**1. Introduction**

It is widely acknowledged that research for sustainable development has to be context-oriented to reflect the diversity, complexity, and dynamics of the processes involved, as well as their variability between specific problem situations. Moreover, the interests and knowledge of stakeholders involved have to be considered. Sustainability research covers a wide spectrum of socio-ecological challenges, from the over-exploitation of natural resources, for example, to biodiversity loss to climate change adaptation and mitigation. In this approach, we address specific air quality challenges.

Atmospheric aerosol particles originating from the incomplete combustion of fossil fuel or biomass are proven to cause severe health issues. Particulate air pollution is currently one of the world's largest

environmental health risks [1]. There is vast evidence on the negative health effects of each air pollutant, which may have synergistic effects when exposed to a mixture of ambient pollutants. Some of the most prominent health impacts of air pollution are respiratory and cardiovascular diseases, lung cancer, diabetes, and stroke [1–3]. The latest Global Burden of Disease study estimated that 4.9 million premature deaths occurred in 2017 due to exposure to air pollution [4]. Air-pollution-associated adverse health effects create large economic costs through hampered human capital formation [5] and increasing health costs [6]. Apart from negatively affecting health and the economy, absorbing aerosols, such as black carbon, contribute to rising temperatures and lead to regional climate effects [7,8]. These consequences taken together create a growing awareness for the topic of air pollution within sustainability science.

Although poor air quality remains a concern in many countries in the Global North, it poses an even bigger health risk in Asia, particularly among lower- and middle-class income population groups in Southeast Asian countries [1,9]. Compared to countries in the Global North, various low- and middle-income countries in Southeast Asia have experienced rapid urbanization, accompanied by rampant economic and industrial developments. This process comes with the trade-off of air-pollution-related complications and air quality managemen<sup>t</sup> systems are unable to keep up with the challenges [10,11].

One striking example of rapid economic growth and rampant urbanization rates that are accompanied by high levels of air pollution is the Philippines [12]. Metro Manila, the capital region of the Philippines, is composed of 16 cities and one municipality. It is one of the biggest and most densely populated megacities in Southeast Asia, with around 13 million inhabitants [13]. An insufficient public transport system and the accelerating increase in the private vehicular fleet resulted in congested roads being filled with private cars, taxis, old buses, public utility jeepneys (PUJs), and trucks [14]. Jeepneys are a modified version of old military jeeps left behind by Japanese and U.S. soldiers. The jeepney is not only the most affordable option for getting around, it is also iconic, known as the "king of the road" and part of Filipino identity [15]. Equipped with pre-Euro standard diesel engines, PUJs are one of the responsible sources of high concentrations of combustion-generated black carbon (BC) particles, which in turn became a dominant aerosol constituent in the urban atmosphere [16]. There is limited knowledge on the characterization of air pollutants in rapidly urbanizing countries, on its health impacts to the public, as well as on measures contributing to a solution in consideration of the dynamic socio-political institutional frameworks in the country [17]. To address this knowledge gap, a transdisciplinary framework was developed called TAME-BC (i.e., Transdisciplinary Approach to Mitigate Emissions of Black Carbon). This paper introduces the TAME-BC framework in the context of Metro Manila, Philippines, and is intended to be utilized by other projects with similar goals. To do so, the paper starts by providing a brief background on one strand of sustainability research, structuring the research approach. Ensuing, the disciplinary approaches by the various institutes (pillars one to three) involved are explained before bringing them together through the integrative part of the project (pillar four).

### **2. Literature Review: Sustainability Research**

Sustainability research concepts require understanding the interconnected challenges and managing unprecedented problems [18]. The broad base of various scientific approaches for sustainability research can roughly be divided into "descriptive–analytical" and "transformational" approaches [19].

"Descriptive–analytical" approaches are methodologically characterized when systems thinking and/or modeling methods are applied. These methods usually analyze sustainability problems through their past or current frameworks, correlations, and cause–effect dynamics [20–23].

A transformational approach is the second strand in the current state-of-the-art sustainability research. This framework is used for developing evidence-supported solution options for sustainability problems [19,24,25]. Working toward an evidence-based sustainability solution that meets the interests of various stakeholders requires a "transdisciplinary" research approach [26]. Solutions to environmental problems are mostly not just technical fixes or policy procedures [27,28]. Solutions for lowering pollution levels are usually as complex as the problems themselves. Therefore, sustainability research frameworks in the context of air quality managemen<sup>t</sup> require long-term processes that involve real-world experimentation, collective learning, and continuous adaptation [19,29]. Thus, a long-term transdisciplinary approach is a key component of sustainability science when developing evidence-supported pollution mitigation options [30].

The methodological requirements necessary for transdisciplinary sustainability research are transparent, structured, and replicable sequences of steps generating knowledge as ingredients to solution finding [29]. The solutions should be based on a broad understanding of the problem (descriptive–analytical/system analysis) by considering know-how from various sets of stakeholders (scientists, decision-makers, NGOs, practitioners, etc.) [28–30]. They should further work toward a clearly stated sustainability-inspired project goal (normative/target knowledge) and outline change adaptation and transition managemen<sup>t</sup> strategies, i.e., roadmaps for resolving the problem (instructional/transformation knowledge) [31]. Thus, transdisciplinary research needs to apply frameworks combining di fferent types of methods and expertise to generate multidimensional applicable knowledge synergies or co-produced knowledge.

The transformational sustainability research framework, TRANSFORM, synthesizes the key features of the aforementioned frameworks [29]. TRANSFORM integrates transparent, structured, and replicable sequences of steps that generate knowledge, in which researchers


Working along these steps with scientists from various disciplines and non-academic stakeholders allows for co-produced knowledge compared to knowledge produced by scientists only that is then transferred to non-academic stakeholders. The knowledge produced in such a silo is prone to overseeing certain context-specific aspects that might be of relevance to the solution.

### **3. The Metro Manila Air Pollution Case Study**

The cooperation between institutes in Metro Manila and the Leibniz Institute for Tropospheric Research (TROPOS) started in 2014. An Aerosol Instrumentation and Physics Course was held at the University of the Philippines. This course led to the formation of a transnational research collaboration between TROPOS and partners from academia and NGOs in the Philippines called Researchers for Clean Air (RESCueAir). Only one year later, in 2015, the Manila Aerosol Characterization Experiment (MACE 2015) was conducted in Metro Manila to extensively characterize air pollution in three locations in the megacity.

For this purpose, an aerosol measurement container was brought from Germany to the Philippines in 2015, equipped with state-of-the-art aerosol instrumentation, to measure air pollution levels at a roadside in Quezon City, Metro Manila. The measurements focused on the physical-chemical properties of particulate pollution (for further information see Figure 1). A special focus of the measurement campaign was put on quantifying BC particles, which act as a carrier of toxic and carcinogenic components of particulate matter (PM), e.g., polycyclic aromatic hydrocarbons (PAHs) [32]. It was found that the BC levels at the roadside measurement location were up to 50 times higher than in European or North American urban areas [33]. Results also showed that the regulated levels of PM10 from the public transport sector and particularly the BC mass concentrations are up to 70 times higher than in Europe, the USA, and other Asian countries [16]. Results from complementary mobile measurements indicated that the concentration of BC is significantly high along the roads and in areas with very high transport activities [33]. The study further concluded that jeepneys contribute to up to 94% of the overall BC emissions [16]. Based on this finding back in 2015, TAME-BC, the transdisciplinary project launched in 2019, identified jeepneys as the mode of transport under consideration.

**Figure 1.** Map of Metro Manila with the approximate locations of the intensive measurement campaigns during TAME-BC (red triangle) and MACE2015 (black cross) using state-of-the-art aerosol measurement instrumentation.

While the first data were gathered on the characterization of pollutants and marginally on health impacts (during the MACE 2015), less is known about the practices in the transport sector influencing BC emissions. Although technological solutions have been tested in many countries of the Global North, sustainable technological innovations concerning the practices in the transport sector in the tropics are ye<sup>t</sup> to be tested and implemented in Metro Manila. A publication by the Blacksmith Institute and Clean Air Asia [34] has summarized the cost–benefit analysis of different technology alternatives for PUJs (compared to their pre-Euro 4 diesel engines) and recommended several action points. Those action points were discussed with governmen<sup>t</sup> agencies, industries, and transport groups. The recommendation to adopt e-jeepneys in short, fixed routes has been implemented by some local governments, but the rest of the action points were met with financial, technical, and other implementation challenges. The governmen<sup>t</sup> of the Philippines, having recognized the public transport sector as contributing to air pollution, among other shortcomings in the sector, has launched the Public Utility Vehicle Modernization Program (PUVMP). The program introduces a suite of measures to make public transport more sustainable [35]. One of the program components is the phasing out of conventional PUJs to have them replaced with Euro 4 compliant vehicles. As the drivers are expected to incur the costs of new units with only partial support from the government, and most PUJ drivers are part of the low-income sector, mostly without formal working contracts and their benefits, the program is facing public resistance. This discordance necessitates further efforts to understand the institutional implications of proposed solutions if inclusive and integrative sustainable actions are aimed for.

The broadened interest in developing a research project to support solution-oriented knowledge production led to the planning stage for the research project TAME-BC, which focused on a transdisciplinary approach. The novel approach that was launched in 2019 integrates the natural, health, and social sciences in addressing the perennial problem of air pollution in Metro Manila.

The transdisciplinary research setup provides a platform to gain a better understanding of the environmental impacts of BC and how to overcome the negative consequences by finding answers to the following research questions:


The methodology presents how theoretical approaches are translated into scientific practices through an integrated transdisciplinary sustainability research approach. The following sections describe the detailed methods of the various disciplines, as well as the attempt to integrate them toward a solution orientation.
