Currently there is a temporary problem in some areas of California, like in Sequoia National Park. There is high fire danger, so most backpacker stoves that can't be switched off are prohibited. In many areas there, you are not allowed to burn wood, anyway. I believe that they do allow Esbit, but that might change.
There is a big forest fire burning near Shaver Lake which is upwind from Sequoia, so the smoky air quality should be bad.