Ambient fine particles are known to cause millions of premature deaths worldwide annually. Even though the negative health effects of fine particles are indisputable, the mechanisms behind these effects are not completely understood. For example, estimations of the premature deaths caused by fine particles vary considerably in different studies. Also, the negative health effects seem to be dependent for example on the geographical region.
According to Teemu Lepistö, one explanation for the uncertainty is related to the common air quality monitoring metrics. Ambient fine particles are commonly measured based on their mass concentration (PM2.5).
“Fine particles cover all particles from nanometres up to 2.5 micrometres. Mass concentration emphasises the larger particles, and, therefore, particle composition as well as the concentrations of ultrafine particles (smaller than 0.1 micrometres) or black carbon cannot be well estimated based on the particle mass measurement. Various studies indicate that all these parameters are important in terms of the negative health effects of particles,” says Lepistö.
Also, particle lung deposition has gained attention as a potential explanation for the varying health effects of particles. Particle lung deposition is strongly dependent on the particle size, which is related to particle sources, composition, and atmospheric aging. In his thesis, Lepistö investigated spatial differences of the concentrations and characteristics of lung depositing particles.
“Different lung deposition of particles in different environments could explain spatial differences of particle health effects. Especially particle surface area has been suggested to be an important parameter in terms of the health effects in toxicological studies,” he says.
In Finland, main emission sources are transport, industry and wood burning
In his research, Lepistö developed a new method to measure particle lung deposited surface area. The new method was then utilised in various urban environments, covering road traffic sites, airports, detached housing residential areas, shipping and industrial sites in Finland, Germany, Czechia, Chile, and India.
He observed that especially emissions of ultrafine particles and black carbon are important in terms of the lung deposited surface area. Both can cause significant exposure in the human lungs even if the simultaneously measured PM2.5 concentration is low.
“Lung deposition of ultrafine particles and black carbon are especially relevant in countries where air quality can be usually considered to be good, like Finland. For example, road traffic, aircrafts, and industrial sites can strongly affect the nearby ultrafine particle concentrations despite a minimal effect on PM2.5. Thus, low PM2.5 does not mean that nearby emission sources would not cause considerable adverse health effects.”
The situation was, however, very different in Chile and India compared to Europe. In Chile and India, general air quality is typically worse than in Europe, which also means higher PM2.5 concentrations.
“The nearby emission sources were also important in terms of particle lung deposition in Chile and India. However, their relative role in the lung deposited surface area was much less significant than in Europe due to the lung deposition of regional aerosol,” Lepistö states.
Overall, Lepistö demonstrated that the concentrations and characteristics of lung depositing particles are strongly dependent on the nearby emission sources and geographical region. Thus, the results offer a partial explanation for the varying health effects of fine particles as these differences cannot be well observed with traditional air quality monitoring metrics, like the PM2.5. Also, the results highlight the need for location and country specific emission mitigation strategies.
Public defence on Friday 24 May
The doctoral dissertation of MSc (Tech) Teemu Lepistö in the field of aerosol physic titled Lung deposited surface area of ambient fine particles: measurement methodologies and location-dependent characteristics will be publicly examined at the Faculty of Engineering and Natural Sciences at Tampere University at 12 o’clock on Friday the 24th of May 2024, at Hervanta campus, Sähkötalo auditorium SA203 (Korkeakoulunkatu 3, Tampere).
The opponent will be Professor Heikki Junninen, University of Tartu. The Custos will be Professor Topi Rönkkö from Tampere University.
The doctoral dissertation is available online.
The public defence (in Finnish) can be followed via remote connection.