Worldwide people tend to spend approximately 90% of their time in different indoor environments. Along with the penetration of outside air pollutants, contaminants are produced in indoor environments due to different activities such as heating, cooling, cooking, and emissions from building products and the materials used. As people spend most of their lives in indoor environments, this has a significant influence on human health and productivity. Despite the two decades of indoor air quality (IAQ) research from different perspectives, there is still a lack of comprehensive evaluation of peer-reviewed IAQ studies that specifically covers the relationship between the internal characteristics of different types of building environments with IAQ to help understand the progress and limitations of IAQ research worldwide. Therefore, this review of scientific studies presents a broad spectrum of pollutants identified in both residential and commercial indoor environments, highlighting the trends and gaps in IAQ research. Moreover, analysis of literature data enabled us to assess the different IAQs in buildings located in different countries/regions, thus reflecting the current global scientific understanding of IAQ. This review has the potential to benefit building professionals by establishing indoor air regulations that account for all indoor contaminant sources to create healthy and sustainable building environments.

Urban sprawl and increasing population density in urban centers create the challenge to finding ways of sustainable transportation solutions that preserve the convenience of residents while reducing emissions. Therefore, walkability is a core urban design element because of being advantageous onto three fronts: health, livability, and sustainability. Adopting walkability as urban solution relieves conceptual and practical tensions between the individualistic interests manifested in the desire to own and use private cars, and the need to reduce transportation-based consumption. This review advocates that long-term health benefits from walking and physical activity are the premier incentive to repurpose our cities to be more sustainable and more walking friendly, and spark behavioral change into reducing car dependency for all daily transportations. The review inspects physical elements of the built environment that make the walking trip feasible and desirable, such as connectivity, accessibility, and closeness of destination points, presence of greenness and parks, commercial retail, and proximity to transit hubs and stations. Hence, this review explores a few popular walkability evaluation indices and frameworks that employ subjective, objective, and/or distinctive methods within variant environmental, cultural, and national context. There is no unified universal standardized walkability theory despite the need for rigorous evaluation tools for policy makers and developers. Furthermore, there is a lack of emphasis on air quality and thermal stress while approaching walkability, despite being important elements in the walking experience. Research opportunities in the field of walkability can leverage location tracking from smart devices and identify the interaction patterns of pedestrians with other transportation modes, especially for those with fundamental movement challenges such as wheelchair users.