Novel Methods for Assessing Exposures and Health Effects of Ultrafine Particles and Nitrogen Oxides
exposure to traffic-related air pollution (TRAP) is associated with cardiovascular
morbidity and mortality. The impact of the smallest size fraction of particulate matter,
ultrafine particulate matter (UFP, measured as particle number concentration or PNC) is
less well-established. Only one study examined the joint effects of PNC and gaseous
components of TRAP. We consider... read moreed these effects within the prospective Boston Puerto
Rican Health Study (BPRHS; n=902 participants in Chelsea and Boston, Massachusetts). We
assessed spatial and temporal factors affecting the distribution and covariation of PNC
and nitrogen oxides (NOx). We found higher correlations in times and locations where
traffic-related sources have greater impact. We developed a land use regression model to
predict NOx concentrations at <200-m and 1-h resolution in Chelsea and Boston for
2003-2015 using data from a mobile platform and a fixed site. The model was stable with
two cross-validation methods and predicted concentrations at three validation sites
(adjusted-R2=0.53-0.62). Using the NOx model and a previously developed PNC model, we
estimated participants' annual average exposures to both pollutants. We tested the
independent and joint effects of long-term exposure to PNC and NOx on blood pressure and
a biomarker of systemic inflammation (C-reactive protein). We found limited evidence
that the pollutants affect diastolic blood pressure but the associations with each of
the outcomes were inconsistent. Effect modification was observed by sex, smoking, and
baseline hypertension status. To understand how PNC affects cardiovascular outcomes, we
investigated the use of an instrument for a mediator to test mechanistic hypotheses
within observational studies. We tested the impact of violations of the strong
assumptions of this method in a simulation study. The method was more robust against
confounding of the instrument-outcome relationship than the presence of
instrument-outcome paths independent of the mediator. To improve exposure assessment of
PNC, we measured the population-specific age-, sex-, weight-, and physical
activity-adjusted minute respiratory volumes for a population like the BPRHS population.
These values were applied to our previously developed exposure metric, the particle
inhalation rate (PIR). The population-specific values did not change the PIR or health
effect estimates. Our PIR algorithm is generalizable to diverse
Thesis (Ph.D.)--Tufts University, 2018.
Submitted to the Dept. of Civil Engineering.
Advisor: David Gute.
Committee: Doug Brugge, John Durant, Jon Levy, and Mark Woodin.
Keywords: Environmental health, Epidemiology, and Environmental science.read less