informing about PM2.5 particles, which can lodge deep in the lungs and enter the bloodstream, is common practice in developed countries, but until this year, not on the mainland or in Hong Kong. Chinese officials have collected PM2.5 data, although not released it, instead issuing information about larger PM10 particles, which makes air readings look better than they really are. In Beijing, that meant results were good or excellent 80 per cent of the time, contrasting sharply with those from the embassy showing just 20 per cent of days as acceptable. Unsurprisingly, word of the discrepancy got around and became a major topic of discussion on microblogs, embarrassing the central government and prompting it to call on cities to follow suit. There nonetheless has remained a gap in readings, explained away as being down to different standards. But whether those of the World Health Organisation are followed, as the US does, or lower ones are adhered to, the fact remains that numbers alone are not enough. Monitoring and releasing information is pointless unless measures are also taken to make the air healthier. A nation's success relies on the health of its people. Criticising the United States for highlighting a failing is a smokescreen for grievous inaction.