Serious environmental problems have arisen alongside the rapid economic development of China, including the well-known issue of haze pollution. Not only does haze bring low atmospheric visibility, causing traffic-related problems, but it can also damage human health, and affect other aspects of the weather and climate, directly or indirectly. Secondary aerosol formation and rapid increases in aerosol particle sizes are believed to play important roles in haze formation. However, some simple but important questions remain unanswered: How frequently and how fast do fine aerosol particles grow? And what affects their rates of growth?