Why are the number of exceedances different between the ASR and the GM CAP air quality data?
The GM Clean Air Plan also monitors NO2, using diffusion tubes. However, the sites where the GM Clean Air Plan monitors air quality are, overall, different to the sites used in the ASR.
Government guidance requires the GM Clean Air Plan to monitor those sites where the GM Clean Air Plan’s “target determination” modelling, predicted illegally high levels of NO2 in 2021.
In 2020, of the GM Clean Air Plan’s 222 monitored diffusion tube locations, 16 locations measured NO2 concentrations exceeding the legal annual average standard of 40 µg/m3. Exceedances were recorded in Manchester, Tameside, Stockport, Bolton and Rochdale. This compares to 129 locations that were measuring concentrations above 40 µg/m3 in 2019.
Both the ASR and GM Clean Air Plan monitoring results demonstrate that air pollution reduced in 2020 as a result of the travel and economic restrictions in place due to the COVID-19 pandemic. However, travel patterns and the associated pollutant emissions returned to near pre-COVID-19 levels towards the end of 2020, and therefore, it is expected these improvements in NO2 will not be sustained through 2021.
The significant improvement in air quality during the lockdown periods does demonstrate that traffic is the primary factor causing exceedance, and that reducing vehicle emissions will lead to improvements in NO2 levels.