sunlight causes nitrogen dioxide, no2, to separate into nitric oxide, "no," and an oxygen atom. the oxygen atom adds to naturally occurring molecular oxygen, or o2, to create ozone. but this is just the first step in a chain reaction of ozone production. the remaining nitric oxide reacts with unstable molecules that are products of hydrocarbons oxidizing in the atmosphere, recreating nitrogen dioxide, causing a vicious cycle of ozone production. kolb: so ozone gets formed as a secondary pollutant. it's not emitted directly, and it's important to understand not only how much ozone is in the atmosphere, but how much of its precursor chemicals are there so we can predict what the ozone will look like as the wind blows that chemical mixture across the countryside. narrator: aerodyne's van has been deployed all over north america to help engineers and planners identify the best strategies to reduce pollutants from industries and transportation systems. kolb: we've worked with the metropolitan transit authority in new york city that runs about a third of the city's buses, to determine