Probably worth adjusting the title -- air quality is not just a measure of pollution. In this case, both SF and Portland are filled (unfortunately) with wildfire smoke, rather than a man-made pollutant...
As climate change was a key driver of these fires and those in Australia earlier this year, then I feel like it's perfectly reasonable to say this is man made pollution.
Coal and oil are also a "natural" fuels, but we burn those too and we say it's man made pollution.
