Abstract
A one-year series of hourly average PM10 observations, which was obtained from the urban and national park air monitoring station at Taipei (Taiwan), was analyzed by descriptive statistics and fractal methods to examine the temporal structures of PM10 concentrations. It was found that all PM10 measurements exhibited the characteristic right-skewed unimodal frequency distribution and long-term memory. A monodimensional fractal analysis was performed by transferring the PM10 concentration time series into a useful compact form: the box-dimension (D(subscript B))-threshold (T(subscript h)) and critical scale (C(subscript S))-threshold (T(subscript h)) plots. Scale invariance was found in these time series and the box dimension was shown to be a decreasing function of the threshold PM10 level, implying multifractal characteristics, (i.e., the weak and intense regions scale differently). To test this hypothesis, the PM10 concentration time series were transferred into multifractal spectra, i.e, the π(q)-q polts. The analysis confirmed the existence of multifractal characteristics. A simple two-scale Cantor set with unequal scales and weights was then used to fit the calculated π(q)-q plots. This model fits well with the entire spectrum of scaling exponents for the examined PM10 time series. The relationship between the fractal parameters and classical statistical characteristics, as well as some problems concerning the applicability of fractal methods on air pollution, are discussed.
Highlights
PM10 is defined as particles with an aerodynamic diameter of approximately 10 μm or less, which means they can be inhaled
The coefficient of variation indicates the variability of PM10 concentration air quality mean/ coeff. of coeff. of p1 monitoring station μg/m3 variation (%) skewness l1 Range of α
The coefficient of skewness measures the relative skewness of PM10 concentration frequency distribution; a positive value means that the distribution has a long tail extending to the right
Summary
PM10 is defined as particles with an aerodynamic diameter of approximately 10 μm or less, which means they can be inhaled. The persistence of PM10 pollution is a result of industrial and societal developments, but is influenced by meteorological factors (van der Wal and Janssen, 2000). In Taiwan, the levels of PM10 and other air pollutants are measured by the Taiwan Air Quality Monitoring Network (TAQMN). The Pollutant Standards Index (PSI) is used to inform the public about the current air quality and its health effects. It is found that in Taipei, two major contributors to high PSI values (poor air quality) are ozone (O3) and PM10. Because recent epidemiological studies have shown that suspended particulate matter influences respiratory health considerably (Dockery et al, 1993), it is important to examine how to effectively reduce atmospheric PM10 concentrations in order to decrease its adverse health effects
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