The whole issue of dust is big in the San Joaquin Valley. Shaking those almond trees - with a season load of dust - can throw a lot of particles into the air, plus tillage and rowcrop harvest add to it. It's all compounded out there by the fact that the valley is essentially a bowl, it doesn't rain much and then you get wind storms. There probably are some folks from the SJV who can comment on this more, but at times it's been a political hot button, maybe still is. I'm heavily involved out there about 7 months a year but don't actually live in the valley.

Here's a link to a related article:

Ag Groups Fighting EPA Dust Rule