Trends in air quality funding

Outdoor air quality funding

Outdoor air quality funding rebounds strongly in 2024

In 2024, outdoor air quality funding¹ rose to $4.7 billion, up from $3.0 billion in the previous year and approaching the 2022 high of $4.8 billion (see table below). While this increase is a positive short-term signal, year-on-year funding does fluctuate based on the presence of large projects. Tracking annual changes helps identify systemic shifts and priorities, especially as development resources come under increasing pressure.

Outdoor air quality funding held steady at 13% of total air quality funding in the 2020-2024 period, a marginal decrease from 14% in 2019-2023, showing that there has been no structural shift towards explicitly targeting air quality improvements across the funding landscape over the medium term. 

Flows of outdoor air quality funding indicate whether funders are prioritising air quality by explicitly incorporating it into their projects and investments. The data shows that the majority of finance for air quality continues to come as a co-benefit of broader investments targeting other objectives, rather than for projects that explicitly prioritise clean air.

This distinction matters. Making air quality an explicit project objective helps embed it in project design, appraisal and monitoring, including by using indicators against which air quality outcomes can be measured.² Increasing funding that explicitly targets air quality could help convert incidental benefits into intentional, measurable outcomes while strengthening the evidence base for future investment.

Despite strong growth in 2024, outdoor air quality remains at less than 1% of international development funding

Outdoor air quality funding saw year-on-year growth of 58% in 2024, while total international development funding grew by just 4%. As a result, its share in total international development funding rose from 0.6% to 0.9%.

Despite this progress, systemic underfunding persists. Taken over a five-year period from 2020-2024, outdoor air quality’s share of funding has fallen to 0.7%, compared to 0.8% in the previous five-year period of 2019-2023. This low prioritisation represents a missed opportunity in the development agenda, given the extensive health, productivity, and prosperity benefits of addressing air quality.

Funding with air quality co-benefits

Funding with air quality co-benefits falls in 2024, after three years of growth

This drop is concerning, as these flows represent the vast majority of investment in air quality. Funding with air quality co-benefits – i.e., for projects that support but do not explicitly target air quality improvements according to their names or descriptions – fell by around 13% in 2024 (see table below). This category saw its first drop after continuous growth from 2020 to 2023.

Although co-benefit funding is not explicitly targeted toward improving air quality, it still delivers important improvements and makes up the majority of air quality financing (84% in 2024). Despite the decline in 2024, the medium-term trend shows resilience. Funding with air quality co-benefits increased by 11% across the latest five-year rolling periods, from $98.2 billion in 2019–2023 to $108.7 billion in 2020–2024. The 2024 drop dampens the upward trend, and funding in the coming years will be crucial to avoid reversing growth.

Climate-related air quality funding

Climate-related air quality projects, however, continue to account for most air quality funding. In 2024, non-climate-related air quality funding³ increased significantly from $4.4 billion in 2023 to $7.9 billion in 2024 – a short-term signal of greater support for projects that target air quality objectives without being classified as climate-related. By contrast, climate related air quality funding fell from $26.0 billion to $20.8 billion.

Despite this increase, climate-related funding continued to account for the majority of air quality funding. Over five-year rolling totals, the climate-related share of total air quality funding remained constant at 81%. For outdoor air quality funding, the climate-related share declined from 86% in 2019-2023 to 83% in 2020-2024.

In a context of constricting international budgets, funding solutions that simultaneously benefit both air quality and climate can help to make limited resources stretch further and maximise impact.

Total air quality funding

Total air quality funding falls for the first time in five years in 2024, driven by a decline in co-benefit funding

This drop dampens an otherwise upward trend from 2020-2024. Total air quality funding – comprising outdoor air quality and funding with air quality co-benefits – declined by 6% ($1.7 billion) between 2023 and 2024, to $28.7 billion.

Strong growth in total air quality funding in recent years means that the 2024 drop only dented an upward trend. Comparing the two most recent five-year rolling totals, total air quality funding grew by 9% ($10.8 billion) in 2020-2024 compared to 2019-2023 (see table below). However, the year-on-year decline has slowed this positive trajectory and suggests a deceleration of progress on improving air quality.

A small number of large projects – predominantly urban rail and metro – drive funding.

Air quality funding is dominated by the transport sector (see our section on sectors). This partly reflects a tendency in international development finance to favour large-ticket infrastructure projects, as project preparation and other overheads become more economical at scale. This is particularly evident in the transport sector, where multilateral development bank (MDB)-funded transport projects had an average ticket size of $170 million between 2015 and 2022⁴ largely reflecting investment in metro-rail.

As a result, a relatively small number of large transport and infrastructure projects dominated overall air quality funding volumes:

• Ten projects accounted for 53% ($8.4 billion) of total outdoor air quality funding between 2020-2024.⁵ Seven of these projects supported rail and public transport, particularly metro development.
• Some 15% ($16.8 billion) of total investment across 2020-2024 in projects with air quality co-benefits came from just ten projects. Seven of these related to rail development.

Given the tendency for funders to favour large-scale investments, annual funding volumes can fluctuate based on the timing of a small number of large infrastructure investments, meaning that medium-term analysis is important to contextualise year-on-year changes.

Less than 6% of international development funding goes to projects with air quality benefits

The drop in total air quality funding in 2024 drives down its share in international development funding

Total air quality funding accounted for a smaller share of development funding in 2024 (5.8%) compared to 2023 (6.4%). While total air quality funding declined year-on-year, total international development funding grew by 4% from 2023 to 2024. The medium-term trajectory, though, shows decline: year-on-year growth in international development funding slowed from 11% in 2022 to 9% in 2023. In addition, significant cuts to official development assistance (ODA) are expected to impact 2025 figures in next year’s tracking.⁶

Five-year rolling totals show that the share of total air quality funding in international development funding remained constant at 5.6% across 2019-2023 and 2020-2024. This lack of growth is a missed opportunity for air quality to gain ground within the development agenda.

Notes and references

¹Indoor air quality projects are captured in the ‘funding with air quality co-benefits’ category, separately from outdoor interventions, as indoor air quality is already more distinctly targeted and addressed, for example, through clean cooking initiatives and dedicated tracking efforts.

²Clean Air Fund. 2025. Air Quality Toolkit for DFIs.

³Many projects addressing air quality have benefits for climate mitigation, and vice versa. A project’s climate relevance is defined by the reporting institution, with projects tagged for climate relevance when reporting into the OECD Climate-related Development Finance (CRDF) according to whether they have explicit climate objectives. A project’s air quality relevance is defined by the State of Global Air Quality Finance (SOGAQF) keyword taxonomy.

⁴CCFLA. 2023. Accelerating Urban Climate Finance in Low- and Middle- Income Countries.

⁵Projects can span multiple phases, with funding commitments made across different years. For example, tranches for the JICA-funded Metro Manila Subway Project were committed several years apart (JICA, Railway Gazette). For the purposes of this top ten, each project phase is counted as a distinct project.

⁶OECD. 2026. Preliminary 2025 ODA data.