Motorcyclists better hold their breath. Studies indicate that drivers of two-wheelers and their passengers are the most susceptible to air pollution. Only then come cyclists and pedestrians. WHO studies say Valley residents spend Rs 30-50 million annually treating pneumonia, bronchitis, dry cough and cold, and red eyes, all caused by minuscule dust particles in the air, especially in the dry, dusty winters. Air pollution tests indicate that traffic heavy areas like Putali Sadak, Chabalhil, Patan, and Paknajol have a high concentration of suspended particles-five times above WHO-recommended 70 micrograms per cubic metre. Tests at Putali Sadak showed 210-375 microgram per cubic metre, Patan 300-350 microgram per cubic metre, and Chahabil 280 microgram per cubic metre. While health experts say masks can, to a certain extent, prevent dust particles from entering the body, the best way to deal with the menace is by reducing traffic and closing off congested junctions every once in a while. Presently, a record 171,678 vehicles ply Kathmandu's roads everyday-30,000 more than the city's road infrastructure is designed to hold. Over 110,000 of these are motorcycles.