# A Review of Indoor Air Quality in Social Housing Across Low- and Middle-Income Countries
## 2 Materials and Methods  
The methodology of this scoping review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA-ScR) guidelines [28] and was aimed at conducting a detailed literature review to describe the IAQ, critically assess various research methodologies and identify existing gaps in IAQ research across social housing in developing countries. This review assumes that IAQ challenges in social housing are closely linked to socio-economic disparities, technical constraints, and infrastructural challenges. Residents of social housing are often exposed to higher pollutant levels due to inadequate ventilation, the use of low-cost materials, and behavioral practices such as indoor smoking or reliance on solid fuels [7; 18; 19; 27]. These assumptions formed the foundation for the review. Therefore, there is a need to explore diverse methodological approaches and regional variations in IAQ outcomes to address health inequalities in social housing across developing regions.  
A literature search was conducted across several databases, including SCOPUS, Web of Science, ScienceDirect, Google Scholar, and the University of Liverpool's (UoL) Library, covering publications from 2000 to 2024. Search strings were chosen based on the key terms relevant to the research topic. Boolean operators and database-specific field tags were used to ensure consistent and comprehensive search. The complete search strings for each database are provided in Table S1 in the Supplementary Materials.  
Google Scholar is known for its broader indexing of grey literature and diverse publication types and was included to capture studies not indexed in traditional peer-reviewed databases [29]. The UoL's library was used to access institutional subscriptions and complement the database searches. The overlap between Scopus and ScienceDirect was noted but deemed necessary to ensure no key studies were missed. The time period of 2000 to 2024 was chosen to reflect current trends in air quality studies and policy frameworks, as well as advancements in research methodologies and findings. The search strategy was designed to be inclusive, focusing on studies conducted in developing countries, published in English and investigating IAQ without limiting the type of pollutants affecting populations living in social housing, ensuring relevance to the lived experiences of these communities. Table 1 shows the search parameters and eligibility criteria used in the review. The quality of the included studies was assessed using the 2018 version of the Mixed Methods Appraisal Tool (MMAT) [30]. This tool is specifically designed for systematic mixed studies reviews and evaluates five categories of study designs: qualitative research, randomized controlled trials, non-randomized studies, quantitative descriptive studies, and mixed-methods studies. Each included study was systematically appraised against criteria specific to its design, categorizing each study based on compliance with MMAT criteria. Responses were captured as \"Yes\", \"No\", or \"Can't tell\", with explanatory comments where applicable.  
To provide an in-depth analysis of IAQ problems in social housing across LMICs, the review methodology includes a wide range of exposure assessment methods, from monitoring and modeling of pollutant concentrations to self-reported exposure. This broad approach emphasizes the importance of diversity in research methodologies to accurately characterize differences in air quality within social housing. The results of the literature search are categorized to allow for a more focused examination of the studies, contributing to a better understanding of the specific issues and potential interventions to improve air quality and the well-being of social housing residents in developing countries.  
Figure 1 shows a review process where 3220 records were identified through database searches, including 23 duplicates that were found and removed. An additional 3128 studies