Issue 3

It is well known that the studies that associate the climatic changes with the greenhouse
effect, as a sequence of uninterruptedly ongoing figures in the concentration mainly of carbon
dioxide, have been focused on the trends of the mean temperature. On the other hand the
variability and the trends of the extreme temperature values have not been considered
sufficiently. We notice that the variability of the maximum and minimum temperature values
and generally of the extreme weather has direct economic and societal implications.
The interest in this paper is focused on the study of the trends of the daily and the monthly
maximum temperature during the warm months July and August for the time period from 1955
to 2000 in the wide Athens area and specifically measurements of the Nea Philadelphia and
Helliniko meteorological stations. Nea Philadelphia represents an immiscibly urban area
station, while Helliniko a coastal suburban area one. The specific sites were selected for the
comparative study of the temperature maximum trends in a time period which covers the
population growth in the area of Athens.
For the whole time period, the differences of the daily maximum temperature from the
corresponding 10-days period mean maximum temperatures per month were calculated for
each site. Then, the days with positive difference per month and per year as well as the
trends of the time-series for each station were recorded along with the statistical significance
of the regression slope’s value using the Student t-test distribution.
Furthermore, in order to identify the “warmest decade” in the time-series, a study of the daily
maximum temperature trend for the months July and August was performed for each decade
followed by a test for the statistical significance of the slope coefficient.
It is known that the presumable differences of the temperature time-series depend on the
influence of the urbanization, the modification of the natural suburban environment and / or on
the stations’ displacement. Based on these facts, we present more in this paper the
conclusions of a comparative study of the results regarding each station analytically as well
as the interpretation of the results concerning all the stations as an ensemble.

Results of the total column ozone and ultraviolet (UV-B) erythemally weighted irradiance
measurements at the ground-based solar monitoring station at the Kishinev (Moldova) are
presented. Diffuse and global components of solar UV-B erythemal irradiance on horizontal
plane were continuously measured with sensors UV-S-B-C (of broadband 280-315 nm),
Kipp&Zonen. Monthly totals of global and diffuse components of solar UV-B erythemal
radiation reveal distinct seasonal variation with respective minimum in winter and maximum in
summer. Typical values for these components in limiting cases are presented. A simple
polynomial relationship between the global and diffuse components of solar UV-B erythemal
radiation measured for cloudless days was derived. It was shown that coefficients of the
polynomial depend on daily mean value of aerosol optical thickness (AOT). Collocated
measurements of AOT have been carried out with the sunphotometer Cimel CE-318 within
the framework of the Aerosol Robotic Network (AERONET) program, managed by
NASA/GSFC.
Total column ozone content was retrieved from direct solar ultraviolet radiation measurements
at 3 discrete wavelengths centered at 305.5, 312.5, and 320 nm within the UV-B range.
Ozone measurements were regularly carried out with the hand-held MICROTOPS II
Ozonemeter, Solar Light Co. Monthly average values of total column ozone content
measured with the MICROTOPS II at the Kishinev are in close agreement with those ones
retrieved from the multiyear (1978-2004) database statistics acquired from satellite platforms
measurements with the Total Ozone Mapping Spectrometer (TOMS). It was shown the
existence of seasonal variability of the total column ozone content with respective minimum
values observed at the end of autumn and winter, and maximum values observed at the end
of winter and in spring. The maximum and minimum of daily mean values of total column
ozone ever measured with TOMS at the satellite platforms overpassed Kishinev site,
amounted of ~540 DU (on February 19, 1985) and ~204 DU (on December 1, 1999). Yearly
mean value of total column ozone measured at the Kishinev was ~ 338 DU. Total column
ozone measurements carried out with MICROTOPS at the Kishinev site from September
2003 to August 2004, gave maximum and minimum values of ozone daily means at ~ 489 DU
(on February 12, 2004) and ~259 DU (on December 3, 2003). The estimation of total column
ozone trend derived from the TOMS multi-year statistics was ~ -10 DU/decade.

Records of precipitation in Macau are collected from three local monitoring stations from 1993
to 2003. Chemical compositions of precipitation are analyzed to reveal the causes of wet
deposition in Macau. The review of annual rainfall volumes and the volume weighted annual
pH values over this period show that there is a slight spatial variation in the rainfall volume
and the entire area of Macau is subjected to acidic precipitation. The monthly rainfall volumes
and the monthly concentrations of five ionic species including H+, nssSO4
2-, NO3
-, nssCa2+,
and NH4
+ are analyzed statistically and their distributions are found to have positive skewness
and kurtosis. The monthly rainfall volume is found to follow the Gamma distribution which is
consistent with the findings in other regions of Asia. In addition, the monthly concentration of
each ionic species is found to follow the lognormal distribution. Nonetheless, the distribution
of each ionic species exhibits spatial variability across the stations. Therefore, it is suspected
that the sources of wet acid deposition in different parts of Macau are different and further
correlation analysis on the values of [H+], nss[Ca2+], [NH4
+], nss[SO4
2-], and [NO3
-] of the
precipitation is carried out.
Correlation analysis on the monthly concentrations of the ionic species shows that the linear
correlation between [H+] and nss[SO4
2-] is higher than the linear correlation between [H+] and
[NO3
-] at two of the monitoring stations. The result indicates that sulfur dioxide could be a
relatively important contributor of acid wet deposition with respect to nitrogen dioxide in
Macau as suggested by previous preliminary studies. In addition, the eleven-year averaged
ratio of [SO4
2-]/[NO3
-] at Ka-Ho being 5.06 reinforces this conclusion. However, the dominant
sources contributing to the acidity in two regions of Macau, namely Fortaleza and Taipa
Grande respectively are still unknown since the anions do not show any significant positive
correlation to the hydrogen ion at these two stations. It is only ascertained that the dominant
source of acidity in Ka Ho can be originated from the emission of SO2 as the relatively strong
linear correlation of [H+] and nss[SO4
2-] indicates that the free acidity is mainly contributed
from the sulfuric acid. For the other stations, the wet acid deposition is then believed to be
controlled by local sources of sulfuric acid, nitric acid and some other acids that are not
accounted for in the present study. Finally, the monthly concentrations of the ionic species are
found to be negatively correlated with the monthly rainfall volume at three monitoring stations.
Hence, it is concluded that longer rainfall duration would reduce the acidity in rainwater.

Probability density functions (pdf) have been used in the analysis of the distribution of
pollutant data, for examining the frequency of high concentration events. There have been
very few studies on the concentration distribution of PM in urban areas. The distribution of PM
concentrations has an impact on human health effects and the setting of PM regulations.
Eight probability distribution functions were fitted to measured concentrations of PM10 and
PM2.5 in order to determine the shape of the concentration distribution. The “goodness-of-fit”
of the probability density functions, to the data, was evaluated, using various statistical indices
(including Chi-square and Kolmogorov-Smirnov tests). The evaluation was conducted for two
separate years and the results indicated that the Pearson type VI pdf provided a better fit to
the measured data. Other functions exhibiting high accuracy of fit were the inverse Gaussian,
the lognormal and Pearson type V.
The possibility to use probability density functions for predicting the daily high concentration
percentiles to less than everyday sampling scenarios is also shown. The differences in the
distribution of concentrations under these scenarios are important for regulatory compliance.
When trying to detect the high concentrations there is significant possibility of missing the
events and thus, underestimating the number of exceedances occurred. Significant deviations
from actual daily measurements of PM10 and PM2.5 concentration percentiles were observed,
when infrequent sampling scenarios were examined. The differences were higher for the 1-in-
6 sampling schedules and reached 2.8% for mean PM10 and 8% for PM2.5 while for the
maximum concentrations the respective differences were 21.3% and 31.9%. Differences
between the frequency distributions of everyday and non-everyday sampled concentrations
were observed, while lognormal and inverse Gaussian functions provided a better
approximation of the upper percentiles.
Fitting infrequent data on continuous probability functions for the improvement of the
approximation to the real statistical values provided good results regarding the 90th percentile,
which corresponds to the E.U. provision of 35 annual exceedances of 24-h limit PM10 values.
In the case of the extreme 98th and 99th percentiles, the method provided satisfactory results
for both the PM10 infrequent sampling scenarios.