Source · Select Committees · Public Accounts Committee
Recommendation 20
20
Acknowledged
Defra and DfT also wrote to us to explain that local monitoring is not directly...
Conclusion
Defra and DfT also wrote to us to explain that local monitoring is not directly fed into Defra’s national model in real time, particularly as many local measurements do not meet the data requirements for inclusion in the national NO2 compliance assessment. Instead, they review the model results against local NO2 assessments and use any discrepancies to prioritise improvements to the national NO2 compliance assessment. They also told us that an uncertainty of around +/-30% is not unusual for a model of this scale and complexity, and that their model meets the uncertainty requirements for assessing compliance with the annual mean NO2 limit value under the Air Quality Standards Regulations.27 However, the NAO highlighted that this is the limit of what is permitted.28 Working with local government
Government Response Summary
The government acknowledges the uncertainty in the national model but states it meets requirements for assessing compliance and that they continue to work with experts to improve it and have set up a new monitoring network that has greatly increased locations where compliance is assessed and has reduced uncertainty.
Government Response
Acknowledged
HM Government
Acknowledged
An uncertainty of around +/-30% is not unusual for a model of this scale and complexity, and assessments have demonstrated that the national model meets the uncertainty requirements for assessing compliance under the AQSR. The government continues to work with external experts to identify and implement further targeted improvements to the national model to ensure it uses the best available evidence and reflects the impact of local measures. The government has also set up a new monitoring network which has greatly increased the number of locations where compliance with NO limits is 2 assessed using measurements. This network is achieving lower levels of uncertainty (<15%) and has more than tripled the number of roadside measurements used in the NO compliance 2 assessment. Since both modelled and measured values contain uncertainties, the government cannot definitively guarantee that all areas of exceedance have been identified. 29