Capturing Biogenic Volatile Organic Compounds in a Coupled-Model System Compared to Observation
Zhao, Chun - Pacific Northwest National Laboratory
Area of research:
Journal Reference:Zhao C, M Huang, JD Fast, LK Berg, Y Qian, A Guenther, D Gu, M Shrivastava, Y Liu, S Walters, G Pfister, J Jin, JE Shilling, and C Warneke. 2016. "Sensitivity of biogenic volatile organic compounds to land surface parameterizations and vegetation distributions in California." Geoscientific Model Development, 9(5), 10.5194/gmd-9-1959-2016.
Current climate models still have large uncertainties in estimating biogenic (naturally emitted) trace gases, which can significantly affect atmospheric chemistry and secondary aerosol formation that ultimately influence the capacity of aerosol particles to affect Earth’s energy balance (aerosol radiative forcing) and air quality. These uncertainties result from many factors, including uncertainties in land-surface processes (exchanges of heat, water, CO2, and trace gases) and the vegetation types specified, both of which can affect the simulated near-surface fluxes of biogenic volatile organic compounds (BVOCs).
Researchers developed a modeling framework based on WRF-Chem, a popular regional model, to include BVOC emissions embedded in land-surface processes. This coupled modeling system reasonably simulated BVOCs compared to observations. The results quantified the impacts from land-surface processes and vegetation distributions on the estimated BVOCs in the atmosphere. To understand simulating BVOCs and consequently the formation of secondary organic aerosols, this study may indicate that appropriate land-cover data sets are needed for climate models, more than improved details on land processes.
In this study, researchers led by scientists at Pacific Northwest National Laboratory coupled the latest version of the Model of Emissions of Gases and Aerosols from Nature (MEGAN v2.1) within the land-surface model called Community Land Model version 4 (CLM4) in the Weather Research and Forecasting model with chemistry (WRF-Chem). In this implementation, MEGAN v2.1 shares a consistent vegetation map with CLM4 for estimating BVOC emissions. They used this improved modeling framework to investigate the impact of two land-surface schemes, called CLM4 and Noah, respectively, on BVOCs and examine the sensitivity of BVOCs to vegetation distributions in California. The measurements they used provide an opportunity to evaluate the simulated BVOCs and were collected during the DOE-sponsored Carbonaceous Aerosol and Radiative Effects Study (CARES) and the NOAA-sponsored California Nexus of Air Quality and Climate Experiment (CalNex) conducted in June of 2010. Their sensitivity experiments showed that land-surface schemes do influence the simulated BVOCs, but the impact is much smaller than that of vegetation distributions. This study indicates that more effort is needed to obtain the most appropriate and accurate land-cover data sets for climate and air-quality models in terms of simulating BVOCs, oxidant chemistry, and consequently secondary organic aerosol formation.