A framework for assessing the contribution of UK local authorities toward compliance with the EU ambient air quality directive

Implementation outcomes of the Ambient Air Quality Directive (AAQD) (2008/50/EC)) are weak across European Union (EU) member states. In the UK, Local Authorities (LAs) must work toward reducing air pollution, however, means of assessing the extent and effectiveness of their contribution are limited. This paper develops a framework to evaluate policies implemented by UK LAs to address air pollution and applies it to Air Quality Action Plans (AQAP) of five cities. It looks at how, and the extent to which, LA air quality policies align with AAQD requirements, thus advancing empirical and academic knowledge on implementation literature surrounding multi-level governance, specifically the policy disconnect between the AAQD and UK Local Air Quality Management (LAQM). The application of the framework shows how LAs can better integrate AQAPs into their LAQM plans to assess, develop, improve and implement their air quality policies on the ground.


Introduction
Exceedances of nitrogen dioxide (NO 2 ) legal limits, primarily from transport pollution, persist across 12 EU member states, including the UK (EEA 2017;Nagl, Schneider and Thielen, 2016).
The implementation of air quality policies is complicated by the multi-level nature of the problem that they aim to tackle. Environmental issues such as air pollution require the cooperation of multiple institutional levels vis-a-vis national legislative and governance structures (Mickwitz, 2003;Gollata and Newig, 2017;Knill and Lenschow, 1998). In this regard, Bondarouk and Mastenbroek (2018) have highlighted the need to better assess the contribution made at local authority (LA) level to achieving EU environmental objectives, and proposed a framework which was subsequently adapted to evaluate the AAQD implementation performance of Dutch municipalities (Bondarouk and Liefferink, 2017). The authors identify three key dimensions for the evaluation: substance; scope; and effort. Their analysis highlights that implementation performance was dependent upon how serious municipalities were about tackling air quality (which in some cases led to over compliance) while also dealing with the challenges presented by the lack of measurable obligations from the AAQD. This paper builds on these contributions to assessing the LAs' role in reducing ambient air pollution, with a focus on the UK. The UK requires new assessment tools specifically tailored to the UK air quality governance structure and legislative approach, and which are directly actionable by officers and practitioners.
In the Netherlands, "municipalities are obliged to implement all measures listed under the National Air Quality Cooperation Programme (NAQCP) otherwise they would have to pay back funding granted by the national authority" (Bondarouk and Liefferink 2017, 738). This implies that AQAPs in the Netherlands are automatically implemented locally. This is not the case in the UK, in part due to the limited responsibility that local authorities have to achieve limit values or objectives (Chatterton et al. 2007; Barnes et al. 2018). Moreover, the UK currently implements two separate sets of regulations in a 'twin-track approach' to air quality management (Barnes et al. 2018); the national UK air quality legislation which is derived from the Environment Act (1995) (Air Quality Strategy (AQS)), and the AAQD (the National Emissions Ceilings (NEC) Directive (2016/2284/EU)). These have different governance approaches and legal requirements. For example, the EU AAQD requires member states to work at the scale of zones and agglomerations, while the national legislation works at the local authority scale (Defra 2018c). This makes determining responsibilities for emissions, particularly those which cross LA boundaries challenging, and further complicates reporting to different authorities according to their respective requirements at each level (Barnes et al. 2018). Attempts to integrate the AAQD into national legislation have failed, and there therefore remains a significant policy disconnect between the two regimes (Barnes et al. 2018).
This paper tackles the following research question: to what extent are LAs contributing toward the achievement of the AAQD? By building on Bondarouk and Liefferink's framework and integrating multidisciplinary insights, the paper develops a supporting tool for decision-makers to use to evaluate UK air quality policies at the local level in a way that considers, and crucially, contributes to, closing the policy disconnect. The empirical application of our framework to the UK allows us to test it in a multi-level governance setting that presents a clearly identifiable and tractable policy disconnect between two different government levels. The contribution of this paper is multidisciplinary, as it brings together insights from EU public policy, air quality management, public health, and transport management, which are critical for the success of air quality policies. Tackling the case of the policy disconnect in the UK air quality domain allows us to address key theoretical issues in the multi-level governance literature, namely coordination failures, mismatches between administrative areas, gaps and asymmetries of information (Allain-Dupr e 2020; Charbit 2020). Furthermore, building our framework on insights from the EU multi-level governance literature enables it to be adapted to analyze air quality policies in other EU multilevel governance systems and policies. Finally, by directly addressing these key challenges, our framework represents a supporting tool for the development of policies that are better aligned and coordinated, thus reducing policy implementation cost, duplication and enabling the delivery of stronger environmental outcomes.
The next section outlines the challenges of implementing EU law and UK air quality policies; it describes the development of a UK-specific assessment framework, and applies it to five UK cities (Bristol, Glasgow, Leeds, Manchester and Newcastle).

AAQD and LAQM in the UK: critical dimensions
Analyzing the implementation of EU environmental law is complex and research in the field has identified various factors that can determine compliance (Knill and Lenschow 1998). For example, multi-level requirements can conflict with more centralized administrative traditions in some member states leading to poor policy outcomes (Gollata and Newig 2017;Leventon 2015, Lenschow, Becker, andMehl 2017;Knill and Lenschow 1998). Also, decision makers may allocate more resources, expertise or stringent interventions into particular policies or directives ( Cavo ski 2017). However, the implementation of environmental policy can also be facilitated by cross-policy linkages (Olowoporoku et al. 2012). For example, climate change and air quality policy, as "they arise from … the same sources and will therefore benefit from many of the same measures; so the combined benefits are substantially greater" (Defra 2010, 3) ( Cavo ski 2017). Equally, the joined-up policy approach of air quality management in Local Transport Plans could also make policy implementation more effective (Olowoporoku et al. 2012). However, the integration of environmental policies, either intra-departmental, cross disciplinary or otherwise, can also come with restrictions such as funding, particularly in terms of air quality policy implementation (Olowoporoku et al. 2012;Cavo ski 2017). A comprehensive review of the EU implementation literature is beyond the scope of this paper; what is relevant for the purposes of this paper is the difference between the legal and practical implementation of EU law (Zhelyazkova, Kaya, and Schrama 2016). Member states may be compliant by following procedures as stipulated by the directive (H eritier 2002;Liefferink, Wiering, and Uitenboogaart 2011), however, they can still fall short of achieving the intended outcome (e.g. LAQM in the UK (Longhurst et al. 2009)) (Leventon 2015). In order to meaningfully assess practical implementation, UK LAs need an assessment tool that goes beyond a dichotomous approach to compliance, that is tailored to the UK context and that contributes to closing the policy disconnect.
In the UK, responsibility for meeting EU limit values is devolved to the national administrations, who together with Defra have produced the UK Air Quality Strategy (AQS) (Defra 2018a; Longhurst et al. 2009). Parallel to this, the 1995 Environment Act defines LA responsibility for local air quality (LAQM), and states that LAs are required to 'work toward' air quality objectives (Defra 2018c; Beattie, Longhurst, and Woodfield 2001;Barnes et al. 2018). If, after a review and assessment process (conveyed in the Annual Status Report [ASR]), air quality objectives are exceeded or not likely to be met, LAs have to declare an Air Quality Management Area (AQMA) and produce an Air Quality Action Plan (AQAP) with details of initiatives to be put in place to meet these objectives (Defra 2016;2017;Longhurst et al. 2006;2016) The UK approach to air quality has evolved from "an exclusively source-control approach" (Longhurst et al. 2009, 76) in the regulation of sulfur dioxide from power stations to combat smog through the Clean Air Acts of 1956 and 1968 "to a complex but integrated, risk management effects-based process of air quality management" (Longhurst et al. 2009, 76) in the form of the AQS today. While air quality management was originally centralized, the Clean Air Acts supported local air pollution control coupled with a centralized national monitoring network. Since then, the collaboration between local and national government is considered the most efficient and precautionary approach in the management of air pollution, as the identification and management of local hotspots is considered best addressed at a local level (LAQM), and other elements of policy, such as fuel and engine quality standards, are addressed nationally (Longhurst et al. 2009;Barnes et al. 2014). While initially considered a success, over the last 21 years, LAQM has been subject to criticism due to the continued failure of the UK to meet both UK and EU NO 2 and PM 10 targets by their 2005 (UK) and 2010 (EU) deadlines Barnes et al. 2018, EEA 2017Andrews 2015). Further, action planning to date has been relatively ineffective (Chatterton et al. 2007;Barnes et al. 2014; with few revocations of AQMAs following the implementation of AQAPs Barnes et al. 2018).
There are many reasons behind the failure to achieve air quality objectives in the UK, spanning from the failure of Euro Standards to reduce general emissions across Europe as quickly as expected and a lack of communication and engagement across departments (e.g. public health, air quality, planning and transport) at different levels of government (Olowoporoku et al. 2012). Local decision-makers find themselves restricted in their abilities to effectively implement air quality policies as a result of uncertainty as to their responsibilities, coupled with a lack of capacity and competing local policies (Barnes et al. 2014;, which are manifestations of key challenges as highlighted by the literature on multi-level governance and its impact on policy outcomes. Further, the uncertainty and assumptions made by DEFRA around emission factors for NO 2 , fleet dynamics, and future projections for the UK's Air Quality Plan (or Clean Air Strategy), raise questions as to its robustness Moorcroft and Dore 2013). From a policy perspective, this failure has been driven primarily by a disconnect between the LAQM and AAQD implementation processes. For example, while the AAQD monitoring requirement stipulates "at least one monitoring station per zone/agglomeration, representing a designated area (m 2 ) where concentrations are highest and there is relevant exposure" (Barnes et al. 2018, 6), for LAQM "there is no legal requirement to monitor … but recommended assessment should be made at the 'worst-case' location representative of relevant exposure" (Barnes et al. 2018, 6). This particular example highlights the difficulties in determining which authority, national or local, has responsibility for the differing ways of approaching the same issue.
Directly engaging with the literature on policy implementation in multi-level governance settings, this paper develops an assessment tool for better integrating and aligning LAQM and AAQD, which can be used by LAs as a guide during the policy development stage and by Defra as a performance assessment tool. Our focus on integrating, within a unified assessment tool, dimensions that are critical for air quality and which operate across different levels of government offers an opportunity for LAs to systematically identify and address coordination issues, mismatches and asymmetries of information, which undermine the achievement of multi-level policy goals.
3. Toward a framework to assess UK local air quality policy implementation performance Bondarouk and Mastenbroek's framework included key aspects against which to assess Dutch cities' performance. These aspects are: for Substance: Objectives and Definitional details; for Scope: Territory (or Application Area), Duration, and Addressees; for Effort: Expertise, Prioritization, Monitoring, Staff, and Budget (or Funding).
We depart from this framework in three ways: first, the peculiarity of the UK context forces us to design an assessment tool that is robust and flexible enough to be applied to both the LAQM and AAQD regime and provide us with an overall measure of performance from a multi-level perspective. In so doing, we also specifically assess the management scale adopted by each city. This is important as the original LAQM approach designed to tackle very localized 'pollution hotspots' has been inadequate (Woodfield et al. 2002). This has led some cities to try city or regional scale AQMAs to address air quality issues more holistically, which is more likely to address the transboundary nature of some pollutants and polluting activities (BCC [Bristol City Council] 2018; GMCA 2016; Woodfield et al. 2003Woodfield et al. , 2006. This constitutes a step forward toward closing the policy gap discussed above. Second, we adopt a more holistic and integrated perspective by extending the scope of our assessment to include other substantive policy domains (local public health policies, transport policies, planning and development and energy use policies) which are drivers for effective air quality management and which will be discussed in more detail. Third, the Framework we propose allows a critical assessment of both the formal implementation of the AQAP, as well as outcomes with reference to air quality targets.
The overall structure of our framework (hereafter known as The Bridging Framework) consists of three sections -Context, Output and Outcome.

Context
This section pertains to the circumstances around the process of LAQM and the production of AQAPs in each city. It concentrates on changes in policy and attitudes toward air quality, as well as obtaining information on the development of LAQM strategy over time. For example, knowledge of the policy successes or failures around AQAP integration into Local Transport Plans (LTP) (Olowoporoku et al. 2011), or changes in number and size of AQMA(s) (Woodfield et al. 2003).
This enables decision makers to better understand the circumstances (politically, economically, etc.) under which these AQAPs were produced and therefore how they compare with others produced at different times. It also helps inform the development of policy within the city context. Further, contextualizing policy by placing it within another policy area, i.e. transport, potentially improves understanding of the problem and thus facilitates implementation (Olowoporoku et al. 2010).
The 'context' section includes three aspects requiring information on the source document type and its date, the current number of AQMAs in the city, and past evidence of change.

Output
The Bridging Framework assesses the AQAP as a whole and the measures separately. Changes made include clarifying the scoring system and definitions, the addition of measures relevant to air quality as informed by the literature e.g. public health, and clearly distinguishes the legal stipulations of the AAQD and LAQM. The fundamental structure and scoring system remain the same as that of Bondarouk and Liefferink's (2018) framework.
In the UK, the method by which AQAP measures are implemented is at the discretion of the local authority (Defra 2016). Our approach accommodates this leeway, attributed by article 23 of the AAQD, allowing for additional measures to be scored even if not explicitly listed in the Bridging Framework. A comments column is also supplied for explanation as required. When measures are developed, as in the case of transport, scores are broken down to give more information for analysis.
Where limited information is supplied in AQAPs e.g. around staff and funding, these aspects are applied only to the assessment of the AQAP as a whole. Further, new aspects are added to this assessment which aim to evaluate elements of overarching LAQM and AAQD polices, addressing the relevant policy disconnects outlined by Barnes et al. (2018). They include measures such as policy tools, equipment specifications (e.g. monitor types), and other recommendations or stipulations surrounding LAQM such as interdepartmental cooperation (Barnes et al. 2018;Olowoporoku et al. 2012). This ensures appropriate evaluation of AQAP content in light of the policy requirements of LAQM and the AAQD.
Along with transport measures, the literature points to extra measures required for evaluation (Naik et al. 2017). Specifically, public health (Brunt et al. 2016;Cannibal and Lemon 2000), planning and development (Naik et al. 2017;Defra 2016), and energy use and production (Jonsson and Hillring 2006;Naik et al. 2017;Defra 2018b). These have been added to the Bridging Framework: Public Health Public health policy is a significant dimension when tackling air quality. A recent death and associated hospital admissions bear a striking association between spikes in air pollution and those admissions (Osborne 2018). Yet, there is still a disconnect between LAQM and public health policy demonstrated by the lack of obligatory health cost assessments in UK air quality policy requirements (Brunt et al. 2016;Defra 2017). However, an integrated assessment of costs of measures and health cost savings are considered a sustainable solution (Miranda et al. 2016) and health impact assessments are being integrated into development plans (WYCA 2015; Defra 2018c).
Transport The literature clearly evidences that it is primarily through transport that NO 2 levels across member states are continually exceeded (EEA 2017). And is thus a key focus in air quality literature. The Bridging Framework focuses predominantly on Transport on this basis (Bondarouk and Liefferink 2017).
Planning and development The Planning and Development measures assess the existence of technical guidance documents showing alignment of local air quality policy with, for example, the National Planning Policy Framework (NPPF) (Defra 2016). These should provide short term action plans for construction projects (Lewis, Shan and Hazzard 2015). Opportunities to assess the implementation of Clean Air Zones and green infrastructure are also included (Naik et al. 2017;Abhijith et al. 2017;Barnes et al. 2018).
Energy use One of the main areas of focus of the new AQS 2018, was toward adopting the WHO standards for particulates (PM2.5) caused by the burning of biofuels as well as NO 2 derived from natural gas domestic central heating boilers, wood burners or power stations (Simkins 2018;Defra 2018b). Energy use and production measures assess the acknowledgement of other pollutants and sources, mitigative actions (e.g. Lo, Norton and Mannis 2001) and integration into climate change policy (Jaramillo and Muller 2016;Ahlers 2016). Their inclusion acknowledges the trans-boundary nature of air pollution thus paving a potential link to policies such as Environmental Permitting Regulations and the Industrial Emissions Directive (GMCA 2016).
These measures reflect the current political, environmental and academic conversations around air quality, reflecting where LAQM needs updating (e.g. Brunt et al. 2016) to sustainably tackle air pollution. These policy domains are assessed in the Bridging Framework.

Scores
Each AQAP measures score is systemized as a score 'out of 100'. Total Output scores are also systemized in this way. This enables easy interpretation and comparability across cities, within their AQAPs, and in relation to the set standard of the Bridging Framework itself.

Outcome
Bondarouk and Liefferink (2017) define policy outcome in terms of air quality improvement. However, the direct outcome of AQAPs is the implementation of its measures (Pohjola et al. 2013;Mickwitz 2003). Both definitions are considered here. This gives insight as to AQAP purpose along with actual deliverable measures, with an eye on any causal relationship between the implementation of air quality measures and an improvement in air quality or even the achievement of AQ objectives.
Additionally, AQAP effectiveness is restricted by the limited policy obligations of LAs (Barnes et al. 2018). If AQAP measures, such as the introduction of a new bus route, are implemented, this can render, in principle, the AQAP a success. However, despite this, objectives and limit values may still be unattained (Barnes et al. 2018). Therefore, AQAPs could be considered an underused resource restricted by UK policy requirements even though their main function is only "to improve air quality in an AQMA" (NSCA 2000, 9). However, in the case of this paper they best reflect the implementation of both EU and UK air quality policy at a local level and are integral to LAQM (Bondarouk and Liefferink 2017).

Application, measures and scoring
For the AQAP as a whole, selected elements of the documents are scored against the aspects, including pollution sources and modes, and reporting frequency. For example, 'Objectives' measure if national air quality requirements are being pursued (Bondarouk and Liefferink 2017). Each aspect of the AQAP assessed is scored to a maximum of three points (see Table 1).
Equally, AQAP measures are scored to a maximum of three points (a self-defined scoring system). However, scores are made according to the quality of the AQAP measure in relation to the aspect stipulations for the equivalent framework measure. For example, under the Bridging Framework's bicycle policy measure, specific definitional details (aspect stipulations) are given for bicycle parking (e.g. free or indoor parking). The score reflects the extent to which the AQAP measure on bicycle parking relates to those stipulations (e.g. 1 definitional detail scores 1 point; 2-3, 2 points; 4-5, 3 points). A high score would be attained if the AQAP (or supporting documents) details information on various initiatives surrounding bicycle parking (for example free and secure parking, provisions for demand, and signage for parking). A low score would reflect limited information in the AQAP or supporting documentation, suggesting that these initiatives have not been implemented or that the plan is lacking detail. AQAP measures on bicycle parking are also assessed under 'Territory' and 'Duration' aspects and are scored similarly (see Table 1).
The scores are summed to indicate a total score for the measure. Aspect scores for that measure are also totalled. Finally, total measures scores and aspect scores (which will be the same) for all the measures in the AQAP are systemized and presented. Equally, when applied to several cities, a comparison can be made between cities' AQAPs regarding both aspects and measures (see Table 2) (Bondarouk and Liefferink 2017).

Identification of case studies and data analysis
The Bridging Framework is designed and tested in relation to air quality policy and practice in five UK cities. The cities used for the application of the bridging framework are five of the six UK Core Cities, which are geographically similar in size, face similar air quality challenges (i.e. the source of the objective exceedances in each city is traffic), and have similar-sized economies (Core Cities 2017). They are Bristol, Glasgow 1 , Leeds, Manchester and Newcastle. The Bridging Framework is used to assess the following documents: Air Quality Action Plans (AQAP), Emissions Strategies, Local Transport Plans (LTP) (as assessed with comparable documents in the Netherlands by Bondarouk and Liefferink 2017)  The Bridging framework is designed to enable a deductive quantitative content analysis of the 'raw data' as listed above. This method is designed to measure and interpret data collected that allows judgment of implementation performance of UK cities (Schrier 2012;Bondarouk and Mastenbroek 2018). Table 2 summarizes the results of the implementation performance assessment of the five UK city AQAPs. They detail where a city's policies may be effective (or not), in what area, and their respective progress toward improved local air quality.

Geographical
Scope of plan Regional (3), City level (2), local area (1) 3 AQAP as a whole total Score (exemplar) 8  From the top, the Context section shows the AQAP type, history, and the number of AQMA's in the city. This is followed by the Output assessment scores systemized into percentages so as to present a clear comparison between the AQAP implementation performance scores, both within each city AQAP and across all five cities. Supporting information Appendix A gives the breakdown of the AQAP Output scores and Context section. Finally, Outcome shows direct results which indicates progress made, at the time of writing, in policy action (date of ASR and Reported implementations), changes in air quality in the cities (Resulting air quality change, AQMA revocations/creations) and changes in NO 2 value against target levels.

Implementation performance of UK cities
The results show both similarities and variations in implementation performance of AQAPs across the five UK cities. There are a variety of scales at which cities' have produced their AQAPs; a very local scale, e.g. Newcastle, and a regional scale, e.g. Leeds. Other cities have chosen to integrate their plans within other policies, e.g. West of England Partnership's LTP. Both Transport Measures and the Scope dimension are the highest scoring. Other than this, no other correlation is made, and each city is unique in its scores. Finally, the overall highest-scoring city is Manchester and the lowest-scoring is Newcastle, which is not necessarily reflected in the outcome results.

Analysis and discussion
By developing a policy-informed, country-specific, integrated and systemized scoring system, this paper contributes to overcome the air quality policy disconnect between LAQM and the AAQD that exists in the UK, and in so doing, contributes to implementation literature on multi-level systems. This analysis highlights how the Bridging Framework can be used to analyze AQAPs implementation performance across an array of aspects. For example, it reflects areas of priority for LAs, and fundamentally where improvement is needed. It also enables a detailed exploration of individual cities' air quality circumstances. Finally, this Bridging Framework allows for the collation of relevant policy documents, such as ASRs, which further helps to contextualize scores. However, the application of the framework can only offer a snapshot evaluation of performance that highlights areas for integration and supports policymakers in identifying existing issues; our analysis does not explore the underlying causal mechanisms that led to these scores. Consideration of causal factors and historical trajectories would require a more in-depth within-case investigation which is beyond the scope of this paper The breakdown of the AQAP scores provides insight into the possible factors contributing to AQAP implementation performance. For example, Manchester and Bristol have high funding scores, demonstrating greater financial potential for implementation. Manchester scores comparatively higher in Monitoring which could support a greater adherence to LAQM and AAQD policy stipulations. In general, across the cities, the lowest-scoring aspect is 'staff allocated' to the implementation of the AQAP, demonstrating a low level of relevant technically-trained human resource dedicated to air quality, irrespective of city size. However, expertise is generally well reported on, implying a good record of cross and intra-departmental cooperation in the creation of AQAPs. Scores show room for improvement across all cities' AQAPs.
The application of the framework elicited contextual information for deriving substantive comparative insights into each city's AQAP. Each city has taken a different approach to LAQM in terms of the scale at which the AQAP has been written. For example, Leeds AQAP is part of the wider West Yorkshire Low Emission Strategy (WYLES), a collaboration of several LAs across the county of West Yorkshire, and scores higher compared to Newcastle's more localized approach to each AQMA hotspot. Whilst these LAs are complying with the formal terms of LAQM, some are adopting a broader and more integrated approach than others (Bondarouk and Liefferink 2017).
Comparatively, the low AQAP scores of Glasgow's AQAP point to limited resources, in funding and expertise, available to tackle air pollution, and the relatively limited implementation area. This is reflected in the age and scale of its AQAP, which, compared to those of the other cities, is the oldest and very localized. However, Glasgow has met its legal obligations to comply with both AAQD and LAQM, but this does not translate into practical changes in air quality on the ground. This is true for all the AQAP's assessed, as none of the cities have met air quality objectives (H eritier 2002;Liefferink, Wiering and Uitenboogaart, 2011;Leventon 2015;Longhurst et al. 2009).
Bristol (and to a greater extent Leeds), as well as taking a spatially strategic approach in creating a West of England Partnership with Bath, built upon their AQAP strategy by integrating air quality with their Local Transport Plan. The high scores demonstrate the success of joined up policy (Olowoporoku et al. 2012). However, Bristol's AQAP does less to address Planning and Development and omits entirely Energy Use and Production. For the latter, this reflects the differing levels of government at which policy responsibilities remain, and the resulting lack of responsibility at a local level (Olowoporoku et al. 2012;Knill and Lenschow 1998).
We have also contributed to AQ policy development by identifying the need to consistently integrate key policies (transport, health etc.) into the AQAP. For example, Energy Use and Production is not considered to be within the current scope of most cities' AQAPs, reflecting the current policy and technical guidance which focuses primarily on Transport, and Planning and Building Regulations (Defra 2016). However, it has been updated to take a more holistic approach (Defra 2018c). Accordingly, transport policy is prioritized with Bristol, Manchester and Newcastle scoring comparatively highly. In general, measures scores are low, yet health measures are acknowledged, particularly relating to NO 2 and PM.
However, both Glasgow and Leeds do report on Energy Use and Production and Planning and Development. In the case of Leeds's AQAP, as a subsidiary of the WYLES, it further reflects the relevance of reporting on these measures due to the plans in (West) Yorkshire to install fracking power stations (WYCA 2015;Vaughan, 2017). Likewise, Glasgow's AQAP addresses boiler emissions, reflecting an incorporation of national policy (Glasgow City Council 2009;AECOM 2018). Thus, the results show where some cities' policies incorporate decisions made at different tiers of governance.
Regarding Substance, Scope, and Effort, the general mid-to-low scores could reflect the level of responsibility that local authorities have in pursuing air quality targets. These, in particular, relate to Substance where the definitional details show limited research into mitigative policy measures. Scope, contrarily, shows that generally all AQAPs address the appropriate timescale, area and, social group(s). However, Effort shows a considerable lacking across the board, with scores below 50. It reflects the current policy situation where resources are not allocated sufficiently due to lack of legal obligation (Barnes et al. 2018, Brunt et al. 2016. While efforts to create effective AQAPs and implement them are demonstrated across the Bridging Framework scores, fundamentally, air quality objectives and limit values have not been met. Even where cities (i.e. Glasgow) have reduced the size of their AQMA(s) or reported revocations, continued declarations are made and the challenge of reducing levels of NO 2 is clearly shown by the differences between NO 2 and limit value. However, four out of the five cities' ASRs reported an improvement in air quality. This shows that current AQAPs are working to an extent, however, they could be improved to better fulfill their designated task.
By identifying areas of poor performance through the output scores, the Bridging Framework highlights the areas in which LAs and higher levels of government could better align their contributions to the AQAP's objectives. This is on the assumption that the AQAP measures are driving this improvement (not external drivers which are not influenced by LAs, such as improvements in vehicle technologies). Currently disaggregating this influence is a challenge, but with effective targeted measurements this is a feasible approach to assessing the impact of many interventions.
The Context and Outcome sections added to the Bridging Framework work to consolidate the alignment of the AAQD and LAQM and frame the Output section in this context. Equally, extra measures added align the Bridging Framework with current literature, and the systematized scoring system makes the results more meaningful. The new measures secure the Bridging Framework as a relevant policy tool for current social, economic and political circumstances. They provide relevant criteria for practitioners to make an informed assessment of their cities' AQ scenario and compare them against others. This could influence further efforts for action (Brunt et al. 2016;Cannibal and Lemon 2000).
Additionally, the systemization of scores make interpretation of the results easier as they deliver a comprehensive idea of implementation output performance of AQAPs relative to the Bridging Framework total scores (the 'standard') and a comparison amongst cities. As a result, LAs can approach the scoring either collectively or competitively which can help them develop better AQAPs. Further, the breakdown of scores enables policy makers to explore a particular area, category, or policy, to focus on, either for improvement or development. The results not only give general information on the (quality of the) contents of the AQAP but also give information beyond a comparison against other AQAPs.
The function of the Bridging Framework is to assess the performance of AQAPs and, in so doing, aligns both the AQS and AAQD in order to close the policy gap between them. Our paper therefore contributes to the literature on multi-level governance and multi-level policy implementation. It explores the consequences of multilevel governance on a specific policy area (Kleider 2020) and provides a tool that directly tackles key multi-level governance challenges such as coordination issues, mismatches and asymmetries of information. Additionally, it supports measures and aspects which reflect both policies and concentrates on where they are both practically implementedat a local level (Barnes et al. 2018;Bondarouk and Liefferink 2017). As a result, and considering the continued non-compliance of the cities' AQAPs, the alignment of the AAQD and LAQM in the Bridging Framework will lead to better aligned policies, thus supporting LAs with their LAQM streamlining processes, thus helping to close the policy gap and produce stronger environmental policy outcomes. This also addresses the "flawed subsidiarity and devolved responsibilities" (Barnes et al. 2014 660) causing the inefficiencies in air quality management and helps focus support on LAs to have the powers to competently manage air quality and positively contribute to the achievement of limit values (Barnes et al. 2014;. The applicability of our framework is not exclusive to the UK context and, as we explained, it can be adapted to analyze air quality policies in the context of other multi-level governance systems. Nonetheless, while the Bridging Framework assesses the implementation performance of cities' AQAPs it could be considered inflexible in relation to its ability to assess air quality policy at different scales, i.e. small towns, or regions. This could possibly be considered a function of the (in)consistent availability of air quality policies at these scales e.g. West Yorkshire Low Emissions Strategy vs Newcastle's 'hotspot' AQAP. On the other hand, as AQAPs are drawn up predominantly at the scale of LAs, if smaller-scale areas did not have an AQMA, an AQAP would not be available to assess. Therefore, it could be argued that the application of the Bridging Framework is restricted by the availability of policy.
The limited availability and varied content of AQAPs for cities, was a considerable limit to the extent of this study. While ASRs were readily available it was challenging to find workable documents from LA websites. Also, AQAP content is discretionary to the LA, thus the interpretation of the practitioner undertaking the assessment of the AQAP may be subjective.
The Bridging Framework currently limits its scope of assessment of Outcome to just NO 2 target values and objectives and therefore requires inclusion of all pollutants listed in the guidance documents (e.g. SO 2 , PM10, PM2.5) to evidence the declaration of all AQMAs. And more information about the nature of AQMAs is required in the Context section, e.g. size and pollutant. Also, currently the existence of the Outcome section, as directed by the literature on LAQM (DEFRA 2016), implies a causal relationship between AQAP outputs and improvement of air quality or even the meeting of objectives and limit values. While there is room for this to be researched, current data does not enable accurate assessment to support this relationship (e.g. Schoen 2018).
The Bridging Framework's application to a larger cohort of cities in the UK is needed in order to further critically evaluate its merits, with a possible extension to other member states. It can be used to further evaluate the general state of LAQM in the UK and the approaches and resources allocated to this endeavor. More research is also required around the causal mechanisms behind the adoption of different AQAP approaches in each case and on the new measures and innovative approaches to tackling air pollution at a local level (Brunt et al. 2016).

Conclusion
This paper presented a directly actionable tool for LAs to assess the implementation of the AAQD and UK national air quality policy within their AQAPs. By doing so it contributes to reducing the policy disconnect that exists between these two policies and contributes to implementation literature in the context of multilevel systems.
This new tool assesses AQAPs and guides development of UK local air quality policy. It assesses the extent to which AQAPs comply with air quality policy, as well as helping to ensure that they do. It serves as a guide and standard for LAs to develop their AQAP content and measures, encouraging focus toward the achievement of air quality objectives and limit values, and thus renders the AQAP a useful policy document. It is easily replicated in other UK cities and it is useful both in application to a single city AQAP, or many, in order to compare performance within or amongst different cities' AQAPs. The Bridging framework can also be expanded to include other dimensions, giving local authorities flexibility in how they want to assess their AQAPs.
Following Brexit and the UK departure from the EU, the UK is no longer under international obligation to comply with the AAQD. Nevertheless, all existing EU legislation was transposed into national legislation, so the air quality regime as set up by the AAQD is still in place. This means that, at the time of writing, the UK law on air pollution remains unchanged. Should limits and objectives change in the future this Bridging Framework will remain adoptable and relevant as it assesses the implementation of solutions as opposed to these specific limits.
As is the case with most environmental problems that do not fall within the limits of well-defined administrative boundaries, tackling air pollution will require some degree of cooperation and involvement between multiple levels of government. As demonstrated in this paper, tools that help policymakers to conduct more integrated assessments of contexts, outputs and outcomes can help to address this challenge. Notes 1. Scotland, is a devolved administration, but still adheres to the UK AQS and LAQM; therefore Glasgow's AQAP will be similar to, and can be used with, the other case studies. However, for clarity, the objectives are set out in the Air Quality (

Disclosure statement
No potential conflict of interest was reported by the author(s).

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