Many urban households in developing countries use biomass fuels for cooking. The proportion of household biomass use varies among neighborhoods, and is generally higher in low socioeconomic status (SES) communities. Little is known of how household air pollution varies by SES and how it is affected by biomass fuels and traffic sources in developing country cities. In four neighborhoods in Accra, Ghana, we collected and analyzed geo-referenced data on household and community particulate matter (PM) pollution, SES, fuel use for domestic and small-commercial cooking, housing characteristics, and distance to major roads. Cooking area PM was lowest in the high-SES neighborhood, with geometric means of 25 (95% confidence interval, 21-29) and 28 (23-33) μg/m 3 for fine and coarse PM (PM 2.5 and PM 2.5-10 ), respectively; it was highest in two low-SES slums, with geometric means reaching 71 (62-80) and 131 (114-150) μg/m 3 for fine and coarse PM. After adjustment for other factors, living in a community where all households use biomass fuels would be associated with 1.5-to 2.7-times PM levels in models with and without adjustment for ambient PM. Community biomass use had a stronger association with household PM than household's own fuel choice in crude and adjusted estimates. Lack of regular physical access to clean fuels is an obstacle to fuel switching in low-income neighborhoods and should be addressed through equitable energy infrastructure. sustainable development | urbanization | global health | household energy | Africa T he populations of cities in the developing world are growing, with sub-Saharan Africa having the highest urban population growth rate worldwide (1). Some urban environmental health risks in the developing world are similar to those in high-income countries, such as the role of transportation as a determinant of particulate matter (PM) pollution levels and spatial patterns (2-5). Urban environmental health risks in developing countries also have some unique features, including high exposure to multiple risks in low-income "slum" neighborhoods (6, 7). A feature of urban PM pollution that, with few exceptions, is unique to developing countries is the widespread household use of biomass fuels (8, 9). Therefore, PM pollution in urban homes may be because of household or neighborhood biomass use in addition to sources that are also found in high-income countries, such as transportation and industrial pollution.The patterns and sources of indoor air pollution in high-income countries have been studied (10-12). There is also increasing attention to residential indoor air quality in developing countries, including the concentrations of various pollutants, their sources, and the role of ventilation (13-15). However, most current studies of biomass fuels and household air pollution in developing countries have focused on the indoor environment in rural areas, where biomass is the most common or even universal household fuel. There are few studies of household PM in developing country cities, especially in ...