『Abstract
　In developing countries, aerosol particles damage the health of hundreds of millions of people. Migration from the country side to megacities increases emissions and exposure to particles. Some countries have started to limit emissions based on particulate mass, but this may increase particle number concentrations. In this study we discuss some earlier measurements carried out in the developing world and compare results from one-week measurement campaigns concerning the particle number size distribution and PM10 mass concentrations in New Delhi, India and Beijing, China. Our results show that submicron particle concentrations are high in both places. The average PM10 concentration was 360μg/m³ in New Delhi and 120μg/m³ in Beijing. The corresponding total particle number concentrations in the size range 3-800 nm were 63,000 cm^-3 and 35,000 cm^-3. Number and mass concentrations and their characteristics showed significantly different behaviour between these two locations, which stresses the importance of long-term simultaneous measurements of both quantities in different types of megacities.

Keywords: air pollution; aerosol particles; China; developing countries; India; number concentration』

1. Introduction
2. Aerosol particle concentrations in the developing world
　2.1. Sources of aerosol particles in developing countries
　2.2. Particulate mass concentrations
　2.3. Particle number concentrations
3. Case studies
　3.1. New Delhi, India
　3.2. Beijing, China
　3.3. Comparison between New Delhi and Beijing
4. Discussion and conclusions
Acknowledgments
References