Characterization of airborne and respiratory particles in indoor environments

The understanding of the relationship between human health and indoor air quality (IAQ) is a never-ending challenge. For decades the main design parameters of efficient buildings were the energy efficiency and, in case, the protection from outdoor pollutants whereas the possible health treat of indoor sources was mostly underestimated. In fact, building occupants are not properly aware of the indoor air quality, of their exposure to pollutants or pathogens and, consequently, of how much they contribute to reducing the indoor air quality through their habits and activities. In addition, modern lifestyles pushed people to spend most of time in indoor microenvironments respect to outdoor ones, and consequently expose them to high pollutant concentrations. Outdoor pollutants are affected by physical and chemical processes, driven by complex meteorology and photochemistry. In contrast, indoor ones are a function of outdoor pollutants, indoor source strength, removal and deposition rate within the structure, indoor mixing, and chemical reaction. All these factors make the study of indoor environment more than challenging, and worthy of attention. Airborne particles represent one of the main pollutants negatively affecting the IAQ, ranging in size from nanometers to millimeters. They can be generated by different indoor sources (e.g., cooking activities or biomass burning, etc.), produced by indoor reactions (e.g., ozone-initiated reactions occurring during cleaning activities) or penetrating from outdoor spaces. They are capable to cross the respiratory system, carrying toxic compounds, depositing in the deepest airways, and provoking negative health effects. Recently, smaller particles were recognized as most critical for human health and the related metrics (number and surface area) being more representative of the health effects with respect to particle mass (e.g., PM10). For this reason, an in-depth measurement and monitoring of particle concentrations, particle size distributions and relative composition is having more and more attention. Indoor air quality also involves the presence of biological contaminants, fungi (including yeasts), pathogens, allergens (from fungi, pets, insects, and other sources, including pollen) and toxins. Indoor air biological contamination may have different sources, namely outdoor air, the human body, bacteria growing indoors, and pets. Concerning indoor environments, the most important biologic contaminants are microorganisms, allergens, and toxins. Recently, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has brought renewed attention to virus-laden respiratory particles in disease transmission (airborne transmission). The measurement of expelled respiratory particles represents the preliminary step to apply the existing risk models of infection in indoor environments and/or in close-proximity configurations. Indeed, such models are strongly dependent on the viral emission of the infected subject which is, in turn, influenced by the viral load carried by the respiratory particles (that can be obtained from PCR tests) and by the number of emitted particles. In this thesis work, some currently missing aspects regarding airborne and respiratory particles were explored and discovered, with the aim to fill some knowledge gap in terms of characterization of emission, its associated risk, and possible eco-feedback approach with the goal of spreading awareness related to indoor air quality-issues. In Chapter 1, a general overview of aerosol dynamics, classification, measurement, health effects and regulatory framework is provided. In Chapter 2, a description of airborne and respiratory particles, the related risks, and methods to improve people’s awareness is detailed. Considering that airborne particles represent one of the most significant environmental risks people have to face, different airborne particle indoor sources (e.g., candles, incenses, mosquito coils) where physically and chemically analyzed according to their size through a detailed experimental analysis presented in Chapter 3. Indeed, the existing risk models on human health (e.g., related to the occurrence of lung cancer) revealed a strong correlation with the sub-micron airborne particles (with respect to super-micron ones) related to the exposure of different sources, especially cooking activities that represent the main contributor to the emission of sub-micron airborne particles in free-smoking homes. To this end, a simplified approach to evaluate the lung cancer risk related to airborne particles emitted by indoor sources was developed and presented in Chapter 4. If it is true that knowledge is fundamental, its transfer is even more important, especially for those who are not directly part of the scientific community. Indeed, an Eco-Feedback strategy, usually adopted in energy savings, was designed for indoor air quality issues, with the objective to increase awareness and stimulate behavioral changes among occupants. The success of the strategy emerged both in terms of promoting behavioral changes of the occupants and reducing the concentration levels while airborne particle emitting sources (i.e., cooking) were in operation as shown in Chapter 5. Finally, as concern the respiratory particles, since the quantification of emitted respiratory particles is critical in calculating the risk of infection in confined environments and few studies are currently available in the literature on children, an experimental analysis aimed at measuring the respiratory particles emitted by children during speaking activities was carried out and here presented (Chapter 6).