2.1. Sampling site description and analysis In general, Bangladeshi rural and suburban households have a number of cooking arrangements. In many cases, kitchens are not enclosed by four walls and a ceiling. Some poor households do not have separate kitchens. Cooking during the rainy season takes place inside the single room with the adjacent space used by others in the household. During the dry season, cooking would be done outside the structure. In other houses, kitchens have three walls (i.e., the entrance is entirely open), with or without a roof. Some kitchens have four walls with gaps of a few inches between the walls and the roof. These structural arrangements are expected to have a significant effect on the particle concentrations in the kitchen and adjacent living area.
Sampling was conducted during the months of February and March 2006 in a rural area of Savar in the Dhaka district. Five houses were chosen depending on fuel use and kitchen configurations. Table 1 presents the characteristics of the kitchens that were selected as being representative of the variations in fuel use, cooking arrangements, and structural characteristics that affect ventilation. Before choosing these households, a survey was undertaken in which 33 individual households were surveyed to understand the lifestyle, household configurations, fuel use, etc. within the area of investigation. The information was then used to select these five different houses as representative of the households in the locality.
Five PM10 samples (four from the kitchen and one from the living room) were collected from each house using MiniVol Portable Air Samplers (AirMetrics, Eugene, OR, USA) [19]. The PM10 samples were collected in the kitchen over a 4 h interval from 7 a.m. to 11 a.m. covering the cooking period and for 8 h from 7 a.m. to 3 p.m. in the living area of each selected household. One collocated PM2.5 sample was also collected for 4 h period along with PM10 from each kitchen in order to estimate the PM10/PM2.5 ratio for the different types of fuels typically used in these kitchens. PM10 samples were also collected outside the house during sampling period to assess the influence of ambient air pollution on indoor air quality.
The MiniVols were programmed to sample at 5 l/min through PM10 and PM2.5 particle size separators (impactors) and then through 2 mm pore Teflon filters. The actual flow rate should be 5 l/ min (Lpm) at ambient conditions for proper size fractionation. To ensure a constant flow of 5 Lpm through the size separator at different air temperatures and atmospheric pressures, the sampler flow rates were adjusted for the ambient conditions at the sampling site. The sampler was placed in the room with the nozzle at approximately the height of the breathing zone.
2.1.1. PM mass determination PM mass was measured by the Chemistry Division of the Atomic Energy Centre, Dhaka (AECD). The PM10 and PM2.5 samples were determined by weighing the filters before and after exposure using a microbalance (METTLER Model MT5). The filters were equilibrated for 24 h at constant humidity of 50% and temperature (22 C) in the balance room before every weighing. A Po-210 (alpha emitter) electrostatic charge eliminator (STATICMASTER) was used to eliminate the static charge accumulated on the filters before each weighing. The difference in weights for each filter was calculated and the mass concentrations for each PM2.5 or PM10 sample were then determined. The concentration of black carbon (BC) in the fine fraction of the samples were determined by reflectance measurement using an EEL type Smoke Stain Reflectometer.
2.1.2. Elemental analysis A radioisotope-induced energy-dispersive X-ray fluorescence (EDXRF) spectrometer was used to analyze the elemental composition of all of the filter samples. Energy-dispersive X-ray Fluorescence (EDXRF) analysis directly measures the energy as well as the intensity of the fluoresced X-rays. EDXRF analysis was based on emissions from a Cd-109 source (emitting Ag–K X-rays). The EDXRF spectra were processed and quantified using the Qualitative X-ray Analysis System (QXAS) and the Analysis of X-ray spectra by Iterative Least square fitting (AXIL). Calibration was performed using MicroMatter thin elemental standards (MicroMatter Co., Eastsounds, WA, USA). Because of the limitations of the XRF system, only eight elements: K, Ca, Ti, Cr, Mn, Fe, Cu and Zn could be determined.