Time series plots can be considered as being the ‘bread and butter’ of air pollution analysis. They are useful for visualising long term trends in pollution levels, thereby enabling the evaluation of control measures and highlighting areas for improvement.
An example of this is in visualising changes in the increments in particulate matter (PM) concentrations over regional background levels at roadside and urban background sites in London:
This plot shows general declines in PM levels at Marylebone Road, where levels have long been problematic. This suggests that policies to reduce road traffic emissions at this site have had some degree of success.
Carbon monoxide (CO) is another air pollutant for which reductions in road traffic emissions have been achieved.
The UK’s national emissions inventory shows a large reduction in the contribution of road traffic to overall CO emissions, likely attributable to improvements in catalytic converters. This data is in accordance with a time series plot for Marylebone Road. The graph also shows concentrations of NOx, another air pollutant associated with road traffic:
It shows that similar reductions in NOx concentrations have not been achieved. Hourly measured NOx concentrations show the continued occurrence of excessively high levels: