We assess the relationship among haze-fog, aerosol and meteorological conditions, and analyze the chemical compositions and sources of aerosol particles, as well make some suggestions for aerosol control strategy. Present-day haze and fog in China are both dependent on atmospheric aerosol loading and weather conditions. The secondary aerosol formation and changes, which dominate the total aerosol mass and are highly influenced by meteorological conditions, characterized the regional haze feature in East China. In the Huabei Plain, which suffers from intense haze and fog, secondary organic aerosols are found to have similar role like sulphate, contributing to aerosol mass during both new particle formation and aging stages. The organic aerosol mix with inorganic ones to form hygroscopic particles earlier at ～70% relative humidity (RH), but which have a small hygroscopic growth factor. The hygroscopic aerosol particles would also make the PM2.5 mass monitoring at China exhibiting unrealistic high concentration under high RH stage. About 70% of these particles are internally mixed with two or three different aerosol components. Most mineral particles are covered with visible coatings, including fly ash, soot and metal particles, leading to have more secondary aerosol formed on their surface. This complicates haze formation in China. Under high aerosol particle concentrations, greater numbers of cloud droplets with relative small-size are observed in low clouds relative to high clouds; and the associated aerosol impact on cloud microphysical processe is different in less polluted areas. At low supersaturation most of hygroscopic particles larger than 150 nm form cloud condensation nuclei (CCN), and the impact of aerosol chemical composition on CCN activation is significant. There is a high aerosol concentration in China relative to other areas in the world, except for urban South Asia. These particles form under complex conditions and interact with clouds, resulting that present-day haze and fog in China both are not natural phenomenon. Haze and fog reduces surface radiation, making the atmosphere more stable, resulting in continuous coagulation, condensation, accumulation of aerosol, and more CCN activation, leading to serious and maintained haze-fog events. The heavy and persistent haze-fog between 6 and 16 January 2013 in East China was caused by both high aerosol loading and singular static weather conditions. We need to have adequate scientific judgment on the complexity and expectation of aerosol emission reduction in China. The government needs to make informed decisions and implement laws to maintain the health of its people, but this is not easy when we strive for economic growth. There is no easy solution to control aerosol sources, but the government should spare no effort to cut aerosol and their precursors gas emission. Regional pollution control is also very critical; a strong policy and protocol needs to be enforced by the central government to drive provincial leaders to make the necessary changes to ensure better air quality and quality of life for the population.