Analysis of the Concentration of Gas-Phase and Solid-Phase Polyaromatic Hydrocarbons in Industrial Emissions from Aluminum Production

Aluminum production is one source of atmospheric polycyclic aromatic hydrocarbons (PAHs), of which benzo[a]pyrene is the best-studied representative. Other high-priority PAHs are attracting increasing attention for differentiation of PAH emissions and sources. Monitoring of these compounds is difficult because PAHs are present in both the solid-phase and gas-phase emissions (with the solid phase containing condensed PAHs); the gas-phase concentration of these substances depends on the manufacturing process temperature and the temperature of the environment. Atmospheric PAH emissions primarily originate from the pot-room ventilation skylights and gas-treatment-unit smokestacks. Low-molecularweight compounds dominate the gas emissions from the pot-room ventilation skylights and posttreatment emissions, while higher molecular weight compounds dominate the gas/dust/air mixture received for treatment. The gas/dust/air mixture received from the pot rooms for treatment by the gas treatment unit and discharged into the atmosphere through the smokestacks shifts the distribution of PAHs present in the atmosphere in favor of light, volatile compounds. The PAHs are close to uniformly distributed between the gas and solid phases of the gas/dust/air mixture emitted from the pot-room skylights. Over 70 wt.% of the PAHs in the emissions downstream of the gas treatment unit are in the gas phase, while the majority of the PAHs entering the gas treatment unit are in the solid phase. The resulting PAH distribution data for the gas/air mixture must be taken into account when developing the techniques for sampling the industrial emissions from the skylights and the atmospheric emissions downstream of the gas treatment unit during aluminum production.