The newly opened luxury Cordis hotel looks much like many other high-end hotels in Shanghai, with its glass-sided swimming pool, vast twin ballrooms and upscale spa. But the first Cordis hotel on mainland China boasts something that is genuinely rare in big Chinese cities: clean indoor air.

Modest occupancy rates in the megacity’s 5,000-plus hotels mean operators have been desperately competing to attract guests with cheap deals and ever more luxurious features. In a city where air pollution as measured by PM2.5s – tiny particles deemed particularly harmful to health – recently increased 9% year-on-year and now regularly exceeds capital Beijing – one luxury hotel has a new wheeze.

All the air that enters the Cordis Hongqiao is passed through two levels of filtration and continuously cleaned, while double-glazed windows remain closed to seal the fresh air inside. Pollution monitors are fitted in all 396 guest rooms and TV screens display PM2.5 levels. Air quality inside the rooms is typically around 10 times better than that outside.

A screen inside a Cordis hotel room shows the air inside is 9.7 times cleaner than that outside. Photograph: Helen Roxburgh/The Guardian

“I think people can sleep easier knowing that the air quality in their room is far superior to any other hotel, and far superior to what it is outside,” says John O’Shea, managing director of Cordis Hongqiao. Guests have so far rated the Shanghai hotel highest for satisfaction out of the Langham Group-owned brand’s 22-hotel portfolio.

While air pollution has long been on the nation’s mind, indoor air is a newer battleground. Even in very polluted cities, indoor air quality can be worse than the air outside. As well as PM2.5-heavy air entering homes and offices through open windows or poor insulation, high levels of formaldehyde, carbon dioxide and volatile organic compounds (VOCs) – gases that can be emitted by poor building materials, furniture, paints and adhesives – are an additional concern.

Indoor pollution is a very serious threat. Most people spend 90% of their time indoors and exposures remain unexamined Sieren Ernst

“Indoor pollution is a very serious problem and health threat, not just in China but worldwide,” says Sieren Ernst, founder of environmental consultancy Ethics & Environment. “Most people spend 90% of their time indoors, and the exposures that we are getting from that time remain largely unexamined.”

Public awareness in China is on the rise, though. In 2013, market research provider Euromonitor says there were 3.1m air purifiers in China, in a market worth 6.9bn renminbi (£774m). By the end of this year, sales are expected to more than double in size to 7.5m air purifiers, in a market worth nearly 16.5bn renminbi.

A growing number of employers and building managers are installing air filters in offices, while relocation companies are offering indoor air-quality assessments to top-tier expats, and Starbucks built its enormous new Shanghai Reserve Roastery to Leed Platinum standards, including air quality monitoring.

Bad air day … the sun rises over Shanghai, where PM2.5 pollution recently showed a 9% year-on-year increase. Photograph: Johannes Eisele/AFP/Getty Images

China’s only home-grown, international green building standard, Reset, is primarily focused on indoor air quality. Launched by the China-based architect Raefer Wallis, a Reset-certified space must have been within healthy limits for PM2.5 (12µg/m3), carbon dioxide (600 ppm), VOCs (400µg/m3) and other pollutants for three consecutive months, and is reassessed annually.

Meanwhile, as part of its 13th Five-Year Plan, Beijing mandated at least half of new urban buildings must be green-certified by 2020. As public interest and regulatory arguments for improving indoor air gather strength, Chinese businesses and institutions are rushing to be ahead of the curve.

“We worked with a couple of schools [on indoor air quality] in Shanghai and Beijing in 2013 and 2014,” says Tom Watson, director of engineering at environmental consulting company PureLiving, which now works with around a third of Fortune 100 companies to clean up their office air. “As soon as they made the changes it became their market differentiator, then all the other schools had to follow suit, and that’s what we’re seeing replicated now in the commercial market.

“At first this will be a point of market difference, then a necessity.”

In the city’s new Taikoo Hui complex, the air inside consultancy JLL’s 22nd-floor office is largely unaffected by the hazy skyline outside. Last year, the office was recognised as the healthiest in the Asia-Pacific region and the third healthiest in the world, meeting stringent standards from the International Well Building Institute, and introducing a customised app for staff to check real-time indoor air quality.