Watson John G, Chow Judith C, Chen L W Antony, Frank Neil H
Division of Atmospheric Sciences, Desert Research Institute, Reno, NV 89512, USA.
J Air Waste Manag Assoc. 2009 Aug;59(8):898-911. doi: 10.3155/1047-3289.59.8.898.
Volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) adsorb to quartz fiber filters during fine and coarse particulate matter (PM2.5 and PM10, respectively) sampling for thermal/optical carbon analysis that measures organic carbon (OC) and elemental carbon (EC). Particulate SVOCs can evaporate after collection, with a small portion adsorbed within the filter. Adsorbed organic gases are measured as particulate OC, so passive field blanks, backup filters, prefilter organic denuders, and regression methods have been applied to compensate for positive OC artifacts in several long-term chemical speciation networks. Average backup filter OC levels from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network were approximately 19% higher than field blank values. This difference is within the standard deviation of the average and likely results from low SVOC concentrations in the rural to remote environments of most IMPROVE sites. Backup filters from an urban (Fort Meade, MD) site showed twice the OC levels of field blanks. Sectioning backup filters from top to bottom showed nonuniform OC densities within the filter, contrary to the assumption that VOCs and SVOCs on a backup filter equal those on the front filter. This nonuniformity may be partially explained by evaporation and readsorption of vapors in different parts of the front and backup quartz fiber filter owing to temperature, relative humidity, and ambient concentration changes throughout a 24-hr sample duration. OC-PM2.5 regression analysis and organic denuder approaches demonstrate negative sampling artifact from both Teflon membrane and quartz fiber filters.
在分别针对细颗粒物和粗颗粒物（PM2.5和PM10）进行热/光碳分析以测量有机碳（OC）和元素碳（EC）的采样过程中，挥发性有机化合物（VOCs）和半挥发性有机化合物（SVOCs）会吸附到石英纤维滤膜上。采集后，颗粒态SVOCs可能会挥发，其中一小部分会吸附在滤膜内。吸附的有机气体被计为颗粒态OC，因此，在多个长期化学形态监测网络中，已采用现场空白样、备用滤膜、前置滤膜有机去除器和回归方法来补偿正OC假象。来自保护视觉环境跨部门监测（IMPROVE）网络的备用滤膜OC平均水平比现场空白样值高出约19%。这种差异在平均值的标准偏差范围内，很可能是由于大多数IMPROVE站点处于农村到偏远环境中SVOC浓度较低所致。来自城市（马里兰州米德堡）站点的备用滤膜显示其OC水平是现场空白样的两倍。将备用滤膜从顶部到底部进行切片显示，滤膜内OC密度不均匀，这与备用滤膜上的VOCs和SVOCs与前置滤膜上的相等这一假设相反。这种不均匀性可能部分是由于在24小时采样期间，由于温度、相对湿度和环境浓度变化，前置和备用石英纤维滤膜不同部位的蒸汽发生蒸发和再吸附所致。OC-PM2.5回归分析和有机去除器方法证明了来自聚四氟乙烯膜和石英纤维滤膜的负采样假象。
