Investigating ozone episodes in Portugal: a wavelet-based approach

Revista Brasileira de Meteorologia, 2012

Ozone plays a very important role in the nature due its characteristics as a natural filter of ultraviolet solar radiation. Thus, it is pertinent for the scientific community to understand all natural influence factors involving ozone along with a large time series. In this work, a reconstruction of ozone time series obtained by Brewer spectrophotometer from 1994 to 2008 at the Southern Space Observatory (SSO) -29ºS, 53ºW -Southern Brazil is presented. TOMS-OMI data were used to follow the days without data, where a coefficient of correlation between TOMS-OMI and Brewer is acceptable around r = 0.89. Besides, wavelet analysis to determine the temporal evolution of the frequencies and the amplitudes was applied. Moreover, wavelet analysis aiming to determine the temporal evolution of the frequencies and the amplitudes was performed. The results pointed a period of 365 days (1 yr) for the seasonal variation of ozone, of 600 days attributed for a possible QBO influence and two periods of 2000 and other 4000 days regarding possibly to the second harmonic of the 11-year solar cycle.

Atmospheric Environment, 2015

Environmental Pollution, 2012

A very high ozone episode with observed hourly values above 350 mg m À3 occurred in July 2005 at the Lamas d'Olo air quality monitoring station, located in a mountainous area in the north of Portugal. Aiming to identify the origin and formation of this ozone-rich episode, a statistical analysis and a modelling approach were applied. A cross-spectrum analysis in the frequency domain and a synoptic analysis of the meteorological and air quality time series were performed. In order to go further in this analysis, a numerical modelling approach was applied. The results indicate that the transport of ozone and its precursors is the main responsible for the high ozone concentrations. Together with the local mountain breeze and subsidence conditions, the sea-breeze circulation transporting pollutants from the coastal urban and industrialized areas that reach the site during late afternoon turn out to be the driving forces for the ozone peaks.

Ozone plays a very important role in the nature due its characteristics as a natural filter of ultraviolet solar radiation. Thus, it is pertinent for the scientific community to understand all natural influence factors involving ozone along with a large time series. In this work, a reconstruction of ozone time series obtained by Brewer spectrophotometer from 1994 to 2008 at the Southern Space Observatory (SSO)-29ºS, 53ºW-Southern Brazil is presented. TOMS-OMI data were used to follow the days without data, where a coefficient of correlation between TOMS-OMI and Brewer is acceptable around r = 0.89. Besides, wavelet analysis to determine the temporal evolution of the frequencies and the amplitudes was applied. Moreover, wavelet analysis aiming to determine the temporal evolution of the frequencies and the amplitudes was performed. The results pointed a period of 365 days (1 yr) for the seasonal variation of ozone, of 600 days attributed for a possible QBO influence and two periods of 2000 and other 4000 days regarding possibly to the second harmonic of the 11-year solar cycle.

Atmospheric Environment, 2000

Spectral analysis is used to investigate the troposheric ozone formation and decomposition processes. Although ozone is a reactive, secondary air pollutant, a similar method of examination is used for elemental carbon which can be applied to ozone time series. To detect the reason for extreme high ozone concentrations in summer, the data was divided into low-frequency seasonal component and high-frequency component. The latter has been evaluated by using the corresponding power density spectrum. It is shown that meteorological large-and synoptic-scale #uctuations a!ect the ozone concentrations at all monitoring locations. In the data set of 1993}1995 this in#uence contributed peaks at cycle durations of 16}35 day peaks in the power density spectrum estimated from the ozone data. The level of the seasonal component at a particular site depends on the level of local in#uence by tra$c and industry emissions. The power density spectrum of the mean early morning ozone concentration (2}4 a.m.) at a measurement site situated 324 m elevation is very similar to the power spectra of the ozone data at all other monitoring locations in 1995. This a$rms the dominance of spatial homogenous #uctuations and indicates a relative uniform residual layer over a large region.

Neural Computing and Applications

In recent years, air pollution has been a major concern for its implications on human health. Specifically, ozone (O 3) pollution is causing common respiratory diseases. In this paper, we illustrate the process of modeling and prediction hourly O 3 pollution measurements using wavelet transforms. We split the time series of O 3 in daily intervals and estimate scale and wavelet coefficients for each interval by the discrete wavelet transform (DWT) with Haar filter. Subsequently we apply cumulated autoregressive integrated moving average (ARIMA) to estimate the coefficients and forecast their evolution in future intervals. Then the inverse discrete wavelet transform is implemented for the reconstruction of the time series and the forecast in the near future. In order to assess the performance of the proposed methodology, we compare the predictions obtained by the DWT-ARIMA with those obtained by the ARIMA model. Several theoretical results are shown through a simulation study. Keywords Ozone (O 3) Á Discrete wavelet transform (DWT) Á Haar wavelet Á Autoregressive integrated moving average (ARIMA) Mathematics Subject Classification 62M10 Á 42C40 Á 91B76

Arabian Journal of Geosciences, 2019

The stratospheric ozone behavior is of great importance for the shelter of life on the earth's biosphere from harmful UV radiation. A wavelet technique and explorative analysis are applied on ozone monthly time series data set from 1970 to 2013 for the stratospheric region of Pakistan. Such analysis was performed in order to fully characterize the distinct time-frequency ozone variability. Moreover, in the analysis of ozone irregularity, the main frequency constituents in the data set are estimated by the global wavelet scale. The results obtained in this investigation confirmed particular patterns that could be used to describe the regional condition of ozone. The wavelet approach illustrates a strong power spectrum along with the 2-16-month cycle, indicating an annual oscillation of 12 months for whole data set, which is investigated by the peak of the integration of time average of power over time that also reveals powerful annual pulses. The low variance period results in a band emphasized the presence of variation for seasonal interval of stratospheric ozone for each month starting from January to December. The main objective of this paper is to study the dynamics of ozone concentration at the atmospheric region of Pakistan. It also aims to examine the role of the particular ozone concentration patterns indicating inter-annual irregularity of Ozone status.

Remote Sensing of Environment, 2011

This paper focuses on the spatial-temporal structure of total ozone column (TOC) over Portugal. This relevant region of southwestern Europe has not been evaluated yet in detail due to the lack of continuous and wellcovered ground-based TOC measurements. The data used in this study are derived from the NASA's Total Ozone Mapping Spectrometer (TOMS) for the period 1978-2005. The TOC spatial behavior shows no significant longitudinal variability (smaller than 3%). In contrast, the variation in latitude changes between 3.5% and 6% depending on the calendar month. The TOC in the northern Portugal is, on average, higher than that recorded in the South. The temporal variability was analyzed for three scales: long-term, seasonal and short-term. The long-term TOC changes are analyzed between 1978 and 1999 by means of linear least squares fits. The results show an annual TOC trend of (−2.65 ± 0.70)%/decade which is statistically significant at the 95% confidence level. This TOC decrease is smaller than the trends obtained in other midlatitudes regions which could be partially explained by the compensation due to the observed increase in the tropospheric ozone over the Iberian Peninsula. A trend analysis performed for each individual month shows a statistically significant TOC decline between March and October, with a maximum linear trend value of (−7.30 ± 1.45)%/ decade in May. The amplitude of the seasonal TOC cycle over Portugal shows a slight dependence in latitude, varying from 28.6 DU (37.5°N) to 33.6 DU (41.5°N). Finally, the short-term variability showed a notable seasonal behavior, with maximum day-to-day TOC changes in winter (~6%) and minimum in summer (~3%). In addition, the persistence (characterized by the autocorrelation coefficients) strongly decreases after a few days (except in summer months).

Tropospheric ozone is a secondary pollutant having a negative impact in health and environment. To control and minimize ozone concentrations, European Community established regulations, defining in the Directive 2008/50/CE, of May 2008, in order to promote a clear air all over Europe. The aim of this work is to identify the origin of ozone episodes in Portugal, in particular, the ozone episodes associated to stratospheric intrusions. This paper will present the analysis of ozone data series between 1988 and 2010 by statistical methods and specific criteria. This work allows the identification of 303 ozone episodes with an eventual stratospheric or transboundary advection signature. The majority of these episodes occurred in

Air Pollution XXII, 2014

Ozone (O 3) is a secondary pollutant mainly produced in the troposphere by photochemical reactions with high impact on human health. In this work hourly average O 3 concentrations from the Portuguese air quality network collected during 24 years (1988-2011) were analysed. The background time series were assessed by environment type (urban, suburban and rural) and considering several criteria: the annual mean O 3 concentration, the Directive 2008/50/EC O 3 long-term objective and the 2005 WHO Guideline for protection of human health and, finally, the hourly information threshold exceedances. The trend of annual mean O 3 concentration data and the maximum daily eight-hour mean ozone concentration data were both annually compared using an one-way ANOVA followed by a Tamhane post-hoc comparison test. In both series, although of an instable trend, a tendency for an increase of the mean O 3 concentrations was found. On the other hand, after 2006, for all stations types, the normalized number of exceedances for public O 3 information are significantly decreasing (p<0.05). In this paper, the O 3 trend will be analyzed and discussed, contributing to improve knowledge of long time series of O 3 concentrations in Portugal.