Combustion Processes Laboratories

Rural kitchens of solid-fuel burning households constitute the microenvironment responsible for the majority of human exposures to health-damaging air pollutants, particularly respirable particles and carbon monoxide. Portable nephelometers facilitate cheaper, more precise, time-resolved characterization of particles in rural homes than are attainable by gravitational methods alone. However, field performance of nephelometers must contend with aerosols that are highly variable in terms of chemical content, size, and relative humidity. Our investigation of relationships between 24-hour optical and gravitational particle measurements in rural Chinese kitchens depicts that where relative humidity remained below 95%, nephelometric response was strongly linear despite complex mixtures of aerosols. Where 95% relative humidity was exceeded for even a brief duration, nephelometric data were nonsystematically distorted, and neither concurrent relative humidity measurements nor use of robust statistical measures of central tendency offered means of correction. This nonsystematic distortion is particularly problematic for rural exposure assessment studies, which emphasize upper quantiles of timeresolved particle measurements both within and between samples. Precise, accurate interpretation of optically resolved short-term particle concentrations requires short-term gravitational sampling concurrent with optical methods.