Modeling of ozone precursors and their transformation into ground-level ozone in urban environment in Malaysia
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Date
2010
Authors
Ghazali, Nurul Adyani
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Abstract
Ozone (03) is one of the major problems of air pollution around the world due to its
ability to cause adverse effect to human health and environment. Hence, it is
important to develop 0 3 prediction model to give the early warning to public. The
hourly observations of 0 3 and nitrogen oxides (N Ox) concentrations together with the
weather parameters were monitored from five study areas in Malaysia. The
observations were obtained over five year period from 2003 to 2007. Times series
plot was used to explain the transformation of nitrogen dioxide (N02) into 0 3 at
urban environment of Malaysia. The findings proved that the peak concentration of
0 3 occurs during noon when highest UVB intensity and temperature recorded. By
using multiple linear regression analysis, 0 3 prediction daytime and night time
models for each study areas were developed based on its precursors; N02
concentration, nitric oxide (NO) concentration, Non-methane Hydrocarbon (NmHC),
total hydrocarbon (THC) and also meteorological parameters such as ultraviolet
radiation (UVB), temperature, humidity, wind speed and wind direction as the
predictors. These data were analyzed using linear regression methods in order to set
up the tool for future prediction of 0 3 concentration. Coefficient of determination
(R 2
) was calculated to show the degree of linearity between 0 3 concentrations with
other prediction variables. From the regression model, the predicted values of 0 3
concentration were observed. Prediction of 0 3 concentrations was carried out and
scatter plot of observed 0 3 concentrations versus predicted 0 3 concentrations was
plotted for developed models verification. Among the meteorological parameters,
UVB and temperature tend to contribute significantly to high 0 3 concentrations.
Besides that, wind speed and wind direction also affect the accumulation of precursor
and affect the 0 3 concentrations indirectly. The influences of the different previous
hour 0 3 concentrations on the next hour concentrations was also demonstrated and
proved that previous one hour 0 3 concentrations influence the most for the next hour
concentrations. Performance indicators analysis was then carried out based on the
normalised absolute error (N AE), prediction accuracy (P A), coefficient of
determination (R2), root mean square error (RMSE) and index of agreement (IA) and
the best fit models for all the three study areas were determined. To determine the
accuracy of the values, plots of predicted 0 3 concentration against observed 03
concentration were done. The 95 %confidence interval was found. From the study,
the measured coefficients of determination for all models are above 0.8; however the
overall accuracy for predicted models is approximately 95 %.
Description
Keywords
Ozone precursors , Urban environment