Have you ever seen the billowing smoke plume coming from a fire? Sometimes it looks white, sometimes gray, and sometimes almost black. And it usually smells different depending on what is burning. Smoke from fires contains a complex mixture of gases (what you smell) and aerosol particles (what you see). These gases include carbon dioxide (CO2) and methane (CH4), both of which are greenhouse gases which warm our atmosphere by absorbing light. The smoke particles visible to the naked eye can warm or cool the earth’s atmosphere depending on their chemical make-up.
Wildfires, cooking emissions from stoves, and fireplace smoke used to heat one’s home all represent different types of biomass burning. Depending on the burning conditions, the chemistry and size of the particles can change. Large flaming fires produce more sooty black particles that can absorb light and lead to warming, whereas smokier/smoldering fires produce more white organic particles, which reflect light and therefore are relatively cooling. This interaction of light with the particles is termed the direct effect of climate.
Biomass-burning particles can also affect our climate by how well they form clouds, which is called the “indirect effect.” Most clouds are white and quite reflective, leading to a reduction in light reaching the surface of the earth and offsetting the warming of our planet by greenhouse gases. This combination of direct and indirect effects is very complex and thus very difficult to understand. As a result, studying the impact of fires and biomass burning on our climate represents an area of intense scientific research.
-- Prof. Kimberly A. Prather, Scripps Professor of Atmospheric Chemistry, USD Dept. of Chemistry
-- Meagan Moore, Graduate Student, UCSD Dept. of Chemistry and Biochemistry