Surface Ozone Pollution: Trends, Meteorological Influences, and Chemical Precursors in Portugal

Rafaela C. V. Silva,José C. M. Pires

doi:10.3390/su14042383

Abstract

Surface ozone (O3) is a secondary air pollutant, harmful to human health and vegetation. To provide a long-term study of O3 concentrations in Portugal (study period: 2009–2019), a statistical analysis of ozone trends in rural stations (where the highest concentrations can be found) was first performed. Additionally, the effect of nitrogen oxides (NOx) and meteorological variables on O3 concentrations were evaluated in different environments in northern Portugal. A decreasing trend of O3 concentrations was observed in almost all monitoring stations. However, several exceedances to the standard values legislated for human health and vegetation protection were recorded. Daily and seasonal O3 profiles showed high concentrations in the afternoon and summer (for all inland rural stations) or spring (for Portuguese islands). The high number of groups obtained from the cluster analysis showed the difference of ozone behaviour amongst the existent rural stations, highlighting the effectiveness of the current geographical distribution of monitoring stations. Stronger correlations between O3, NO, and NO2 were detected at the urban site, indicating that the O3 concentration was more NOx-sensitive in urban environments. Solar radiation showed a higher correlation with O3 concentration regarding the meteorological influence. The wind and pollutants transport must also be considered in air quality studies. The presented results enable the definition of air quality policies to prevent and/or mitigate unfavourable outcomes from O3 pollution.

Highlights

With the constant increase of air pollutants emissions since the Industrial Revolution, an increase of ozone (O3 ) near the Earth’s surface has been observed [1,2,3]
To complete the study area with more recent data and improve O3 trends’ understanding in Portugal, this study aims to (i) determine the evolution of O3 levels in Portuguese rural stations, focusing on exceedances to legally imposed levels for human and vegetation protection; (ii) compare the relationship between the O3 concentrations and one of its precursors (NOx ) for different environments; and (iii) evaluate the effect of meteorological conditions in ozone concentrations
The highest annual average O3 concentrations were achieved at the DN, CR, SN, FA, FM, and ML sites

Summary

Introduction

With the constant increase of air pollutants emissions since the Industrial Revolution, an increase of ozone (O3 ) near the Earth’s surface has been observed [1,2,3]. This pollutant is a powerful oxidant, affecting human health by causing respiratory and cardiovascular diseases [4]. It affects vegetation and ecosystems, leading to crop yield and biodiversity losses [5,6].

Objectives

Methods

Results

Conclusion