Fire emission heights in the climate system - Part 2: Impact on transport, black carbon concentrations and radiation

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Veira, A., Kloster, S., Schutgens, N., Kaiser, J.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2015
• Subjects: Aerosol Robotic Network
• Online Access: http://hdl.handle.net/11858/00-001M-0000-0029-28A5-B

Wildfires represent a major source for aerosols impacting atmospheric radiation, atmospheric chemistry and cloud micro-physical properties. Previous case studies indicated that the height of the aerosol-radiation interaction may crucially affect atmospheric radiation, but the sensitivity to emission heights has been examined with only a few models and is still uncertain. In this study we use the general circulation model ECHAM6 extended by the aerosol module HAM2 to investigate the impact of wildfire emission heights on atmospheric long-range transport, black carbon (BC) concentrations and atmospheric radiation. We simulate the wildfire aerosol release using either various versions of a semiempirical plume height parametrization or prescribed standard emission heights in ECHAM6-HAM2. Extreme scenarios of near-surface or free-tropospheric-only injections provide lower and upper constraints on the emission height climate impact. We find relative changes in mean global atmospheric BC burden of up to 7.9 +/- 4.4% caused by average changes in emission heights of 1.5-3.5 km. Regionally, changes in BC burden exceed 30-40% in the major biomass burning regions. The model evaluation of aerosol optical thickness (AOT) against Moderate Resolution Imaging Spectroradiometer (MODIS), AErosol RObotic NETwork (AERONET) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations indicates that the implementation of a plume height parametrization slightly reduces the ECHAM6-HAM2 biases regionally, but on the global scale these improvements in model performance are small. For prescribed emission release at the surface, wildfire emissions entail a total sky top-of-atmosphere (TOA) radiative forcing (RF) of -0.16 +/- 0.06 W m(-2). The application of a plume height parametrization which agrees reasonably well with observations introduces a slightly stronger negative TOA RF of -0.20 +/- 0.07 W m(-2). The standard ECHAM6-HAM2 model in which 25% of the wildfire emissions are injected into the free troposphere (FT) and 75% ...