Researchers Put Model to the Test for Trans-Pacific Aerosols
Aerosols originating from natural (for example, dust and sea salt) and anthropogenic (for example, soot) sources in Europe, North Africa, and East Asia can be transported thousands of miles downwind across the Pacific Ocean to North America. Researchers, led by Department of Energy (DOE) scientists at Pacific Northwest National Laboratory (PNNL), used satellite- and ground-based observations to evaluate how well climate models simulate the trans-Pacific aerosol transport and its seasonal and annual variability.
Quantifying the ability of climate models to simulate trans-Pacific aerosol transport is an important step toward understanding its impacts on regional climate and air quality in western North America.
Led by researchers at DOE’s Pacific Northwest National Laboratory, the team used the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) to conduct quasi-global simulations for 2010–2014 to study trans-Pacific transport of aerosols and their impacts on clouds and precipitation in California. Their study provides a comprehensive evaluation of the simulations using multiple observation data sets to establish model skill in capturing long range transport of aerosols over the Pacific Ocean. The team found that the simulation generally captured the spatial and seasonal variability of satellite-retrieved aerosol optical depth (AOD) and absorbing AOD over the Pacific Ocean, which is determined by the outflow of pollutants and dust from Asia and Africa and the emissions of marine aerosols, like sea salt, from the ocean. The model also reproduced the variability of aerosol size distributions and the vertical profile of aerosol extinction and its seasonality over the Pacific, and simulated the observed dust, sulfate, and nitrate surface concentrations when compared with surface measurements over the western United States. However, the researchers noticed significant underestimation of the peak surface concentrations of carbonaceous aerosol, which is likely due to model biases in biomass burning emissions and secondary organic aerosol production. With a sensitivity simulation, they found that North American (not trans-Pacific) emissions dominated the peaks of carbonaceous aerosol surface concentrations. Overall, this study demonstrated that the WRF-Chem quasi-global simulation, a high-resolution nested regional model, can be used to provide inflow boundary conditions for investigating trans-Pacific transport of aerosols and their impact on the regional climate and air quality.