Portland State University
Modeling of Ultrafine Particle Emissions and Ambient Levels for the Near Roadside Environment.
Degree: MS(M.S.) in Environmental Science and Management, Environmental Science and Management, 2017, Portland State University
Various epidemiological studies have linked exposure to Ultrafine Particles (UFP; diameter< 100 nm) to adverse health impacts. Roadway traffic is one of the major sources of UFPs and heavily influences UFP concentrations in the nearby vicinity of major roadways. Modeling efforts to predict UFPs have been limited due to the scarcity of reliable information on emissions, lack of monitoring data and limited understanding of complex processes affecting UFP concentrations near sources.
In this study continuous measurement of ultrafine particle number concentrations (PNC) and mass concentrations of nitric oxide (NO), nitrogen dioxide (NO2) and PM2.5
was conducted near an arterial road and freeway at different seasons and meteorological conditions and integrated with traffic count data. PNC showed high correlation with NO (r=0.64 for arterial; 0.61 for freeway), NO2 (r=0.57 for arterial; 0.53 for freeway) and NOx (NOx=NO+NO2; r=0.63 for arterial; 0.59 for freeway) and moderate to low correlation with traffic volume (r=0.33 for arterial; 0.32 for freeway) and PM2.5
(r=0.28 for arterial; 0.23 for freeway); respectively; for both sites at 15 minute averages. The PNC-NOx relationship prevailed on a shorter term (15 min), hourly, and throughout the day basis. Both PNC and NOx showed comparatively higher correlation with traffic during the morning period but became lower during evening which can be attributed to the higher boundary layer and wind speeds. The variable meteorology in the evening affects both PNC and NOx concentrations in the same way and the correlation between NOx and PNC is maintained high both during morning (r=0.74 for arterial; 0.69 for freeway), and evening (r=0.62 for arterial; 0.59 for freeway) periods. Thus nitrogen oxides can be used as a proxy for traffic-related UFP number concentration reflecting the effect of both traffic intensity and meteorological dilution.
The PNC-NOx relation was explored for various meteorological parameters i.e. wind speed and temperature. It is found that NOx emission is temperature independent and can be used to reflect the effect of traffic intensity and meteorological dilution. Once the effect of traffic intensity and dilution is removed, the effect of temperature on PNC-NOx ratio becomes important which can be attributed to the variation in PNC emission factors with temperature.
The high morning PNC-NOx ratio found at the arterial road is a result of new particle formation due to lower temperature and low concentration of exhaust gases in the morning air favoring nucleation over condensation. This finding has important implication when calculating emission factors for UFP number concentrations. Thus it can be concluded that roadside concentration of ultrafine particles not only depends on traffic intensity but also on meteorological parameters affecting dilution or new particle formation. High concentrations of ultrafine particle number concentration close to a roadway is expected due to higher traffic intensity , as well as…
Advisors/Committee Members: Linda A. George.
Subjects/Keywords: Environmental Sciences
to Zotero / EndNote / Reference
APA (6th Edition):
Ahmed, S. (2017). Modeling of Ultrafine Particle Emissions and Ambient Levels for the Near Roadside Environment. (Masters Thesis). Portland State University. Retrieved from http://pdxscholar.library.pdx.edu/open_access_etds/3506
Chicago Manual of Style (16th Edition):
Ahmed, Sauda. “Modeling of Ultrafine Particle Emissions and Ambient Levels for the Near Roadside Environment.” 2017. Masters Thesis, Portland State University. Accessed January 18, 2018.
MLA Handbook (7th Edition):
Ahmed, Sauda. “Modeling of Ultrafine Particle Emissions and Ambient Levels for the Near Roadside Environment.” 2017. Web. 18 Jan 2018.
Ahmed S. Modeling of Ultrafine Particle Emissions and Ambient Levels for the Near Roadside Environment. [Internet] [Masters thesis]. Portland State University; 2017. [cited 2018 Jan 18].
Available from: http://pdxscholar.library.pdx.edu/open_access_etds/3506.
Council of Science Editors:
Ahmed S. Modeling of Ultrafine Particle Emissions and Ambient Levels for the Near Roadside Environment. [Masters Thesis]. Portland State University; 2017. Available from: http://pdxscholar.library.pdx.edu/open_access_etds/3506