Long Term Analysis of Ozone Night Peaks in the Portuguese Air Quality Station Network

Monday, 15 December 2014
José M. Castanheira1, Ana C Parracho1, Nelson Barros2, Tânia Fontes3, Márcia P Silva2, Alexandre M Ramos4 and Ana C Carvalho5, (1)University of Aveiro, CESAM & Department of Physics, Aveiro, Portugal, (2)University Fernando Pessoa, Faculty of Science and Technology, Porto, Portugal, (3)University of Aveiro, TEMA, Department of Mechanical Engineering, Aveiro, Portugal, (4)University of Lisbon, Faculty of Sciences, Lisbon, Portugal, (5)New University of Lisbon, Faculty of Science and Technology, Lisbon, Portugal
The gross pattern of the ozone daily cycle in urban areas is similar to that of rural areas, which shows a unimodal variation. However, urban areas can evidence a secondary peak in ozone concentrations during the nighttime, thus presenting a bimodal variation in the daily cycle. Although the occurrence of nocturnal maxima (peaks) has been identified in previous studies, statistics based on long data series have not yet been fully analyzed. The main goal of this communication is to present a study of the daily variation of surface ozone, the frequency of occurrence of nocturnal maxima, their seasonality and their dependence on the type of air quality station. Hourly ozone concentrations collected in 39 background air quality stations during 24 years in Portugal were analyzed. Relationships between the frequency of occurrence of nighttime peaks and the season and the type of air quality station are demonstrated. Using road traffic data, it is suggested that the dependence on the type of air quality station is due to the impact of road traffic emissions in the late afternoon and early morning ozone titration. Moreover, using an automatic weather type classification, relationships between weather types and surface ozone concentrations are also suggested.