Could Tasting Blood In Saliva Be Due To Breathing In Pollution?

Occasionally I wake up with the taste of blood in my saliva. When I spit, there doesn t seem to be much blood, the spit just has a slightly pink hue. Within the past few months I ve quite smoking cigarettes, though I still use marijuana daily. I rarely drink and I eat very healthy. I live in Los Angeles and ride my bike at least ten miles a day. Could it be from breathing in the pollution?