Measurement and modeling of oxides of nitrogen from vehicular contributors

• Main Author: Kenty, Kerstin Lesley
• Format: Others
• Published: Scholar Commons 2006
• Subjects: NOx; CALINE4; Air pollution; DOAS; NO; American Studies; Arts and Humanities
• Online Access: http://scholarcommons.usf.edu/etd/2582; http://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=3581&context=etd

The focus of this research was the examination of the emission and transformation of nitrogen oxides emitted from vehicles. Measured data for this experiment were collected from May 1 thru May 31, 2002, and were compared to values modeled with CALINE4. CALINE4 is a photochemical and dispersive model used to predict concentrations of NOX (NO+NO2) from line sources. The measurement campaign was coincident with the Bay Regional Atmospheric Chemistry Experiment (BRACE). An ambient air quality monitoring site was constructed adjacent to Gandy Boulevard, in Tampa, FL. When comparisons of measured and modeled NO and NO2 values were made it was found that CALINE4 underpredicted NO2; i.e., underpredicted the conversion of NO, for both daytime and nighttime conditions. Possible causes of this bias were investigated and it was found that the simple kinetic mechanism present in CALINE4 was not sufficient to account for all of the reactions occurring. A simulation was run with a more comprehensive NO conversion mechanism and it was found that the reactions containing peroxy radicals affected the conversion rate but were not present in the simple CALINE4 mechanism. The simulation runs suggested that the ratio of radicals to O3 remained nearly constant during the course of the reaction. This pointed to an improved mechanism where the photolytic rate constant in CALINE4 could be replaced with a new constant, keff. This brought theday time calculations within reasonable agreement of the measured values, including an unexpected improvement in nighttime concentrations. Specifically, this modification eliminated the negative fractional bias in calculated daytime NO2 concentrations, moving it from -0.16 to 0.043. The fractional bias in nighttime calculations was improved from -0.17 to -0.036. Average hourly traffic counts were then used as inputs to the model to compare to the entire month of May 2002 data and it was found that the daytime fractional bias was improved from -0.27 to -0.06 and the nighttime from -0.35 to -0.24