The Near-Road Exposures and Effects of Urban Air Pollutants Study (NEXUS): study design and methods

Abstract

The Near-Road Exposures and Effects of Urban Air Pollutants Study (NEXUS) was designed to examine the relationship between near-roadway exposures to air pollutants and respiratory outcomes in a cohort of asthmatic children who live close to major roadways in Detroit, Michigan USA. From September 2010 to December 2012 a total of 139 children with asthma, ages 6-14, were enrolled in the study on the basis of the proximity of their home to major roadways that carried different amounts of diesel traffic. The goal of the study was to investigate the effects of traffic-associated exposures on adverse respiratory outcomes, biomolecular markers of inflammatory and oxidative stress, and how these exposures affect the frequency and severity of respiratory viral infections in a cohort of children with asthma. An integrated measurement and modeling approach was used to quantitatively estimate the contribution of traffic sources to near-roadway air pollution and evaluate predictive models for assessing the impact of near-roadway pollution on children's exposures. Two intensive field campaigns were conducted in Fall 2010 and Spring 2011 to measure a suite of air pollutants including PM2.5 mass and composition, oxides of nitrogen (NO and NO2), carbon monoxide, and black carbon indoors and outdoors of 25 participants' homes, at two area schools, and along a spatial transect adjacent to I-96, a major highway in Detroit. These data were used to evaluate and refine models to estimate air quality and exposures for each child on a daily basis for the health analyses. The study design and methods are described, and selected measurement results from the Fall 2010 field intensive are presented to illustrate the design and successful implementation of the study. These data provide evidence of roadway impacts and exposure variability between study participants that will be further explored for associations with the health measures.

Fig. 1

Location of roadway segments around which children were recruited to participate in NEXUS and the locations of homes, schools and the I-96 site where traffic-related air pollutants were measured (see Section 2.3). Data from homes N-1, S-1 and S-2 are discussed in Sections 3.2 and 3.3.

Fig. 2

Linked air quality and exposure models and their data inputs to estimate exposure metrics for epidemiological analysis.

Fig. 3

Daily integrated (24 h) PM_2.5 concentrations (μg/m³) during the Fall 2010: (a) PM_2.5 mass with week 6 data highlighted in dashed box, (b) PM_2.5 mass for week 6 with data from two HD homes (S-1 and S-2) and one LT home (N-1), (c) PM_2.5 black carbon (BC) with week 6 data highlighted in dashed box, and (d) PM_2.5 BC for week 6 with data from homes S-1, S-2 and N-1.

Fig. 4

Example of sector apportionment and wind rose analysis of continuous black carbon concentrations measured simultaneously outdoors at two homes on different sides of I-94 for approx. 5 days during the Fall 2010. Detailed roadways have been removed to maintain participant confidentiality.

Fig. 5

Early morning black carbon (BC) concentrations measured continuously indoors and outdoors of two homes.