I have a time series which contains monthly readings for air pollution in a city. The seasonality from this time series has been removed.
Given two date ranges, for example Jan-Aug 2008 and Jan-Aug 2009, I want to perform a hypothesis test, which tests the claim that the amount of pollution from March-Dec 2009 is no higher than the amount of pollution from March-Dec 2008.
I'm new to time series analysis and have tried to determine the best way of performing this test, but to be honest I'm not sure where to look. I was thinking t-test, but the sample sizes are quite small so I don't know if it can be used? I also was considering using the Wilcoxon Ranked Sum, but I'm unsure if this is suitable.
Could someone suggest what test, those mentioned or any others, would be most appropriate for testing this hypothesis?
(Oh and my preferred statistical software environment is R, just in case you want to link to any packages)