Studies on Aerosol Size Distributions, Emissions, and Exposures

Tianren Wu, Purdue University

Abstract

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 (bioPM) to characterize transient inhalation exposures of infants and adults to resuspended bioPM from carpet dust induced by crawling and walking. First, this thesis presents the current state-of-knowledge of urban aerosol PSDs by critically analyzing n=793 urban aerosol PSD observations made between 1998 to 2017 in n=125 cities in n=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. 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.

Degree

Ph.D.

Advisors

Boor, Purdue University.

Subject Area

Atmospheric Chemistry|Atmospheric sciences|Atomic physics|Chemistry|Morphology|Nuclear physics|Physics

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