Séminaire

Evaluation of WRF-Chem simulations of carbonaceous and inorganic aerosols over California using measurements from the 2010 CARES and CalNex field campaigns 

Jerome Fast, Vinoj Velu, Ying Liu, Rahul Zaveri, and Manish Shrivastava.

The WRF-Chem community model is used with a 4 km grid spacing to simulate the evolution of carbonaceous and inorganic aerosols and their impact on radiation during May and June of 2010 over California when two field campaigns took place: the California Nexus Experiment (CalNex) and Carbonaceous Aerosol and Radiative Effects Study (CARES). We merged CalNex and CARES data along with data from operational networks such as, California Air Resources Board (CARB’s) air quality monitoring network, the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, the AErosol RObotic NETwork (AERONET), and satellites into a common dataset for the Aerosol Modeling Testbed. The resulting combined dataset is used to rigorously evaluate the model simulation of aerosol mass, size distribution, composition, and optical properties needed to understand uncertainties that could affect regional variations in aerosol radiative forcing. In this study, aerosols in WRF-Chem are simulated by the MOSAIC model that uses a sectional approach to represent the aerosol size distribution and the volatility basis set approach to represent secondary organic aerosol (SOA).

The model reproduced many of the diurnal, multi-day, and spatial variations of aerosols as seen in the measurements; however, the performance varied by region and some aerosol species (sulfate and nitrate) were better represented than others (organic matter, black carbon) at many locations. The vertical distribution of aerosols was simulated reasonably as evidenced from comparison with observed profiles from the High Spectral Resolution Lidar (HSRL) on the NASA B-200 aircraft. While the simulated aerosol mass in the boundary layer was usually too low, the simulated column aerosol optical depths from the HRSL and at the AERONET and field campaign sites were often too high. A sensitivity simulation shows that this bias results from the long-range transport of aerosols in the free troposphere from Asia into North America that is likely too high. The radiative effect of simulated aerosols and its sensitivity to the uncertainties in predicted aerosol properties will also be presented.

Jerome.Fast@pnnl.gov