Abstract
BackgroundThe evidence on the association between ultrafine (UFP) particles and mortality is still inconsistent. Moreover, health effects of specific UFP sources have not been explored. We assessed the impact of UFP sources on daily mortality in Barcelona, Helsinki, London, and Zurich. MethodsUFP sources were previously identified and quantified for the four cities: daily contributions of photonucleation, two traffic sources (fresh traffic and urban, with size mode around 30 nm and 70 nm, respectively), and secondary aerosols were obtained from data from an urban background station. Different periods were investigated in each city: Barcelona 2013–2016, Helsinki 2009–2016, London 2010–2016, and Zurich 2011–2014. The associations between total particle number concentrations (PNC) and UFP sources and daily (natural, cardiovascular [CVD], and respiratory) mortality were investigated using city-specific generalized linear models (GLM) with quasi-Poisson regression. ResultsWe found inconsistent results across cities, sources, and lags for associations with natural, CVD, and respiratory mortality. Increased risk was observed for total PNC and natural mortality in Helsinki (lag 2; 1.3% [0.07%, 2.5%]), CVD mortality in Barcelona (lag 1; 3.7% [0.17%, 7.4%]) and Zurich (lag 0; 3.8% [0.31%, 7.4%]), and respiratory mortality in London (lag 3; 2.6% [0.84%, 4.45%]) and Zurich (lag 1; 9.4% [1.0%, 17.9%]). A similar pattern of associations between health outcomes and total PNC was followed by the fresh traffic source, for which we also found the same associations and lags as for total PNC. The urban source (mostly aged traffic) was associated with respiratory mortality in Zurich (lag 1; 12.5% [1.7%, 24.2%]) and London (lag 3; 2.4% [0.90%, 4.0%]) while the secondary source was associated with respiratory mortality in Zurich (lag 1: 12.0% [0.63%, 24.5%]) and Helsinki (4.7% [0.11%, 9.5%]). Reduced risk for the photonucleation source was observed for respiratory mortality in Barcelona (lag 2, −8.6% [−14.5%, −2.4%]) and for CVD mortality in Helsinki, as this source is present only in clean atmospheres (lag 1, −1.48 [−2.75, −0.21]). ConclusionsWe found inconsistent results across cities, sources and lags for associations with natural, CVD, and respiratory mortality.
Highlights
The evidence on the association between ultrafine (UFP) particles and mortality is still inconsistent
Much less information is available on the effects on mortality of ul trafine particles (UFP; usually defined as particles
Total PNC was strongly correlated with the fresh traffic (r > 0.81) and with the urban source (r > 0.61) in all cities as these two sources are the main contributors to PNC
Summary
The evidence on the association between ultrafine (UFP) particles and mortality is still inconsistent. Some positive associations between short-term exposure to UFP and mortality have been reported (Breitner et al, 2011; Stolzel et al, 2007), many of the studies reported weak or no evidence (Atkinson et al, 2010; Branis et al, 2010; Lanzinger et al, 2016; Stafoggia et al, 2017) These inconsistencies may be due to (1) the difficulty in accurately estimating the exposure due to the large change over short distances of UFP number concentrations (Zhu et al, 2002) and to (2) a different relative and absolute contribution of the sources of UFP on the different days (Tobías et al, 2018).
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