<p>Aerosols are solid or liquid particles
that span in size from a few nanometers to tens of micrometers. They are important
in both outdoor and indoor environments due to their impact on climate and
human health.
Many aerosol processes of interest to the environment, health, and
filtration are strongly size-dependent.
Aerosol particle size distributions (PSDs) provide a basis to better
understand outdoor and indoor air pollution sources, evaluate human exposure to
air pollution, and aerosol deposition in the human respiratory tract and
filters in building ventilation systems. Monitoring the temporal evolution of aerosol
PSDs enable for characterization of dynamic aerosol transport and
transformation processes, such as direct emissions, nucleation, condensation,
coagulation, resuspension, deposition, and filtration. This thesis presents three studies on the PSDs
of: (i.) urban aerosols in cities around the world in order to identify
geographical trends in the shape and magnitude of PSDs and to frame future research
needs for PSD observations at a global-scale, (ii.) synthesized salt particles
from a novel thermal aerosol generator to evaluate its suitability for air filter
testing, and (iii.) indoor biological particulate matter (<i>bio</i>PM) to characterize transient inhalation exposures of infants
and adults to resuspended <i>bio</i>PM from
carpet dust induced by crawling and walking.</p>
<p>First,
this thesis presents the current state-of-knowledge of urban aerosol PSDs by critically
analyzing <i>n</i>=793 urban aerosol PSD
observations made between 1998 to 2017 in <i>n</i>=125 cities in <i>n</i>=51
countries across the following regions of the
world: Africa (AF), Central, South, and Southeast Asia
(CSSA), East Asia (EA), Europe (EU), Latin America (LA), North America,
Australia, and New Zealand (NAAN), and West Asia (WA). Prominent geographical variations in the
shape and magnitude of urban aerosol number and mass PSDs were identified and significant
variations in number PSDs were found between cities in EU and NAAN with those
in CSSA and EA. Most PSD observations published
in the literature are short-term, with only 14% providing data for longer than
six months. There is a paucity of PSDs
measured in AF, CSSA, LA, and WA, demonstrating the need for long-term aerosol
measurements across wide size ranges in many cities around the globe. Inter-region variations in PSDs have
important implications for population exposure, driving large differences in
the urban aerosol inhaled
deposited dose rate received in each region of the human
respiratory system. Similarly, inter-region
variations in the shape of PSDs impact the penetration of urban aerosols
through filters in building ventilation systems, which serve as an important
interface between the outdoor and indoor atmospheres. The results of this critical review
demonstrate that global initiatives are urgently needed to develop
infrastructure for routine and long-term monitoring of urban aerosol PSDs
spanning the nucleation to coarse modes.</p>
<p>Second, this
thesis evaluates a newly designed commercially available thermal aerosol
generator for ageing air filters in building heating, ventilation, and
air-conditioning (HVAC) systems. The
physical characteristics of the synthesized salt aerosol (NaCl and KCl) under
different generator operational conditions were evaluated. The shape of the number and mass PSD output of the thermal
aerosol generator are similar to those found in outdoor (urban) and indoor air
and can be modulated by varying the rate at which the salt stick is fed into
the flame. The morphology of the NaCl
and KCl particles varied with size, with compact
spherical or cubic structures observed below 100 nm and agglomerates
observed above 100 nm. The thermal
aerosol generator is a cost-effective technique for rapid ageing of HVAC
filters with a PSD that more accurately represents, compared to conventional
loading dusts, what filters encounter in real HVAC installations.</p>
<p>Lastly, this thesis characterizes infant and adult
inhalation exposures and respiratory tract deposited dose rates of resuspended <i>bio</i>PM from carpets. Chamber experiments were conducted with a
robotic crawling infant and an adult performing a walking sequence. Breathing zone (BZ) size distributions of
resuspended fluorescent biological aerosol particles (FBAPs), a <i>bio</i>PM proxy, were monitored in
real-time. FBAP exposures were highly
transient during periods of locomotion.
Both crawling and walking delivered a significant number of resuspended
FBAPs to the BZ, with concentrations ranging from 0.5-2 cm<sup>-3</sup>. Infants and adults are primarily exposed to a
unimodal FBAP size distribution between 2 and 6 μm, with infants receiving greater exposures to
super-10 μm FBAPs. In just one minute
of crawling or walking, 10<sup>2</sup>-10<sup>3</sup> resuspended FBAPs can
deposit in the respiratory tract, with an infant receiving much of their
respiratory tract deposited dose in their lower airways. Per kg body mass, an infant will receive
nearly four times greater respiratory tract deposited dose of resuspended FBAPs
compared to an adult.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12252050 |
| Date | 07 May 2020 |
| Creators | Tianren Wu (8802641) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/STUDIES_ON_AEROSOL_SIZE_DISTRIBUTIONS_EMISSIONS_AND_EXPOSURES/12252050 |
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