AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Where’s the Mass: Why Might Field and Laboratory Studies on Aging of Biomass Burning Aerosols Disagree on Mass Enhancements?
ANNA HODSHIRE, Ali Akherati, Matthew Alvarado, Benjamin Brown-Steiner, Shantanu Jathar, Jose-Luis Jimenez, Sonia Kreidenweis, Chantelle Lonsdale, Timothy Onasch, Amber Ortega, Jeffrey R. Pierce, Colorado State University
Abstract Number: 290 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract Biomass burning is a major source of atmospheric particulate matter (PM) with implications for health, climate, and air quality. As biomass burning plumes are transported downwind, the particles and vapors undergo chemical and physical aging. These aging processes can either increase or decrease total PM mass, but aging always causes changes in the PM composition (e.g. oxygen-to-carbon ratio). Field measurements of the evolution of mass with age range from decreases to increases, with most showing little to no change. Conversely, laboratory studies tend to show significant mass increases on average. Currently, there is no consensus on why field measurements tend to show little mass change, or why field and laboratory experiments give such different results for total particle mass but show similar rates of change in composition. We summarize available observations of aging smoke mass concentrations and composition markers and discuss four broad hypotheses to explain variability within and between field and laboratory campaigns: (1) variability in emissions and chemistry, (2) differences in dilution/entrainment, (3) losses in chambers and lines, and (4) differences in conditions selected as “time zero”, the baseline from which changes are estimated. Hypothesis (1) is well known and has been the subject of intensive research. Hypothesis (2) can potentially lead to greater aerosol evaporation in the field than the laboratory. Hypothesis (3) suggests there are losses of precursor vapors potentially unaccounted for, which would lead to even greater mass enhancements for the laboratory system. Hypothesis (4) indicates that if a great deal of chemistry occurs rapidly within the plume (<10 minutes), field studies that can only measure >10 minutes after emission would miss this initial mass enhancement. We show examples of the anticipated impacts of hypotheses (2)-(4) with the aim to spur community interest and further research in these areas.