These efforts have attenuated the emissions engendered by growth, but 24-hour PM10 (particulate matter with aerodynamic diameter less than 10 m) concentrations exceeding several hundred µg/m3 are still measured at many monitoring sites. 1,2 A persistent haze blankets the city, especially during winter, and there is great concern among residents and visitors about the effects of suspended particles on health. Aerosols that contribute to this visibility degradation are usually a combination of primary and secondary particles. Primary particles are directly emitted from different sources, while secondary particles form in the atmosphere from gaseous emissions of sulfur dioxide, oxides of nitrogen, ammonia, and heavy organic gases. Secondary aerosol formation may.
