Defra and DfT wrote to us to provide a breakdown of funding through the Joint Air Quality Unit and the Air Quality & Industrial Emissions programme. They also provided a summary of cross-government initiatives that affect air quality; these include work by Defra and DfT, as well as the Department for Business, Energy and Industrial Strategy, the Department for Levelling Up, Housing and Communities, and the Department of Health and Social Care. They explained that while Defra attempts to anticipate and model what the long-term reductions in air pollutants as a result of other department’s policies and initiatives may be, their estimates tend to be subject to uncertainty because it is difficult to predict the level levels of uptake, and other factors that will influence how pollution is reduced in practice. They told us that, given how difficult it can be to determine the precise air pollution reductions associated with net zero policies and other important programmes 36 Q 54 37 C&AG’s Report, para 4 38 C&AG’s Report, para 1.16 39 Q 33 40 C&AG’s Report, para 1.18 41 Committee of Public Accounts, Achieving Net Zero: Follow up, Forty-First Report of Session 2021–22, HC 642, 2 March 2022 42 LAQ0004 Tackling local air quality breaches 13 such as active travel, it would be consequently challenging to assign any meaningful estimates of public expenditure on each component of action that results in air pollution emission reductions. They agree that it is important to have robust procedures in place to ensure they are accountable for how money is spent on programmes in each Department, but believe it would not be proportionate to maintain ongoing detailed tracking of the air quality components of policies affecting air pollution across government, especially if the resulting estimates were subject to uncertainties. They told us that their priority is to ensure that their respective policies dovetail to secure multiple benefits, and to estimate the real-world outcomes and bene