I live in Santa Clara county (Sunnyvale) and I'm surprised by the 'F' rating (and a bit disappointed). But, with all the ridiculous overcrowding, lack of public transit (or lack of public transit users), plus the trees and flowers that are planted here (all of which generate huge amounts of pollen), I guess I shouldn't be entirely surprised.
This year, I've been having some serious allergy problems, the likes of which I haven't seen since I was a young child. I've had a total of 4 colds/sinus infections since January, the most recent being quite severe and long-lasting with a secondary case of tonsilitis (and it's only mid-May). "Normal" for me is once or twice a year. The problem's been so bad with the chronic infections that I'm having to go the medical route and will be visiting an allergist soon to try to get a handle on what specifically is causing all the problems. Then we need to find a way to treat it.
2012 has been a horrible year for allergies - everyone's complaining. Add to it the pollution and stressful living environment (Silicon Valley Pressure Cooker) and you have a perfect recipe for chronic health problems.
Maybe I should go through with plan B and move to Santa Cruz - maybe the commute is worth it for the cleaner air (and slighly cheaper rents). The more laid-back lifestyle there might also help with the Pressure Cooker effect, too.