Personal exposures to fine particulate matter and black carbon in households cooking with biomass fuels in rural Ghana

Abstract

Objective: To examine cooking practices and 24-h personal and kitchen area exposures to fine particulate matter (PM2.5) and black carbon in cooks using biomass in Ghana.

Methods: Researchers administered a detailed survey to 421 households. In a sub-sample of 36 households, researchers collected 24-h integrated PM2.5 samples (personal and kitchen area); in addition, the primary cook was monitored for real-time PM2.5. All filters were also analyzed for black carbon using a multi-wavelength reflectance method. Predictors of PM2.5 exposure were analyzed, including cooking behaviors, fuel, stove and kitchen type, weather, demographic factors and other smoke sources.

Results: The majority of households cooked outdoors (55%; 231/417), used biomass (wood or charcoal) as their primary fuel (99%; 412/413), and cooked on traditional fires (77%, 323/421). In the sub-sample of 29 households with complete, valid exposure monitoring data, the 24-h integrated concentrations of PM2.5 were substantially higher in the kitchen sample (mean 446.8 µg/m3) than in the personal air sample (mean 128.5 µg/m3). Black carbon concentrations followed the same pattern such that concentrations were higher in the kitchen sample (14.5 µg/m3) than in the personal air sample (8.8 µg/m3). Spikes in real-time personal concentrations of PM2.5 accounted for the majority of exposure; the most polluted 5%, or 72 min, of the 24-h monitoring period accounted for 75% of all exposure. Two variables that had some predictive power for personal PM2.5 exposures were primary fuel type and ethnicity, while reported kerosene lantern use was associated with increased personal and kitchen area concentrations of black carbon.

Conclusion: Personal concentrations of PM2.5 exhibited considerable inter-subject variability across kitchen types (enclosed, semi-enclosed, outdoor), and can be elevated even in outdoor cooking settings. Furthermore, personal concentrations of PM2.5 were not associated with kitchen type and were not predicted by kitchen area samples; rather they were driven by spikes in PM2.5 concentrations during cooking. Personal exposures were more enriched with black carbon when compared to kitchen area samples, underscoring the need to explore other sources of incomplete combustion such as roadway emissions, charcoal production and kerosene use.

Keywords: Biomass; Black carbon; Cooking; Fine particulate matter; Personal exposure.

Fig. 1

Black carbon concentrations for personal and area samples across households reporting kerosene lantern use and households reporting no kerosene lantern use during exposure monitoring period. A fractional polynomial fit was used to allow a semi-quantitative comparison of black carbon exposures as a function of PM_2.5 level indicating that both personal and kitchen samples were similarly enriched by black carbon when kerosene use was reported.

Fig. 2

Correlation between real-time and integrated measurements of PM_2.5 concentrations (slope=1.6, Spearman rho=0.9, p<0.00001; n=29).

Fig. 3

Panel of 24-h real-time PM2.5 concentrations in nine households stratified by kitchen type (enclosed, semi-enclosed, outdoor/open).

Photo 1

Area air sampling system in weatherproof case during 24-h monitoring period of an outdoor kitchen.

Photo 2

Personal air sampling system including Triplex cyclone, Personal Data Ram, battery operated TSI Sidepak SP530, and waist pack.

Photo 3

Personal air sampling system as worn by study participants. The Personal Data Ram and TSI Sidepak SP530 are fitted in waist pack while the Triplex cyclone remains near breathing zone.