Yeah, I too wouldn't want to cycle in that level of air pollution. There's a sweet spot to hit for level of comfort & safety while cycling. I just think safety is the bigger issue, because even if the surrounding environment is comfortable and the terrain is flat and the weather is nice, if cars are making it unsafe to cycle, you're not going to cycle. And further, if we solve safety, that might actually help the environmental side of things too- less air pollution.