Source · Select Committees · Public Accounts Committee
Recommendation 2
2
Accepted
There is a high level of uncertainty in government’s model for assessing pollution levels, which...
Recommendation
There is a high level of uncertainty in government’s model for assessing pollution levels, which may mean that further areas of poor air quality might be missed by the programme. Government uses a national model to identify areas that are likely to be breaching air quality limits, and uses this to direct local authorities to take action. The national model does not directly use the results of monitoring by local authorities; instead, it uses a national network of monitoring stations. The model is regularly updated to take account of differences to local modelling, however government estimates that overall uncertainty in the model remains at the ‘allowable limit’ of +/- 30%. There is no formal margin of tolerance to identify local authorities for inclusion in the programme, and some local authorities are concerned this may result in an unfair situation whereby areas with high levels of NO2 pollution are not required to take action due to the national model not predicting a breach. Recommendation: As part of the Treasury Minute response, the government should set out how it will satisfy itself that all areas in exceedance of pollution limits have been identified and included in the programme, taking into account the high levels of uncertainty associated with the national model.
Government Response Summary
The government states that the best available evidence has been used to identify areas exceeding pollution limits and that the national model meets uncertainty requirements. They will continue to improve the model and have increased the number of monitoring locations. They will consider local authority monitoring data if it meets AQSR requirements.
Government Response
Accepted
HM Government
Accepted
The government agrees with the Committee’s recommendation Recommendation implemented The government is satisfied that the best available evidence that meets the stringent requirements for assessing compliance with the annual mean Nitrogen Dioxide (NO ) limit value under the Air Quality Standards Regulations (2010) (AQSR) has been used to identify areas in exceedance and bring them into the programme. 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 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 assessment. Since both modelled and measured values contain uncertainties, the government cannot definitively guarantee that all areas of exceedance have been identified. Where local authorities’ air quality monitoring identifies a potential NO breach, they can share this evidence with the Joint Air Quality Unit. Whether a locally identified breach should be tackled through the NO programme or through the Local Air Quality Management (LAQM) regime will depend on whether the monitoring data meets the specific siting and data quality requirements of the AQSR.