Humidity and gravimetric equivalency adjustments for nephelometer-based particulate matter measurements of emissions from solid biomass fuel use in cookstoves.

Sutyajeet Soneja,Frank Curriero,William Checkley,James Tielsch,Joanne Katz,Patrick Breysse,Chen Chen,Scott Zeger

doi:10.3390/ijerph110606400

Abstract

Great uncertainty exists around indoor biomass burning exposure-disease relationships due to lack of detailed exposure data in large health outcome studies. Passive nephelometers can be used to estimate high particulate matter (PM) concentrations during cooking in low resource environments. Since passive nephelometers do not have a collection filter they are not subject to sampler overload. Nephelometric concentration readings can be biased due to particle growth in high humid environments and differences in compositional and size dependent aerosol characteristics. This paper explores relative humidity (RH) and gravimetric equivalency adjustment approaches to be used for the pDR-1000 used to assess indoor PM concentrations for a cookstove intervention trial in Nepal. Three approaches to humidity adjustment performed equivalently (similar root mean squared error). For gravimetric conversion, the new linear regression equation with log-transformed variables performed better than the traditional linear equation. In addition, gravimetric conversion equations utilizing a spline or quadratic term were examined. We propose a humidity adjustment equation encompassing the entire RH range instead of adjusting for RH above an arbitrary 60% threshold. Furthermore, we propose new integrated RH and gravimetric conversion methods because they have one response variable (gravimetric PM2.5 concentration), do not contain an RH threshold, and is straightforward.

Highlights

Assessment of exposure-disease relationships related to use of solid biomass fuels for cooking and other household energy needs in the developing world has become a top priority [1]
Richards et al utilized heaters attached to the inlet of nephelometers to eliminate the influence on particulate matter (PM) measurements from high relative humidity (RH) levels [6], while Wu et al questioned the ability of the heater attached to the inlet to remove the influence from high RH [8]
For Equation (1b), we fitted Equation (1) with our data collected in the mock house and occupied homes, where the correction factor was calculated as the ratio of average pDR-1000 PM concentration and the corresponding gravimetric PM2.5 concentration

Summary

Introduction

Assessment of exposure-disease relationships related to use of solid biomass fuels (wood, dried animal manure, and crop residue) for cooking and other household energy needs in the developing world has become a top priority [1]. With approximately 3 billion people using solid biomass fuels, large scale interventions using new, more efficient cooking technologies are being conducted to reduce adverse health effects associated with solid biomass fuel use [1,2]. The success of these efforts will hinge in part on the degree to which new stove technology reduces pollutants and the corresponding reduction in disease. To account for the influence of relative humidity (RH) in nephelometric measurements, a correction factor is typically applied. Since filter-based monitors incorporate a humidity equilibration step in the weighing process, paired gravimetric and nephelometer samples are more commonly used to estimate humidity correction factors

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Conclusion