Abstract
ABSTRACTThe surface ozone time series is analyzed for the seasonal and inter-annual variations and the trend in the following three categories (a) monthly mean (b) 8 hr monthly mean and (c) daily maximum monthly mean measured at 8 (urban/suburban) sites in Portugal for the period 2000–2010. The inter-annual variation of the monthly mean surface ozone time series showed an year to year variation with the highest value in May 2009 (95 µg m–3) at Monte Chaos and the lowest in Jan 2002 (17 µg m–3) at Paio Pires. The trend analysis of (1) original surface ozone time series and of (2) deseasonalized surface ozone time series for all the three data set categories and for all the 8 sites was performed and found to be statistically significant at 6 sites for monthly mean and 8 hr monthly mean and at 5 sites for daily maximum monthly meanusing the non-parametric Mann-Kendall test. The analysis of original surface ozone time series showed a positive trend at 6 out of 8 sites, but the results were not statistically significant for most of the sites due to the presence of the annual cycle masking the actual trend values. However, the analysis of deseasonalized surface ozone time series showed a statistically significant increasing trend at 7 out of 8 sites with high Z values. The positive trends found in the deseasonalized surface ozone time series were in the range 0.44 up to 1.42 µg m–3 year–1 for the monthly mean surface ozone time series (7 stations), 0.33 up to 1.43 µg m–3 year–1 in the case of the 8 hr monthly mean surface ozone time series (7 stations) and 0.66 up to 1.55 µg m–3 year–1 in the daily maximum monthly mean surface ozone time series (6 stations).
Highlights
Surface ozone (O3) is a highly reactive trace gas and an important greenhouse gas (Mickley et al, 2001) which contributes to global warming and climate change (Unger et al, 2006)
The annual cycle dominates in the monthly mean, the 8 hr monthly mean and the daily maximum monthly mean surface O3 time series values at any given location around the globe and the same was observed at all the sites used in this study (Supporting Information SI1-Figs. 1(a), 1(b), 1(c): time series plots for all the 8 sites for each time series respectively)
In the bimodal variation observed in themonthly mean surface O3 time series, the absolute maxima occurs in the spring season and the relative maxima in the summer, while in the bimodal variation observed in the 8 hr monthly mean and in the daily maximum monthly mean surface O3 time series, the relative maxima occurs in the spring and the absolute maxima in the summer
Summary
Surface ozone (O3) is a highly reactive trace gas and an important greenhouse gas (Mickley et al, 2001) which contributes to global warming and climate change (Unger et al, 2006). Increase in emission of O3 precursors such as nitrogen oxides (NOx), volatile organic compounds (VOC’s), carbon monoxide (CO) and non-methane hydrocarbons (NMHCs) (Saito et al, 2002) from traffic and industrial activities lead to increased production of surface O3 over polluted regions (Kulkarni et al, 2010). This is of great importance since O3
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