Spatial and Temporal Profiles of Personal PM Exposure in Urban Childhood Asthma

ISEE-1542

Background:

Childhood asthma is a complex disease with both environmental and genetic risk factors. Elucidation of the environmental risk factors is confounded by difficulties associated with monitoring and distinguishing children's exposure patterns across varying micro-environments. The goal of this research was to track children's movement and associated particulate matter exposure through distinct micro-environments across the course of a day and to then visualize and analyze their exposure patterns within each micro-environment. We report findings on exposure to fine particulate matter here, however, our method is adaptable to any stressor or contaminant that can be monitored by a portable sensor in real-time.

Methods:

This method integrates real-time monitors, global positioning system (GPS) receivers, and a geographical information system (GIS). The sampling apparatus consists of a backpack containing a portable GPS receiver, an ambient temperature sensor, a aerosol monitor (pDR-1200 with cyclone) with attached filter, and a pump. Thirty-two elementary school-age children wore the backpack for four consecutive days (Mon-Thur) during two distinct weeks throughout the school year resulting in over 200 daily samples. The time-referenced signals for fine particulate matter concentration, ambient temperature, and location were synchronized and merged within a GIS to analyze and visualize the children's exposures. We developed and applied algorithms to apportion exposure data into four micro-environments: school, home, morning transit and afternoon transit.

Results:

Incremental improvements to the method after a pilot study included higher-sensitivity GPS receivers and an ambient temperature monitor. The new GPS receivers decreased lost and aberrant signals to less than 5%. Analysis of variance indicated that PM concentrations measured within the four micro-environment categories were significantly different from each other (P < 0.001). Rank estimates for average exposure, from lowest to highest, were: school, morning transit, afternoon transit and home. Personal breathing-zone concentrations within the home were more than three times greater than at school. Interestingly, PM concentrations measured during afternoon transit were nearly twice that of morning transit, on average. Ambient temperature data provided insight into indoor vs. outdoor exposures and also allowed for the association of PM concentration flux with forced-air heating cycles indoors. Use of a GIS allowed data to be projected onto a map of the study area for visual interpretation of exposure across distinct micro-environments.

Conclusions:

A high resolution, space and time-referenced sampling method for PM exposure assessment for asthmatic children was developed. With a 10-second temporal resolution and a <3 m spatial resolution outdoors (∼10 m indoors), the method allows examination of exposure patterns that were previously impossible with traditional exposure assessment techniques (i.e., time-integrated filter measurements). This method collects and automatically apportions over 8600 personal exposure data points per day with both high resolution and accuracy. The method has lead to more reliable representation of exposures in these micro-environments and allows preparation of a more detailed 'exposure budget' for each child. Further research using this methodology will support analysis of health outcomes associated with micro-environmental exposures and towards assessment of interventional techniques to reduce exposure.