Non-parametric Nature Of Ground-level Ozone
And Its Dependence On Nitrogen Oxides (NOx):
A View Point Of Vehicular Emissions
Author(s)
S. Munir, H. Chen & K. Ropkins
Abstract
Ground-level ozone has been studied extensively using classic parametric
statistics (most commonly conventional linear regression). Very few researchers
have considered ozone distributions and even those that do tend to apply
parametric techniques. This study assesses ground-level ozone distributions at
six locations in the UK and characterises the correlation of nitrogen oxides
(NOx) and ozone at a roadside location. The 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 associated
with road traffic. There is evidence that ground level ozone is not normally
distributed (p-values < 0.05). NOx is a dominant sink for ozone at urban and
roadside sites due to its ozone scavenging effects. Consistent with literature
ozone is negatively correlated with NOx. The negative correlation is stronger at
low NOx levels (up to approximately 80 ppb 24 hour 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 approximately
200 ppb or over the correlations become positive. This study investigates how
the associations of ozone and NOx vary at different levels of their mixing ratios
and suggests that due to the non-normal distribution of ozone, nonparametric
statistics should be applied for ozone modelling.
Keywords: ground-level ozone, air pollution, nitrogen oxides, nitrogen oxides
and ozone, ozone distribution, vehicular emissions and ozone.
Keywords
ground-level ozone, air pollution, nitrogen oxides, nitrogen oxides
and ozone, ozone distribution, vehicular emissions and ozone
Related Book
Other papers in this volume
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