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Differentiated health impacts of primary and secondary ultrafine particles

Periodic Reporting for period 1 - Health1UP2 (Differentiated health impacts of primary and secondary ultrafine particles)

Período documentado: 2017-09-07 hasta 2019-09-06

During the past few decades, population studies have consistently linked the exposure to particulate matter (PM) in ambient air to various negative health effects. Traditionally, these studies have focused in exposures to mass concentrations of PM with a diameter ≤10 and ≤2.5 µm (PM10 and PM2.5 respectively) because they are extensively measured across Europe. However, negative health effects are expected to be enhanced with decreasing particle size, since the upper airways are inefficient at filtering ultrafine particles (UFP, PM ≤ 0.1 µm). Recent research indicates sufficient reason to believe that UFP are responsible for negative health effects otherwise attributed to larger size fractions of PM. The answer to this question is important as it would lead to authorities having to control different sources of particles. Unlike PM10 or PM2.5 UFP contribute very little to PM mass, but they are dominant at particle number concentrations (PNC). UFP might have different origins, which is also associated with their size.Source apportionment techniques, such as Positive Matrix Factorization (PMF) have been extensively applied to identify and quantify the sources contributing to PM mass concentrations. No previous study has tried to tackle the fundamental issue of identifying associations between the different sources of UFP, rather than using surrogates for primary combustion emissions such as black carbon (BC) or proximity to mayor highways. Moreover, although a growing literature is pointing towards UFP as the main culprit of human health impairment, there are currently no legal ambient standards for UFP. Future revisions of the Air Policy by the European Commission should include discussions about the inclusion of new standards for other metrics and pollutants, such as UFP and Black Carbon (a good traffic tracer). Therefore, further information on the health effects of UFP is highly needed.
Hence, this study aims to identify the different sources contributing to ultrafine PNC and to disentangle the health effect associated with each of these sources to get a full picture of the dimension of the threat that UFP is posing to Public Health. The main objectives of the Health1UP2 (Differentiated health impacts of primary and secondary ultrafine particles) are:
- To identify and quantify the sources of UFP in the cities of London (UK), Barcelona (Spain), Zurich (Switzerland) and Helsinki (Finland) based on long time-series of size-segregated UFP (particle number size distributions) and other pollutants.
- To determine the health impacts (with mortality and hospital admissions as outcomes) of the exposure to the different sources of UFP in London, Barcelona, Zurich and Helsinki.
The results of this work will (i) serve as indication to the corresponding authorities of which air pollutants should be included in future EU legislation about air quality (ii) add insight to the growing body of literature on the health effects of UFP (iii) tackle an important issue not being considered yet: the health effects of UFP according to their origin.
We performed Positive Matrix Factorisation, a source apportionment technique, on Particle Number Size Distribution (PNSD) to identify and quantify the sources contributing to ultrafine PNC. We performed the analyses separately for each city and different periods were covered according to the PNSD data availability. Once the different sources of UFP were identified and quantified, we performed an epidemiological time series study to evaluate the associations of the exposure to the different sources and cause-specific daily mortality in each of the cities. We evaluated the short-term effects of different sources of UFP and total particle number concentrations in mortality with a time-series design using generalized linear models with quassi-Poisson regression. We investigated separately the effect of the same day exposure (lag 0) up to 5 days before (lag 5).

SOURCES OF PARTICLE NUMBER SIZE DISTRIBUTIONS
Our analyses yielded to very interesting results. Traffic sources were by far the main contributor to UFP in all cities. Photonucleation particles were much more important during the summer in Barcelona due to the higher solar radiation in comparison to wintertime. We identified airport emissions as a source affecting all the stations, although we were unable to quantify its contribution as airport emissions were mixed with the photonucleation and traffic nucleation particles.

HEALTH EFFECTS OF THE SOURCES OF ULTRAFINE PARTICLES
This work is in process.. This work will add to a different number of studies that show inconsistent results between UFP and mortality. These results may be due to the high spatial variability of ultrafine particle number concentrations, which makes the exposure assessment extremely complicated.
We evaluated the effects on daily mortality of different sources of UFP. This is a novel approach, as very few studies have attempted to unravel the health effects of specific sources of ultrafine particles. We are still obtaining results and, in the near future, we will evaluate the associations between the sources of UFP and hospital admissions.

The impact of this study at a socio-economic and societal level is important. We have identified traffic as the main contributor to the levels of UFP. We have also quantified the contribution of traffic to total particle number and, thus, we know that putting in place policies to reduce traffic emissions could drastically diminish ultrafine particle number concentrations.

Although this study was not able to link the exposure to ultrafine particles and its sources to consistent increases of daily mortality, other studies are pointing towards ultrafine particles as the most hazardous. Thus, targeted policies for decreasing emissions that contribute to ultrafine particles will result in huge improvement of public health.
Relative contribution of the sources at the different cities (annual averages)