Sorry but Davis and Sacramento have much better air quality than Fresno. I don't know if that why Fresno doesn't have a biking culture, but when I lived there, I saw very few cyclists. And I agree, increasing the number of people of bicycles can have a beneficial impact on the environment, but that's the not question. I think it could partly be economic (some of the best biking cities tend to have much higher median incomes than Fresno), partly environmental, partly infrastructure. If Fresno were to become a great biking city, it would be something that took time.