APPLICATION OF THE AIRPACT-5 AIR QUALITY MODELING SYSTEM TO OZONE AND PM2.5 REGIONAL AIR QUALITY ISSUES

Mahshid Etesamifard

doi:10.7273/000004368

This dissertation presents two case studies that leverage a photochemical air quality forecasting system, AIRPACT-5, to assess the model response to changes in emissions. The overall objective of these two studies is to provide helpful information for policy-makers and control-planners in developing the best strategies for decreasing PM2.5 and O3 levels. In the first study, the Community Multiscale Air Quality (CMAQ) version 5.2 was used to calculate the PM2.5 concentration contribution corresponding to major port-related sources including Ocean-Going Vessels (OGV), Cargo-Handling Equipment (CHE), trucks, and locomotives, over the Puget Sound airshed. A brute-force method was used to calculate the port-related contributions, simulating a base case representing all emissions and ‘knock-out’ cases where each port-related emissions category was zeroed out. The differences between the PM2.5 levels of the base and the knock-out cases were attributed to the port-related PM2.5 source contributions for the region. These simulations were performed for four months (January, April, July, and October) over 2018, each representing one season of the year. The annual average concentration contribution results were then used to calculate population exposure over the airshed. The results indicate that controlling emissions from ocean-going vessels would have the highest impact on population exposure to PM2.5, followed by trucks, and cargo-handling equipment sources. Locomotives were shown to be the least important relatively, in terms of population exposure to PM2.5. In the second study, an ozone sensitivity analysis was performed to investigate the predominant ozone precursor emissions and chemical regime in the Tri-Cities urban area. The Decoupled Direct Method in Three Dimensions (DDM-3D) incorporated in the CMAQv5.2 air quality model was used to calculate the first- and second-order ozone sensitivity to NOx and VOC emissions, over the Tri-Cities, WA region, during 27-29 July 2016. These simulations were performed for different perturbation cases including perturbing the total emission sources over the Tri-Cities area, and perturbing mobile, area, biogenic, and point sources emissions over separate runs. Each source contribution to ozone formation was estimated by incorporating the sensitivity coefficients from the model output using a Taylor Expansion equation and zeroing out the emissions from each source. The results from perturbing the total NOx and VOC emissions over the Tri-Cities were used to generate ozone isopleths. Mobile sources exhibited the highest contributions to ozone formation of the region. The impact of mobile sources on ozone formation in the region is mostly due to O3 sensitivity to mobile sources NOx emissions. The second important source in the region, in terms of contribution to ozone formation, is the biogenic source that drive the ozone concentrations due to both NOx and VOC sensitivity. Area and point source contributions were found to have relatively smaller impacts on the ozone levels of the region. Tri-Cities ozone isopleths were generated using the sensitivity coefficients corresponding to the total NOx and VOC emissions for the region. The results show that the region is mostly NOx-sensitive. Therefore, to decrease ozone for the region, controlling the emission of NOx, especially from mobile sources, should be beneficial.

APPLICATION OF THE AIRPACT-5 AIR QUALITY MODELING SYSTEM TO OZONE AND PM2.5 REGIONAL AIR QUALITY ISSUES

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