Fischer Susan L, Koshland Catherine P
Environmental Health Sciences, School of Public Health, University of California, Berkeley, CA 94720, USA.
J Expo Sci Environ Epidemiol. 2007 Mar;17(2):141-50. doi: 10.1038/sj.jes.7500486. Epub 2006 May 3.
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. Previous field validations of nephelometer performance in residential settings explore relatively low particle concentrations, with the vast majority of 24-h average gravitational PM2.5 concentrations falling below 40 microg/m3. We investigate relationships between 24-h gravitational particle measurements and nephelometric data logged by the personal DataRAM (pDR) in highly polluted rural Chinese kitchens, where gravitationally determined 24-h average respirable particle concentrations were as high as 700 microg/m3. We find that where relative humidity remained below 95%, nephelometric response was strongly linear despite complex mixtures of aerosols and variable ambient conditions. Where 95% relative humidity was exceeded for even a brief duration, nephelometrically determined 24-h mean particle concentrations were nonsystematically distorted relative to gravitational data, 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 time-resolved particle measurements within 24-h samples. Precise, accurate interpretation of nephelometrically resolved short-term particle concentrations requires calibration based on short-term gravitational sampling.
使用固体燃料的农村家庭厨房构成了大多数人接触有害健康的空气污染物的微环境，尤其是可吸入颗粒物和一氧化碳。便携式浊度仪比仅靠重力法能更便宜、更精确地对农村家庭中的颗粒物进行时间分辨表征。然而，浊度仪的现场性能必须应对化学组成、大小和相对湿度变化很大的气溶胶。之前在住宅环境中对浊度仪性能的现场验证研究的是相对较低的颗粒物浓度，绝大多数24小时平均重力法测定的PM2.5浓度低于40微克/立方米。我们在中国污染严重的农村厨房中，研究了24小时重力法颗粒物测量值与个人数据记录仪（pDR）记录的浊度数据之间的关系，在这些厨房中，重力法测定的24小时平均可吸入颗粒物浓度高达700微克/立方米。我们发现，当相对湿度保持在95%以下时，尽管气溶胶混合复杂且环境条件多变，但浊度响应呈强线性关系。当相对湿度哪怕只是短时间超过95%时，相对于重力数据，浊度法测定的24小时平均颗粒物浓度会出现非系统性扭曲，而且同时进行的相对湿度测量和使用稳健的集中趋势统计量都无法提供校正方法。这种非系统性扭曲对于农村暴露评估研究来说尤其成问题，因为这类研究强调24小时样本内时间分辨颗粒物测量的上四分位数。要对浊度法分辨的短期颗粒物浓度进行精确、准确的解释，需要基于短期重力采样进行校准。
