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Analysis of long-term ozone trend over Delhi and its meteorological adjustment
Kumari, S.; Jayaraman, G. & Ghosh, C.
Abstract
Present study deals with the statistical analysis
of long-term ground level ozone (O3) trend and the influence of meteorological variables on its variation over Delhi, India. Daily mean and maximum of O3and meteorological data, obtained from India Meteorological
Department, were arranged for the period of 9 years
(1998-2006). Based on the preliminary correlation study of
all the data with O3
, six variables viz. daily maximum
temperature, daily average relative humidity, dew point,
wind speed, visibility, and total sunshine were selected.
Classical additive time series decomposition technique was
used to obtain seasonally adjusted long-term trend. To
analyze the masking effect of meteorology, adjustment was
made using Kolmogorov-Zurbenko filters followed by
stepwise regression analysis to the smoothed series of O3
maximum and meteorological variables, which showed that
long-term trend was independent of sunshine duration.
Results indicate a significant increasing trend with annual
increase of 1.13 % for O3
mean and 3 % for O3
maximum.
Annual deseasonalized trend for seasonal cycle shows
bimodal oscillations. About 43 % of O3
variation was
explained by the selected meteorological factors and rest of
variation attributed to factors like emission of precursor
gases, pollutant transport, policy changes, etc. Among the
three tested regression models, performance of Model 2
with variable temperature, wind speed, and visibility was ound to be best that resulted in lowering of O3
trend. Large
variability (23 %) was explained by the variable visibility
depicted that the emission of primary pollutants not only
provides the precursor gases but also control the local
photochemical reactions.
Keywords
Ground level ozone; Kolmogorov-Zurbenko filters; Meteorological variables; Ozone mean; Ozone maximum; Time series decomposition
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