Cooking fumes from roadside snack shops and restaurants may impart mouthwatering aromas - but in Mong Kok, they are an even bigger source of some kinds of harmful air pollution than vehicles, a new study has shown. The restaurants are releasing an alarming amount of organic particulate matter (PM), the study says, and one of its co-authors is urging the government to do more to tackle cooking-related emissions. The researcher, Professor Chan Chak-keung, said restaurants were a long-neglected source of pollution, contributing to about a third of organic particulate emissions in Mong Kok. "I expect many other areas could even be worse and would fully expect the problems to get more serious if it is not controlled," said Chan, a chemical engineering expert at the University of Science and Technology , which conducted the study. The Mong Kok study, conducted over four months in 2013, was published in the Journal of Geophysical Research: Atmospheres. It was the first time cooking emissions had been directly assessed in the city. In Mong Kok, it was found that organic matter composed about half of what is known as PM1, or particulates smaller than one micron in diameter. Further analysis of the particulates found cooking emissions - mainly from frying food or heated cooking oil - made up about 35 per cent of organic PM, going as high as 15 micrograms per cubic metre of air. That makes it about 50 per cent of the mix during lunch and dinner hours, compared to 26 per cent from vehicle emissions. When elemental carbon is accounted for, cooking-related organic particulates make up 40 per cent of PM1, compared to 60 per cent from traffic. "If the government can spend HK$11 billion to phase out [old diesel vehicles] … cooking emissions could deserve some attention, Chan said. "It's about setting priorities. The first step would be for the Environmental Protection Department to acknowledge that it's a problem." While most large restaurants have proper emissions control systems such as rooftop exhaust outlets and fume treatment systems, small and medium-sized roadside food businesses were of most concern, he said. Most released fumes with fans directly to the street. Given that such particulates can penetrate the lungs and bloodstream, Chan suggested the government set strict limits on emissions from restaurants. Chinese University environmental and public health expert Professor Wong Tsz-wai said organic aerosols such as cooking fumes also contained polycyclic aromatic hydrocarbons, which had been proven to cause cancer. Simon Wong Ka-wo, president of the Federation of Restaurants and Related Trades , said restaurants with general licences that prepared food using gas were required to have large ventilation systems but those with light refreshment licences, which use electricity, are only required to have basic systems. He added that in districts with as high a density of people, traffic and restaurants as Mong Kok, it was hard to pin pollution to a certain source. "It's not exactly clear whether emissions coming from restaurants are in excess of the EPD's air pollution standards," Wong said. He added that there was technology available on the market to help neutralise kitchen emissions, including electrostatic precipitators - but these required significant investment. "Mong Kok alone is home to 3,000 restaurants and food shops. It's no use if 300 restaurants make the investment but 2,700 don't." A spokesman for the department said there were not yet internationally established standards for defining the allowable limits of the constituents in cooking fumes coming from kitchens. He said the air pollution control ordinance provided control of air pollution and nuisance of air emissions, including emissions from restaurants. Large restaurants must also adopt effective equipment to minimise emissions and nuisance to nearby areas. "The EPD has been taking active monitoring and enforcement against restaurants causing air pollution," the spokesman said, adding that the PM level in Mong Kok was influenced by many sources in the area, and traffic was a major one. There were roughly 1,000 complaints related to cooking fume nuisances in each of the last three years, most of which did not warrant legal action, and a total of 15 prosecutions.