Opportunities and limitations of aerosol sensors to urban air quality monitoring

Joel Kuula

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Atmospheric particles are one of the leading mortality risk factors in the global burden of disease analysis. The association between particulate mass of particles smaller than 2.5 μm in diameter (PM2.5) and cardiovascular and pulmonary diseases has been characterized by multiple epidemiological studies, and varying estimates suggest that several million premature death occur globally each year due to PM2.5 exposure. Mitigation of the adverse health effects of particulate matter requires comprehensive understanding of their sources and dynamic processes, such as spatial dispersion. Recent emergence and development of aerosol sensors, which are typically characterized as small, relatively low cost and easy to use, have enabled new opportunities in air quality monitoring. As a result of their practical convenience, sensors can be deployed to the field in high quantities which, consequently, enables network-type, spatially comprehensive measurements. However, with more simplified and less expensive measurement approach, less accurate and reliable results may be expected. This study aimed to evaluate and characterize the accuracy and usability of aerosol sensor to urban air quality measurements. The investigation focused on two of the most prominent measurement techniques applicable to sensor type monitoring; optical and diffusion charging-based techniques. Sensors utilizing optical technique were evaluated in laboratory and field studies for their error sources and particle size-selectivity, specifically. Diffusion charging-based sensors, which measure lung deposited surface area of particles, were evaluated in the field for their suitability to measure combustion emitted particles, such as vehicular exhaust and residential wood combustion emissions. Results of the study indicated that optical aerosol sensors are unlikely to be fit for long-term regulatory monitoring. The main issues preventing this arise from their improper calibration which poses a significant risk of data misinterpretation; none of the laboratory evaluated sensors measured particle sizes which their technical specifications implied. On the other hand, field tests showed that when the measured size fraction was targeted to match the true detection range of the sensor, highly accurate and repeatable results were obtained. This implies that, while the usability of optical sensors is limited in their current form, the concept and vision of a sensor driven air quality monitoring network remains valid and achievable. In comparison to optical sensors, diffusion charging-based sensors were found to be more mature in terms of their technological development. The evaluated sensors exhibited accurate and stable performance throughout the test campaigns and were shown to be particularly well-suited the measurement of combustion emitted particles. As optical methods cannot be used to measure ultrafine particles reliably, and particles emitted from combustion sources have a significant contribution to air quality, diffusion charger sensors would be a valuable addition to be used alongside the typically used measurement techniques, such as the optical based.
Translated title of the contributionAerosolisensoreiden mahdollisuudet ja rajoitteet kaupunki-ilmanlaadun seurannassa
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Tammi, Kari, Supervisor
  • Timonen, Hilkka, Advisor
  • Aurela, Minna, Advisor
Publisher
Print ISBNs978-952-60-3842-1
Electronic ISBNs978-952-60-3843-8
Publication statusPublished - 2020
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • urban air quality
  • particulate matter
  • aerosol sensor

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