UC Berkeley

Volatile organic compounds (VOCs) are emitted to the atmosphere and play important rolesin tropospheric chemistry. Atmospheric VOC oxidation by hydroxyl radicals, ozone, and nitrate leads to formation of a broad array of secondary chemicals, including ozone and secondary organic aerosol, both of which have impacts on climate change and public health. Indoors, VOCs themselves have a myriad of effects on public health, ranging from eye irritation to carcinogenesis, making them important molecules of study from both air pollution and health perspectives. VOCs also undergo oxidation indoors, the products of which can be important for human exposure, indoor chemistry, or transport to the outdoors via ventilation. Indoor air chemistry and VOC sources have been studied to a lesser extent than their outdoor atmospheric counterparts. This work takes important steps towards understanding VOC composition and sources in different residential microenvironments, indoor dynamics, and removal in order to expand knowledge on the role indoor emissions play in atmospheric processes. In order to expand on current knowledge of the effects of occupant behaviors on indoor residential environments, Chapter 2 synthesizes PTR-TOF-MS measurements across four indoor air campaigns to investigate the emissions and behavior of a class of entirely synthetic and understudied VOCs found in personal care products: volatile methyl siloxanes (VMS). While their health effects are inconclusive, their unique chemical structure results in volatility properties that are worth exploring further. Cyclic VMS (D3-D6) were found to be the most abundant siloxane species across all four campaigns and were attributed to personal care product usage. D3 and D4 siloxane emissions also were emitted from oven use. Their primary removal mechanism was ventilation. Linear VMS (L4, L5) and three additional organosilicon compounds (silyl acetate, caprylyl methicone, and C7H21O3Si3 +) were detected in a subset of indoor environments and were also attributable to personal care products. The primary removal mechanism for the linear VMS appeared to be sorption to indoor surfaces, while the remaining organosilicon compounds were removed via ventilation. This chapter contributes new knowledge regarding the drivers of VMS emissions, their range of sources, and their sorptive behavior on indoor surfaces. The VMS species discussed in Chapter 2 were detected at varying concentrations throughout the living zone (defined as the region of the house where occupants spend their time), prompting the question of how VOC composition can vary in different rooms, or 2 microenvironments, within a home. Chapter 3 starts to address this question by characterizing the VOC composition of air in a closed bedroom overnight, a microenvironment where humans spend about one third of their day. Nearly 100 VOCs were found to have significant enhancement in the bedroom overnight compared to both the kitchen of the same house and the outdoors, confirming their origin in the bedroom. These species could be attributed to several source categories, including building emissions, occupant bioeffluents, and transport. Nightly air change rates in the bedroom were estimated using CO2 measurements under two limiting conditions: (1) air exchange in the bedroom occurs only with the outdoors and (2) only with the kitchen, the room most closely coupled with the bedroom. These estimates were subsequently used to determine VOC emission rates, which varied significantly and highlight the need for more measurements across a range of residences. This chapter contributes new knowledge regarding VOC composition and emission factors in a typical occupied bedroom. Another understudied but ubiquitous indoor microenvironment is the residential attic; little is known about VOC emissions directly into the attic space or about their transport to the outdoors and potential impact on atmospheric chemistry. Chapter 4 addresses this knowledge gap by characterizing VOC composition of a typical residential attic, quantifying interzonal flow rates using inert tracer concentrations and emission rates, and estimating direct attic VOC emission rates. About 40 VOCs, including furanoids, acids, and sulfur- or nitrogen-containing compounds, were found to be enhanced in the attic and strongly correlated with furfural, which was used as a benchmark for wood decomposition products. Flow rate analysis was used to determine that air exchange between the attic and the outdoors increased by a factor of three between the morning and the afternoon as a result of changes in temperature. Additionally, the emission rates of VOCs attributable to wood decomposition and building materials were found to have an exponential relationship to temperature, consistent with biogenic VOC emissions. The calculated emission rates were used to estimate daily mass emissions to the outdoors, which has significant implications for emissions inventories that currently do not take furanoid compounds or their atmospheric chemistry into account. This chapter contributes new knowledge regarding direct attic emissions, interzonal transport, and the impact of attic emissions on ambient air. Finally, Chapter 5 contextualizes the work presented in Chapters 2-4 and offers insights into how future work can build on the knowledge created here to the benefit of the public. Key recommendations include enhancing the current suite of VOC measurements by expanding data collection to include a myriad of household types, occupant densities, and ambient conditions. This, in turn, will improve average emission factor estimates for emissions inventories and air quality models.