2016 Progress Report: Interplay Between Black and Brown Carbon from Biomass Burning and ClimateEPA Grant Number: R835883
Title: Interplay Between Black and Brown Carbon from Biomass Burning and Climate
Investigators: Murphy, Shane Michael
Institution: University of Wyoming
EPA Project Officer: Chung, Serena
Project Period: January 1, 2016 through December 31, 2018
Project Period Covered by this Report: January 1, 2016 through December 31,2016
Project Amount: $349,847
RFA: Particulate Matter and Related Pollutants in a Changing World (2014) RFA Text | Recipients Lists
Research Category: Air , Climate Change
The objectives of this project are to determine the wavelength-resolved single scattering albedo (SSA), absorption, and extinction along with the chemical and physical properties of aerosol emissions from biomass burning (wildfires) in the Western United States. These data enable us to determine the contribution of black versus brown carbon to observed aerosol absorption and quantify the enhancement of black carbon absorption caused by organic coatings. We utilize these new in-situ observations to update the refractive indices of organic and black carbon aerosol from biomass burning in the NCAR Community Atmosphere Model (CAM5) and assess the regional and global climate impacts of improved optical properties under a range of future biomass burning scenarios. In particular, we investigate the current and future radiative forcing and climatic effect from brown carbon absorption utilizing CAM5.
The major accomplishments during this reporting period are:
1. A novel, particle-based, calibration method for multi-pass photoacoustic absorption spectrometer (PAS) instruments.
2. Modification of the Community Atmosphere Model (CAM 5.4) to enable determination of brown carbon refractive index from the black carbon to organic aerosol (BC/OA) ratio.
3. Isolation of optical properties for biomass burning emissions in the Community Earth Systems Model Version 1 (CESM1) equipped with CAM 5.4 and discovery that the relationship of SSA to the black carbon to total carbon ratio (BC/(OC+BC)) in the model are significantly different than laboratory results at longer wavelengths, but similar at 400 nm.
The first of these results will impact the broader atmospheric science and air quality community by providing a particle-based calibration technique for all multi-pass PAS instruments. The second is the first attempt, that we are aware of, to implement brown carbon optical properties into a global climate model utilizing published relationships between brown carbon and BC/OA. The third result was a surprise and motivates the field studies to be conducted in summer 2017 and 2018, which will clarify why model results are significantly different than laboratory measurements. It is critical to understand and improve the optical properties of biomass burning emissions in global models to have confidence in this forcing in future climates where biomass burning emissions will be a significant forcing agent.
During the next reporting period our major activity will be to deploy the University of Wyoming mobile lab equipped with the 4-wavelength photoacoustic absorption spectrometer (PAS), 2-wavelength cavity attenuated phase shift – single scattering albedo (CAPS-SSA), scanning mobility particle sizers (SMPS), and aerosol mass spectrometer (AMS) instruments to multiple wildfires in the Western United States. These data will be analyzed and the resulting analysis will give insight into the existing discrepancies between CAM 5.4 and laboratory generated optical properties. We will use these insights to modify the CAM 5.4 model and assess the impact of these modifications on direct radiative forcing. It is anticipated that these activities will result in an additional two publications, one focused on the field data and analysis and one focused on the modeling activity.