Particle-bound PAH content in ambient air.

Area of Science:

• Environmental Chemistry
• Atmospheric Science
• Analytical Chemistry

Background:

• Polycyclic Aromatic Hydrocarbons (PAHs) are significant air pollutants originating from combustion processes.
• PAHs associate with atmospheric particles, influencing their environmental fate and transport.
• Understanding PAH distribution across particle sizes is crucial for assessing exposure and deposition.

Purpose of the Study:

• To characterize particle-bound PAH content in ambient air across different sites in southern Taiwan.
• To investigate the relationship between particle size and PAH concentration.
• To evaluate the contribution of gas and particle phases to PAH dry deposition.

Main Methods:

• Air sampling using dry deposition plates, Microorifice uniform deposited impactors (MOUDIs), Noll Rotary Impactor (NRI), and PS-1 samplers.
• Analysis of 21 individual PAHs using gas chromatograph/mass spectrometry (GC/MS).
• Particle size distribution analysis and dry deposition modeling.

Main Results:

• Sub-micron particles exhibited higher PAH content, attributed to soot composition and increased surface area for adsorption.
• Lower molecular weight PAHs showed greater gas-phase contribution to dry deposition flux compared to higher molecular weight PAHs.
• Dry deposition of PAHs was predominantly influenced by the gravitational settling of coarse particles (> 10 microm).

Conclusions:

• Particle-bound PAH levels vary significantly with particle size, with finer particles being more contaminated.
• Dry deposition models incorporating particle size distribution can effectively predict PAH deposition.
• Gravitational settling of coarse particles is the primary mechanism for PAH dry deposition.