# Air Quality Effects on Human Health and Approaches for Its Assessment through Microfluidic Chips
## 1 Introduction
This facilitates the development of highly reliable, economical and mass-produced satellites that might also be used for monitoring pollutant sources, such as dust storms or volcanic activity [9]. On the ground, LoC systems offer an unprecedented sensitivity in the assessment of small particle characteristics or the detection of chemicals. For example, hazardous particles in the air, which can originate from pollution sources, can be assessed by the right type of device [10]. Nowadays, it is not uncommon to access the readouts of the closest air monitoring station through a respective online portal. The readouts are determined and immediately provided in real-time (Figure 1) [11]. The air monitoring stations cost from several hundred to tens of thousands of dollars, and are usually affordable for cities with a population of over one hundred thousand people [12]. Conventional 2D cell culture, although of immense value in past research, is strongly limited in recreating tissue-specific parameters, such as pH, \(\mathrm{PO}_{2}\), extracellular matrix composition, or the presence of mechanical forces. Thus, the translation of data gained in conventional cell culture into complex organisms is hampered, a disadvantage that is apparent in many fields, such as regenerative medicine or toxicology. To compensate for these shortcomings, animal experiments are widely used, especially in the risk assessment or testing of chemicals and novel drugs. Yet, the species-specific differences between test animals and humans make a direct translation of results difficult [13; 14]. One possible way to overcome these shortcomings is the use of OoC systems. Here, microfluidic platforms or chips are used to recreate a physiological environment that resembles the specifics of the tissue of interest, and also allows the co-culture of different cell types in 2D or 3D [15]. In addition, the connection of several different organ-models on one platform was proposed, a concept dubbed multi-organor body-on-a-chip. OoC systems, like functional Lung-on-Chip, Heart-on-Chip, Kidney-on-Chip, Liver-on-Chip and other OoCs are readily available, and funding in this area of research is increasing (Table 1) [16]. These developments raise big hopes, as they allow for low-cost testing of drugs and chemicals, while physiochemical and cellular parameters of the tissue of interested can be recreated, therefore increasing the predictive value of the OoC. Recent lung-on-a-chip systems allow for testing airborne particles and substances for their toxicity on various cells in a monolayer or as 3D cell aggregates [17]. One example of such an approach is the smoking small airway-on-a-chip where a device that mimics human smoking is connected to a lung-on-a-chip to induce and investigate pathological phenotypes caused by inhaling cigarette smoke [18]. In this review, we want to provide an overview on air pollutants, including their sources and accompanied health risks due to exposure. Furthermore, the usage of LoC and OoC devices in the context of air quality assessment and health risk investigation will be discussed.