Volckens John, Leith David
Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, 27599-7431, USA.
Environ Sci Technol. 2002 Nov 1;36(21):4613-7. doi: 10.1021/es020711s.
Adsorptive and evaporative artifacts often bias measurements of semivolatile aerosols. Adsorption occurs when the sampling method disrupts the gas-particle partitioning equilibrium. Evaporation occurs because concentrations of semivolatiles are rarely constant over time. Filtration is subject to both adsorptive and evaporative artifacts. By comparison, electrostatic precipitation reduces these artifacts by minimizing the surface area of collected particles without substantially disrupting the gas-particle equilibrium. The extent of these artifacts was determined for filter samplers and electrostatic precipitator samplers for semivolatile alkane aerosols in the laboratory. Adsorption of gas-phase semivolatiles was lower in electrostatic precipitators by factors of 5-100 compared to the filter method. Particle evaporation from the electrostatic sampler was 2.3 times lower than that from TFE-coated glass-fiber filters. Use of a backup filter to correct for compound-specific adsorption artifacts can introduce positive or negative errors to the measured particle-phase concentration due to competition among the adsorbates for available adsorption sites. Adsorption of evaporated particles from the front filter onto the backup filter increased the measured evaporative artifact by a factor of 1.5-2.
吸附和蒸发伪像常常会使半挥发性气溶胶的测量产生偏差。当采样方法破坏气-粒分配平衡时，就会发生吸附现象。蒸发现象的发生是因为半挥发性物质的浓度随时间很少保持恒定。过滤会受到吸附和蒸发伪像的影响。相比之下，静电沉淀通过将收集到的颗粒表面积降至最低且基本不破坏气-粒平衡，从而减少了这些伪像。在实验室中，针对半挥发性烷烃气溶胶的过滤器采样器和静电沉淀采样器，确定了这些伪像的程度。与过滤法相比，静电沉淀器中气相半挥发性物质的吸附量低5至100倍。静电采样器的颗粒蒸发量比涂有TFE的玻璃纤维过滤器低2.3倍。使用备用过滤器来校正特定化合物的吸附伪像，由于被吸附物之间对可用吸附位点的竞争，可能会给测量的颗粒相浓度带来正误差或负误差。从前置过滤器蒸发的颗粒吸附到备用过滤器上，使测量的蒸发伪像增加了1.5至2倍。
