4.1. GAM vs UK: Boxplot outcomes of NO2
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In summer, the outcome of NO2 concentrations varied between 15 and 45ppb, which was far below the daily standard of 60ppb (the evening of 18th September was the only segment that exceeded the standard). This plots shows some interesting facts. First, the average of GAM was similar or marginally higher than the UK in most days, but the extreme values were more observed in the UK outcomes (I speculate that UK has better estimated NO2 concentration in the CBD). Second, some days have small variations while other days have large variations. Third, cycles change in a 3-day period which was different than the assumption. It is supposed that the the traffic effects of 'high during days' and 'low during nights' is not observed in this plot.
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However, during Winter, there were 8 and 9 days that UK and GAM surpassed the NO2's national standard of 60ppb. The 3-day oscillation of peaks and troughs were also shown in Winter except in the last week of February 2014, which might have met a high pollution episode with stable atmospheric conditions (less sunlight as well). Both methods have consistently shown similar values throughout the whole period.