Reactions between smog and plant proteins could explain the mysterious increases in allergies. Exhaust fumes from traffic could be turning airborne proteins into more powerful allergens, explaining why asthma and other allergies are on the rise in urban areas. Researchers have found that the mixture of nitrogen dioxide and ozone produced by vehicles can add the chemical group nitrate to the protein molecules that account for up to 5% of the particles in our air. Medical studies have shown a link between air pollution and rising allergy rates. But scientists have not been able to pin down how one causes the other. Nitration is now a prime suspect, says, Ulrich P