Positive sampling artifacts of organic carbon fractions for fine particles and nanoparticles in a tunnel environment

The positive artifacts in particulate organic carbon fractions for fine particles (PM _2.5) and nanoparticles (PM _0.1) were characterized in a tunnel environment by using the QBQ (a quartz filter behind a quartz filter) method. The OC concentrations of the backup quartz filters ranged from 3.56 to 11.38μgm ^-3 with the average of 6.70μgm ^-3 for PM _2.5, and from 2.62 to 7.27μgm ^-3 with the average of 4.64μgm ^-3 for PM _0.1. The most abundant species on the backup quartz filters was OC1 for both PM _2.5 and PM _0.1, accounting for 56.9% and 41.1% of the measured organic carbon, respectively. Most of EC fractions (EC1-EC3) on the backup filters for PM _2.5 and PM _0.1 were below the minimum detection limit. Therefore, only OC contributed to positive artifacts distinctly with the average percentage of 21.7% and 48.0% for PM _2.5 and PM _0.1, respectively. The artifacts for four organic carbon fractions ranged from 36.1% (OC1) to 4.4% (OC4) for PM _2.5 and from 68.0% (OC1) to 31.9% (OC4) for PM _0.1. The uncorrected OC/EC ratios on the front quartz filters were higher by as much as 30% and 107% for PM _2.5 and PM _0.1 than those corrected for positive organic artifacts, respectively. That is, much higher percentage of positive artifacts was found for PM _0.1 OC fractions on the front filters. The comparison of the present and previous studies shows that OC positive artifacts vary widely among various PM fractions and sampling sites attributing to many factors that are worth investigating in the future.