To evaluate the impact of improved wood burning stoves on indoor air pollution, 53 homes in a rural town in Michoaca´n, Mexico, were selected from a health intervention study and monitored before and after receiving improved wood-burning stoves. Fine particulate matter F particles with aerodynamic diameter less than 2.5 mm (PM 2.5 ) F concentrations were measured in the central plaza of the community and in three microenvironments in the home (next to the stove, in the kitchen away from the stove, and outdoor patio). Forty-eight hour mean PM 2.5 concentrations in homes that burned wood in open fires were 693 mg/m 3 (95% CI: 246-1338) near the stove, 658 mg/m 3 (95% CI: 67-1448) in the kitchen away from the stove, and 94 mg/m 3 (95% CI: 36-236) on the patio. Mean ambient 24-h concentrations in the main plaza of the community were 59 mg/m 3 (95% CI: 29-92). Paired measurements before and after the installation of the Patsari improved wood-burning stove indicate a median 71% reduction in PM 2.5 concentrations near the stove and 58% reductions in kitchen concentrations, whereas patio and main plaza concentrations remain unaffected. Only 44% of participants reported to use their Patsari stoves exclusively during the transition period. Even with the predominant mixed use of the Patsari stove with open fires, estimated daily average personal exposures to PM 2.5 were reduced by 50%.

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The composition of urban dust can affect the health of urban populations, making it necessary to study its elemental composition and its sources. Our objectives were: a) to identify the main emission sources of heavy metals, and b) to evaluate the influence of land use and road type on the elemental composition of urban dust. 100 samples of urban dust taken in San Luis Potosí were analyzed using FRX. Descriptive statistics, Pearson's correlations coefficient, kriging interpolations, and analysis of variance were applied to the data. Cu and Zn were spatially associated with a metallurgical complex and, to a lesser extent, with an industrial park; Ca with fluorite and limestone industries, and Si with the surrounding soils. The highest concentrations of Cu, Zn, and Ca were found in mixed and industrial land uses. On the contrary, the highest concentrations of "natural elements" (Al, K, Si, Rb, and Y) were found in developable land and residential areas. The highest contents of Ca were found in secondary and primary roads. The conclusions were: a) the metallurgical complex is the main source of Cu and Zn, and b) the highest concentrations of Cu, Zn, and Ca were found in mixed and industrial land uses.

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