10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Effects of Atmospheric Chemical Aging on Biomass Burning Aerosol Composition and Ice Nucleating Properties
LYDIA JAHL, Michael Polen, Leif Jahn, Thomas Brubaker, Ryan Sullivan, Carnegie Mellon University
Abstract Number: 973 Working Group: Unraveling the Many Facets of Ice Nucleating Particles and Their Interactions with Clouds
Abstract Biomass burning is a major global source of aerosol pollution that comprises nearly 80% of the total carbonaceous aerosol burden and 2700 Gg of black carbon emissions per year. The ability of some aerosol particles to nucleate ice was once thought to only occur in mineral dust and biological particles, but recent studies found that some types of biomass burning aerosol (BBA) can also nucleate ice and cause the glaciation of clouds. Cloud glaciation causes changes in the evolution of a cloud’s properties and structure by initiating precipitation, influencing atmospheric chemical reactions, changing cloud lifetime and size, and altering the cloud’s radiative forcing. We seek to understand what chemical properties of the aerosol particles might explain the nucleation of ice at mixed-phase cloud temperatures. Furthermore, many studies focus on the ice nucleating abilities of fresh, unaged aerosol that may not represent realistic BBA, which experiences significant chemical processing and aging. Therefore, we explored the relationships between the ice nucleating abilities and chemical properties of authentic biomass burning aerosol that we chemically aged in an environmental chamber.
We burned biomass fuels that are commonly consumed in wildfires and prescribed burns such as sawgrass, birch, and black needlerush to fill an environmental smog chamber with biomass burning aerosol smoke. The aerosol was aged using three different chemistries: hydroxyl radical aging by injection of nitrous acid with UV lights, dark ozonolysis, and by hydroxyl radical aging of aerosol particle surfaces only by first passing the aerosol through a thermal denuder to remove organic components. In several systems, hydroxyl radical aging was found to enhance the aerosol’s ice nucleation properties. For example, the ice active site density of cutgrass BBA increased by half an order of magnitude following oxidation corresponding to a 10% increase in the O:C ratio of the aerosol. However, this was not an effect consistently observed for all biomass fuels tested. The chemical composition of the aerosol was analyzed using two single-particle mass spectrometers (SP-AMS and LAAPTOF), and the particles were collected on filters for SEM/EDX analysis and to determine their ice nucleating abilities. We analyzed the ice nucleating properties of the biomass burning aerosol on a cold plate using two different droplet generation techniques: droplets directly pipetted into an oil bath and droplets stored and created on a custom microfluidic chip. We will present our findings on the changes in the aerosol’s composition following chemical aging, and will correlate the ice nucleating abilities of different plant species’ fresh and aged emissions to their aerosol chemical composition.