Dissertation/Thesis Abstract

Regional Air Quality and Climate Modeling using WRF/Chem with Improved Model Representations of Organic Aerosol Formation and Aerosol Activation
by Yahya, Khairunnisa Binte, Ph.D., North Carolina State University, 2016, 515; 10970040
Abstract (Summary)

The Weather Research and Forecasting model with Chemistry (WRF/Chem) is an online-coupled model which considers feedbacks from meteorology to chemistry, and vice versa, as well as aerosol-cloud-radiation feedbacks. The WRF/Chem model is therefore able to model both air quality and regional climate simulations. This study involves the application, evaluation, and improvement of the WRF/Chem model over the continental U.S. (CONUS). Comprehensive operational, diagnostic, and mechanistic evaluations of the WRF/Chem model are carried out for 2001, 2006, and 2010. The WRF/Chem model performs well in general for Ozone (O 3) and fine particulate matter (PM2.5), as well as for most surface meteorological variables except for precipitation. Air quality trends from 2001 to 2010 are also analyzed to quantify the impacts of the changes in emissions for this decade. The WRF/Chem model is also applied for decadal regional climate simulations. The Community Earth System Model (CESM) model is downscaled by providing meteorological and chemical inputs to the WRF/Chem model for current and future decade simulations based on the Representative Concentration Pathways (RCP) scenarios for RCP4.5 and RCP8.5. A comprehensive decadal climatological evaluation is carried out to assess the model performance for current climate simulations. The results from the WRF/Chem model are compared to the results from the WRF model to assess the impacts of feedbacks from chemistry to future climate. Both WRF/Chem and WRF model show about ~2 °C increase in 2-m temperature (T2) in the year 2050, however, the location of the maximum T2 and precipitation differs for different models and RCP scenarios, due to the influence of the magnitude and spatial variability of aerosols in WRF/Chem. The WRF/Chem simulations also show a non-linear trend for changes in O3 mixing ratios due to the changes in greenhouse gases, nitrogen oxides (NOx), volatile organic compounds (VOCs), and O3 indicator regimes in the future. The RCP4.5 scenario shows mainly a decrease in O3 mixing ratios over most parts of CONUS except for several urban areas, while the RCP8.5 scenario shows increases in O3 mixing ratios over the whole CONUS, due to increases in temperature, solar radiation, and biogenic VOCs, and methane (CH4) levels. The representation of aerosol-radiation-cloud processes in WRF/Chem are important not only for air quality, but also for climate simulations. The aerosol-cloud variables, such as the cloud droplet number concentration (CDNC) are not well-represented in the model. Large uncertainties remain in the representations of aerosols and clouds in the model, including the secondary organic aerosol (SOA) formation processes as well as the aerosol activation parameterization in the model. The organic aerosol (OA) formation process based on the Volatility Basis Set (VBS) is improved by including semi-volatile primary organic aerosol (POA) as well as fragmentation and functionalization processes. An improved aerosol activation parameterization based on Foutoukis and Nenes (2005), Barahona and Nenes (2010), and Morales Betancourt and Nenes (2014) is incorporated into the model as an alternative to the default Abdul Razzak and Ghan (2000) treatment. However, the results show that the improved parameterization reduces the bias but increases the errors for CDNC over CONUS, due to existing model weaknesses in simulating AOD and CCN, as well as possible inaccuracies in the spatial distribution and magnitudes of particulate matter emissions in the upper model layers. Future work is needed to consider improvements in the spatial variability of column PM and CCN to improve CDNC predictions in the model.

Indexing (document details)
School: North Carolina State University
Department: Marine, Earth and Atmospheric Sciences
School Location: United States -- North Carolina
Source: DAI-B 80/01(E), Dissertation Abstracts International
Subjects: Atmospheric Chemistry, Atmospheric sciences
Keywords: Aerosol activation, Air quality, Atmospheric modeling, Climate, Organic aerosol, Wrf/chem
Publication Number: 10970040
ISBN: 978-0-438-28497-5
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