Elsevier

Atmospheric Environment

Volume 90, June 2014, Pages 59-70
Atmospheric Environment

Proposal for estimating ground-level ozone concentrations at urban areas based on multivariate statistical methods

https://doi.org/10.1016/j.atmosenv.2014.03.032Get rights and content

Highlights

  • •

    A methodology for accurately estimating tropospheric ozone in urban areas is proposed.

  • •

    Urban areas have not been considered homogeneous for estimation purposes.

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    Previous ozone concentration and solar radiation appear in all proposed models.

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    Chemical variables are far more relevant in the city than in the outskirts.

Abstract

This study focuses on describing ozone patterns and estimating ozone concentrations in urban settings through the classification of an urban area into homogeneous typologies, according to hourly ozone concentrations, and the development of accurate estimation models for each typology. For these proposals, a hierarchical cluster analysis was conducted in order to define homogeneous subareas, and multiple linear regressions were subsequently applied with the aim of obtaining ozone predictions, employing chemical and meteorological variables as predictors. Seville metropolitan area (Spain) is a densely populated area of the Mediterranean Basin that exhibits environmental problems related to ozone pollution episodes. Ozone exceedances are a consequence of the combination of road traffic and industry emissions with hot temperatures and high solar radiation, mainly during anticyclonic events. Cluster analysis evince that this area can be divided into 3 categories according to hourly ozone concentration in summer. Cluster 1 is comprised of monitoring stations located in the outskirts of the city of Seville; Cluster 2 corresponds to monitoring stations located within the city of Seville; and Cluster 3 is comprised of a monitoring station specialized in traffic emissions. Multiple linear regression shows that the relative weight of meteorological variables decreases when moving from the urban periphery towards the urban center, whereas the weight of chemical variables increases. Coefficients of determination (R2) values were 0.885, 0.890 and 0.830 and root mean squared error (RMSE) were 11.226, 11.874 and 11.260 μg m−3 for Cluster 1, 2 and 3, respectively.

Section snippets

Introduction and objectives

Nowadays ozone is considered as one of the most significant air pollutants owing to the fact that it severely affects plant tissues and human health. Ozone is formed as a result of photochemical reactions in presence of sunlight involving anthropogenic emissions, such as nitrogen oxides and volatile organic compounds (Crutzen, 1979, Derwent et al., 2003, Sillman, 1999). Ozone formation is favored by certain atmospheric conditions, such as atmospheric stability, high solar radiation and

Site description and data collection

Seville is located at 37°23′N; 5°58′W and 20 masl, and its metropolitan area has a population of nearly 1 500 000 inhabitants, it being the largest in the southern region of Spain (see Fig. 1a and b). This area exhibits the typical Mediterranean climate with continental features, which combines cold temperatures in winter and rather hot temperatures in summer. Minimum and maximum average temperatures range from 6.3 °C in winter to 33.8 °C in summer, respectively. Annual rainfall is very

Hierarchical cluster analysis

As can be seen in Fig. 2, two annual ozone patterns in the Seville metropolitan area are confirmed, one of which is related to high ozone concentrations during spring–summer months (Fig. 2a and b), and the other to lower concentrations for autumn–winter months (Fig. 2c and d). Both the Average Linkage and Ward methods suggested quite a similar clustering. Identical results were obtained for winter, spring and autumn groups. For spring clusters, however, slight differences were found. The Ward

Conclusions

Metropolitan area of Seville exhibits notable problems related to ozone episodes as a result of the combination of high solar radiation and temperatures with pollutant emissions, mainly in summer months. Thus, this area is divided into 3 typologies according to hourly ozone concentration in summer: (i) a very high ozone concentration area surrounding the city of Seville, (ii) a high ozone concentration area that corresponds to the city, and (iii) a moderate ozone concentration area located in

Acknowledgments

The authors gratefully acknowledge the support from Project P08-RNM-3989 funded by Consejería de Economía, Innovación, Ciencia y Empleo (Junta de Andalucía). Results obtained from the information supplied by the Spanish Meteorological Agency (AEMET) belonging to Ministerio de Agricultura, Alimentación y Medio Ambiente. We would also like to convey our gratitude to Consejería de Medio Ambiente y Ordenación del Territorio (Junta de Andalucía) for providing us with the data time series.

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