IT IS LATE AFTERNOON at the zebra crossing outside Sogo department store in Causeway Bay. Passersby stare at a man in leather shoes and grey trousers. Allen Cheung Yiu-lam, 51, appears similar to most men his age - but only from the neck down. Look higher and he seems to be wearing a gas mask, a grey contraption shaped like a pig's snout. Some bystanders whisper and laugh, others recoil and glower at him. Cheung largely ignores them, impervious to their reaction. 'I don't care what other people think of me, wearing a mask is the only way to protect myself,' he says. Cheung is apparently the first person seen wearing an anti-pollution mask in Hong Kong. 'Not wearing a mask is like gas suicide,' he says. His words ring true. Last month air pollution in Hong Kong hit its highest level in almost a year. On Friday, March 23, the roadside index in Central peaked at 150 - the highest reading since the record of 174 on March 29 last year and well above the 100 mark at which people with heart or respiratory problems are advised to stay indoors and avoid exercise. When it comes to battling the SAR's choking fumes and particulate-laden air, Cheung says there is only one solution: masks. 'Everybody uses their hands to cover their nose, it is useless and stupid. Your hand can't prevent you from inhaling the toxic fumes,' he says. Since he's taken to wearing a mask, he rarely suffers from respiratory illnesses or coughs. He's also single - is the mask deterring more than particulates and affecting his attractiveness to women? 'I never worry about that, all my friends are used to seeing me with a mask.' Cheung says his mask, designed for industrial use, filters out toxic emissions, including the three main pollutants of Hong Kong: sulphur dioxide, nitrogen oxide and carbon monoxide, as well as air-borne germs. This is the way Hong Kong citizens will be forced to dress in the future, Cheung believes. 'More and more people will have to wear a mask in order to survive.' Masks are common in cities such as Taipei and Tokyo and wouldn't rate a second glance in these places where people treat them as a clothing item or fashion accessory. Cheung has a different mask for each season. He wears a plastic grey one in summer and a trendy purple cloth variation in winter. No matter where he goes, from taking the MTR to buying vegetables in wet markets, he never forgets to wear one. This gesture is part of a lifelong environmental campaign. The Sheung Shui-born man is a co-founder of environmental group Green Power, organic farm Produce Green Foundation and the Vegetarian Society of Hong Kong. For two decades, he has been fighting for environmental protection. He treats wearing his mask as a silent campaign against pollution and hopes that by drawing attention to the problem, he can contribute to public education. But it's only in the past two years that he has taken his voiceless protest to the streets. In October 1999, he went to a hardware shop, spent $160 on an industrial mask and his life as the 'masked man' began. Now Cheung has become so used to breathing purified air that whenever he takes it off, he feels unwell. 'The air has a strong smell of gasoline,' he says. But the price of clean air is life as an 'alien'. Every day he faces ridicule and sometimes discrimination, he says. Wherever he goes, he is aware of stares - as if he is mad, has some gross disfigurement or infectious disease. 'People keep a distance from me - they are afraid that they will be infected,' he says. In the course of an average day, people avoid proximity to him in queues, passengers refuse to sit next to him on trains and, in one incident, a woman dragged her young daughter away from Cheung when she saw him on a bus. 'In the MTR compartment, when people see me, they deliberately move away from me,' he says. Today is a typical day. It is 5pm. Cheung walks to the zone where he attracts maximum attention, the MTR. As he takes an escalator down to the train, Cheung meets dozens of eyes, men and women, young and old, locals and expatriates. A moment later, he is sitting inside a compartment, trying to look unconcerned, while the old man next to him stares curiously, covering his mouth and laughing. Giggles can be heard from near the door. Women and men are standing, their eyes rudely fixed on him. Among them is another old man transfixed, as if Cheung's mask is the most fascinating thing he has ever seen. Does he know what it is? 'A pig's snout,' the man says, smiling. Asked if he would wear it, he shakes his head and says: 'No, it would be too much trouble.' Promoting the use of masks is clearly a difficult job. Standing in front of a pedestrian crossing, a schoolgirl is shocked as she spots Cheung. 'He is very weird,' 13-year-old Icy Chan Kei-suet says. When Cheung walks towards her, the Form 2 schoolgirl sniggers and says: 'I wouldn't be seen dead in this, it looks disgusting, like a dog muzzle.' A middle-aged tai tai walks across the road, covering her nose with a hand. When asked to comment on Hong Kong's air pollution, the woman says that her husband used to cough continuously when they lived in Causeway Bay, but after the family emigrated to Canada, his cough immediately disappeared. Is she concerned enough to wear a mask like Cheung's? Her eyes widen and she looks aghast at the idea. 'I wouldn't wear it no matter how polluted the air. It is simply too ugly,' she says, quickly walking away. So it seems that vanity, not ignorance of the effects of pollution, is the reason Hong Kongers shy away from wearing potentially life-saving masks. 'SAR people have absolutely no experience in wearing masks and so they find it a difficult habit to acquire,' says Cheung, who blames lack of education. 'The health curriculum in primary schools, for example, doesn't mention about how to protect yourself against air pollution.' Government support for the use of masks is also lacking. Few departments provide them for staff working in polluted areas. At Ladies Street, Mongkok, several hawker control officers from the Food and Environmental Hygiene Department stand casually on street corners inhaling exhaust fumes from the cars and lorries roaring by. 'I haven't thought about wearing a mask,' one officer admits. 'But if my department provided one for me free of charge, I would certainly wear it.' Cheung says that he has introduced masks to many of his 'green' friends, but they all refuse to wear them. 'I am not too disappointed - I expected that.' However, his colleague Simon Chau Sui-cheong, former chairman of the environmental group Green Power, decided to brave the stares and give it a try. 'To be honest, that mask was big and ugly, but I loved it right away,' Chau writes in his newsletter promoting environmental protection. 'It gave me a great sense of safety. Even if I'm in streets filled with poisonous air, or choking from heavy smokers around me, I don't need to fear that I am being poisoned to death . . . I am making an effort to protect myself from the torture of the environment.' At first, he wasn't used to being stared at. The associate professor of translation in the Baptist University of Hong Kong says: 'But then I returned the stares with a confident and firm gaze, as if to say, 'Poor you, having to endure this poisonous air. Quick, come and learn from me how to protect yourself'.' His mask-wearing has become the subject of jokes among his students. One says: 'Once I saw him on a bus, but didn't say hello, he looked so weird with the mask - later I told my classmates and we all had a good laugh.' But masked men like Cheung and Chau are not discouraged. Earlier this year, Cheung developed a Chinese e-shopping Web site, www.air2000. com.hk, to sell masks. He has sold more than 10 pieces, although the customers never returned to replace the filters. 'That means they stopped wearing it,' he says. He believes the public needs to be made more aware of the benefits of wearing a mask. Whenever he sees passersby making the futile gesture of covering their nose with their hand, the self-appointed 'air pollution educator' makes a hand sign. He points at the person and wags a finger, then points back at his mask and gives a thumbs-up sign. He realises that his efforts alone are not enough. 'The Government should lead the way by giving masks to civil servants working in the streets and they should introduce education about the need for masks.' The Education Department's only advice to schools during periods of high air pollution is to reduce physical exercise and outdoor activities. They have 'no plan to teach students to wear anti-pollution masks'. Meanwhile, the Environmental Protection Department argues that the air pollution index seldom exceeds a level that requires the use of masks. 'We do not consider it necessary and effective for a normal person to wear masks,' according to the department's Web site. Cheung seems alone in his battle to save Hong Kongers' lungs, and he is disheartened. Standing at a footbridge looking at the grey and hazy streets of Mongkok, Cheung sighs from behind his mask. 'Fresh air is only a beautiful dream,' he says. 'I don't know when, if ever, this dream will be realised. Now the only thing I can do to survive is to wear a mask.'