Environmental & Climate Sciences Department Seminar

Smoke aerosol properties and ozone evolve within plumes through physical and chemical processes, impacting smoke climate and health impacts. Many of these physical and chemical processes, in theory, depend strongly on smoke concentrations. Hence, the initial concentrations and dilution rates should affect smoke aging. In general, plumes from small fires should dilute more rapidly than those from large fires, all else equal; and in recent publications, we have used theory to demonstrate the smoke properties from small fires should evolve differently than those from large fires. However, until recently, we have been unable to test these findings with measurements due to a lack of Langrangian-style smoke aging field studies of small fires (due to the challenge of following small, fast-diluting plumes with time). In this talk, I will discuss how we have used observations of concentration gradients in large plumes from the Pacific Northwest portion of BBOP campaign to test these hypotheses. Using the high time resolution BBOP measurements, we have separated the dilute edges of the large plumes from the concentrated cores. We expect that the dilute edges of large plumes have similar chemical and physical process rates as small, fast-diluting plumes. The BBOP data show that the dilute portions of plumes (1) have faster number losses and diameter growth from coagulation, (2) transition more quickly POA-like to SOA-like aerosol composition potentially through faster OA evaporation and faster photochemistry, and (3) have higher enhancements of ozone. We recommend that future smoke studies compare concentrate plume cores to dilute edges to help elucidate physical/chemical processes and understand inter-plume differences.