The primary aerosol sources include emissions from combustion, road or wind-blown dust, and plants, while the secondary formation processes include nucleation and growth by multiphase chemical processes.Also, primary and secondary particles undergo chemical and physical transformations and are subjected to cloud processing and transport in the atmosphere (8, 9).Reductions in emissions of the aerosol precursor gases from transportation and industry are essential to mediate severe haze pollution in China.As the world’s second largest economy, China has experienced severe haze pollution, with fine particulate matter (PM) recently reaching unprecedentedly high levels across many cities, and an understanding of the PM formation mechanism is critical in the development of efficient mediation policies to minimize its regional to global impacts.
The measured PM) demonstrate the presence of a higher number concentration of smaller particles during the clean period but a slightly lower particle number concentration of larger particles during the polluted period. 1During our observation period, southerly winds were most prevalent (50%), followed by winds from the northwest (42%) and northeast (7%) (Fig. The wind was much weaker from the south but stronger from the northwest and northeast.During the polluted period, the movement of the air mass is less than 50 km⋅d transport. 1 and 2 indicate that the aerosol nucleation and growth processes occur on the regional (several hundred kilometers) to urban (less than 100 km) scales, respectively, and local-scale phenomena, such as primary particle emissions by traffic, exert an insignificant impact on the particle mass growth.).The shaded colors denote the mass concentrations of the aerosol constituents, i.e., green for organics, blue for nitrate, red for sulfate, yellow for ammonium, purple for chloride, and black for black carbon.).The formation mechanisms leading to severe haze episodes with exceedingly high PM in Beijing has been suggested to be mainly from industrial pollution and secondary inorganic aerosol formation, but negligibly from traffic emissions (14).
In addition, meteorological conditions may govern regional and long-range transport of air pollutants (17, 18).
Accumulation of the particle mass concentration exceeding several hundred micrograms per cubic meter is accompanied by a continuous size growth from the nucleation-mode particles over multiple days to yield numerous larger particles, distinctive from the aerosol formation typically observed in other regions worldwide.