Conference Interactive Program
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TRB 90th Annual Meeting (January 23-27, 2011)
Current Environmental Issues in Transportation
Jan 25 2011 9:30AM- 12:00PM
Hilton, International Center
Nonparametric Nature of Tropospheric Ozone and Its Dependence on Nitrogen Oxides (NOx): Viewpoint of Vehicular Emissions (11-3182)
This study assesses tropospheric ozone distribution at six locations in the UK and characterizes the correlation of NOx and ozone at a roadside location. Distribution of ozone is investigated, applying Shapiro-Wilk test and graphical presentations. The histograms are right skewed and show maximum frequency at ozone mixing ratios from 0 to 5 ppb (particularly at urban centers and roadsides locations), which is probably caused by high levels of freshly produced NOx by road traffic. NOx is a dominant sinks for ozone at urban and roadside sites due to its ozone scavenging effects. The study concludes that there is evidence that tropospheric ozone is not normally distributed (p-values < 0.05) and therefore non-parametric statistics should be used for ozone data analysis or prediction; and consistent with literature ozone is negatively correlated with NOx. The negative correlation between ozone and NOx is stronger in winter months and night time hours when the interference from meteorological variables (particularly solar radiation) is minimum; the correlation is weaker in summer months and day time hours. Moreover the negative correlation is stronger at low NOx levels (up to 80 ppb hourly mean, Spearman correlation coefficient R is ‘-0.72’) and becomes weaker as NOx levels increase (over 80 ppb R value is ‘-0.53’). When NOx mixing ratios reach as high as 200 ppb or over the correlations become positive.
Munir, Said , University of Leeds, United Kingdom
Chen, Haibo , University of Leeds, United Kingdom
Ropkins, Karl , University of Leeds, United Kingdom
Transportation Research Board. 500 Fifth St. NW, Washington, D.C. 20001
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