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.