Differences between weekend and weekday ozone levels over rural and urban sites in Southern Italy

Abstract

Air quality data from a network of 11 monitoring stations in the Apulia region of southern Italy during the summer of 2005 reveal a high frequency of ozone law limit violations. Since ozone is a secondary pollutant, air quality control strategies aimed at reducing ozone concentration are not immediate. Herein, we analyse weekly changes in concentration levels of ozone (O(3)), nitrogen oxides (NO(x)), carbon monoxide (CO), and volatile organic compounds (VOCs), and evaluate how the differences in primary emissions cause changes in the production of ozone. The comparison between weekend and weekday levels of O(3) and its precursors are direct evidence for the existence of the "ozone weekend effect." This effect was observed at all stations with a considerable variation in the overall ozone magnitude, including both traffic stations and non-traffic stations. Data from VOC measurements at traffic stations primarily indicated elevated levels of benzene, toluene, and xylenes (BTX); all of these substances showed an overall decrease over the weekend. A single station indicated levels of non-methane hydrocarbon (NMHC) and PM10, both of which did not demonstrate any weekly cycle. Analysis of weekly and diurnal cycles of O(3), NO(x), CO, NMHC, and PM10 indicates that higher weekend ozone levels result from a reduction in the emission of nitrogen oxides on weekends in VOC-sensitive regimes. This indicates that a reduction in VOC and NO(x) levels would be more effective than NO(x) reduction alone. Our results underscore the need for improved and more efficient VOC measurements.

Weekend-Weekday Effect Assessment for O3, NOx, CO and PM10 in Andalusia, Spain (2003-2008)

“…5, there was an opposite pattern from that observed for NO-NO 2 -PM 10 . This behaviour has been also obtained in other regions with similar features (Schipa et al, 2009). During weekend nights, the ozone concentrations were higher than on work days, although the differences did not exceed 5 µg/m 3 , with the exception of suburban industrial and rural stations, which presented positive differences or differences near zero.…”

“…Similar ozone increases to measure in other Mediterranean regions (Rigas-Karandino et al, 2005;Schipa et al, 2009) but lower than obtained in big urban areas (Stephens et al, 2008) According to these results, in the case of ozone, there was no weekend effect, independent of type of station (similar criteria applied in Qin et al 2004).…”

“…In this area, the weekend effect has been scarcely studied. The weekly variation has been only treated as a part of more general studies (Riga-Karandinos et al, 2005;Felipe-Sotelo et al, 2006) or analysed in a delimited period of time and area (Jimenez et al, 2005;Schipa et al, 2009).…”

The “Weekend Effect” on Ozone in the Warsaw Conurbation, Poland

“…Analysis of diurnal ozone and NO x behaviour confirms the hypothesis that the most likely cause of higher mean weekend ozone levels is a reduction in ozone suppression due to lower NO x emissions on weekend mornings. The reduction in emissions from industrial/traffic-heavy sectors on Sunday (and to a lesser extent on Saturday) leads to greater reduction in NO x relative to VOC, and thus higher VOC/NO x ratios on weekends [7]. This is an important result, as higher VOC/NO x ratios in VOClimited areas increase the efficiency and rate of ozone formation on weekends [9].…”

“…Environmental agencies have placed considerable emphasis on ozone reduction policies based on reduced vehicle emissions, which are the main anthropogenic sources of ozone precursors. However, research remains complicated by the presence of multiple sources of precursors, the non-linear relationships between ozone and its precursors, and the influence of meteorological and climatological factors on ozone accumulation and transport [7][8][9].…”