Aerosol lead and associated elements in Beijing, China

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Urban Pollution

Background:

• Urban atmospheres contain fine and coarse aerosol particles.
• Lead and associated elements are significant urban air pollutants.

Purpose of the Study:

• To determine the relative importance of local versus regional sources for lead and associated elements in Beijing's urban aerosol.
• To differentiate between fine and coarse particle contributions to heavy metal pollution.

Main Methods:

• Aerosol sampling at five distinct urban locations in Beijing using cascade impactors.
• Elemental analysis of aerosol samples via proton induced X-ray emission (PIXE).
• Comparison of Beijing data with published data from St. Louis, USA.

Main Results:

• Fine particles (<2 μm) primarily contained lead (Pb), zinc (Zn), arsenic (As), and copper (Cu), with concentrations unrelated to traffic, suggesting regional combustion sources.
• Coarse particles (>2 μm) showed concentrations of dust constituents (Si, Al, Ca) increasing with traffic intensity.
• Enrichment factors for Pb, Zn, and Cu in urban Beijing's coarse particles were significantly higher than in nonurban areas, indicating surface dust contamination.
• Comparison with St. Louis revealed similar fine and coarse Pb concentrations but lower Zn, Ca, and Fe in Beijing; both cities showed greater enrichment than Earth's crust.

Conclusions:

• Heavy metals from combustion are present as fine particles and reentrained coarse particles in urban air.
• Both fine and coarse particle fractions contribute to human exposure to heavy metals.
• Urban surface dust is a significant reservoir for heavy metals, originating from both deposition and local re-suspension.