Scientists have previously analyzed lab-prepared urban grime, as well as samples collected from cities, but still don't have a complete understanding of what's in the material
Researchers have found that ordinary conversation creates a conical 'jet-like' airflow that quickly carries a spray of tiny droplets from a speaker's mouth
New study provides geochemical evidence showing that forest fires expanded dramatically in the past, potentially burning up to 30 or 40 percent of global forests