6. Measure Ratio
Temporal calculation of ratios was calculated and structured from Figures below. Each figure illustrates the time series of a pollutant. Within the figure, graphs A and C represents the concentrations for summer 2013 and winter 2014 (with lines of background, road, and urban highway), while graphs B and D represents the ratios of road versus background, and urban highway versus road for summer and winter.
As for NO2, the overall concentration of background, roadside, and urban highway stations in summer were measured at 25.12ppb, 43.44ppb, and 44.56ppb, while the mean level in winter were at 40.88ppb, 52.71ppb, and 53.58ppb respectively, which was 62%, 21%, 20% higher than summer. The fluctuation range varied tremendously between day and night due to the photochemical effects with ozone and sunlight that accelerated the increase during the daytime, although the range was greater during summer due to longer sunlight hours. In addition, the distinction of NO2 between seasons and station types were noticeable. In summer, NO2 levels of both road and urban highway stations were consistently 5-20ppb higher than background results, which might be a result of high traffic volume. There was also a difference between stations in winter albeit a small number.
With regard to ratio calculation between station types, a considerable difference was observed between day and night. In summer, ratios of averaged road stations and urban highway stations were 1.78 and 1.83 times higher than background stations; this can be compared to winter ratio at 1.33 and 1.35. As mentioned above, the difference might have been made by photochemical effects during sunlight hours, but more weight is added to traffic volume. This can be proven by the large contrasts of urban highway-background ratio where traffic is heavier during daytime and lightens after peak hours.
- A (Summer. Absolute value)
- B (Summer. Ratio)
- C (Winter. Absolute value)
- D (Winter. Ratio)
- A (Summer. Absolute value)
- B (Summer. Ratio)
- C (Winter. Absolute value)
- D (Winter. Ratio)
- A (Summer. Absolute value)
- B (Summer. Ratio)
- C (Winter. Absolute value)
- D (Winter. Ratio)