Personal exposure monitoring wearing protocol compliance: an initial assessment of quantitative measurement.

Personal exposure sampling provides the most accurate and representative assessment of exposure to a pollutant, but only if measures are implemented to minimize exposure misclassification and reduce confounders that may cause misinterpretation of the collected data. Poor compliance with personal sampler wearing protocols can create positive or negative biases in the reported exposure concentrations, depending on proximity of the participant or the personal sampler to the pollutant source when the monitor was not worn as instructed. This paper presents an initial quantitative examination of personal exposure monitor wearing protocol compliance during a longitudinal particulate matter personal exposure monitoring study of senior citizens of compromise health in North Carolina. Wearing compliance varied between participants because of gender or employment status, but not longitudinally or between cohorts. A minimum waking wearing compliance threshold, 0.4 for this study of senior citizens, is suggested to define when personal exposure measurements are representative of a participant's exposure. The ability to define a minimum threshold indicates data weighting techniques may be used to estimate a participant's exposure assuming perfect protocol compliance.

The design and field implementation of the Detroit Exposure and Aerosol Research Study.

The US Environmental Protection Agency recently conducted the Detroit Exposure and Aerosol Research Study (DEARS). The study began in 2004 and involved community, residential, and personal-based measurements of air pollutants targeting 120 participants and their residences. The primary goal of the study was to evaluate and describe the relationship between air toxics, particulate matter (PM), PM constituents, and PM from specific sources measured at a central site monitor with those from the residential and personal locations. The impact of regional, local (point and mobile), and personal sources on pollutant concentrations and the role of physical and human factors that might influence these concentrations were investigated. A combination of active and passive sampling methodologies were employed in the collection of PM mass, criteria gases, semivolatile organics, and volatile organic compound air pollutants among others. Monitoring was conducted in six selected neighborhoods along with one community site using a repeated measure design. Households from each of the selected communities were monitored for 5 consecutive days in the winter and again in the summer. Household, participant and a variety of other surveys were utilized to better understand human and household factors that might affect the impact of ambient-based pollution sources upon personal and residential locations. A randomized recruitment strategy was successful in enrolling nearly 140 participants over the course of the study. Over 36,000 daily-based environmental data points or records were ultimately collected. This paper fully describes the design of the DEARS and the approach used to implement this field monitoring study and reports select preliminary findings.

Maximizing Data Quality in the Gravimetric Analysis of Personal Exposure Sample Filters.

The weighing of particle sampler filters has always been plagued by problems in the weighing environment: humidity, temperature, drafts, vibration, and electrostatic charges on the filters. These are particularly critical for samples with small mass collections, such as those encountered in personal exposure monitoring for PM25. While modern electronic balances offer substantial reductions in the effects of temperature and vibration, these balances are still sensitive to factors such as thermal drafts and zero shifts from tilting. Drafts may be controlled through room ventilation modifications, and zero drift can be eliminated by computer-assisted data collection algorithms. A less well-understood influence is static charge, which is often controlled with a simple radioactive neutralizer. Although radioactive neutralizes are effective, their effectiveness decays rapidly with time, and their use may be objectionable for nontechnical reasons. We have analyzed a number of environmental factors influencing gravimetric microbalance operations and have developed methods to minimize or eliminate them.