Sampling artifacts of organic and inorganic aerosol: Implications for the speciation measurement of particulate matter

Sampling artifacts of organic carbon (OC) and nitrate were simultaneously evaluated in Beijing China during summer of 2010. It was demonstrated that the charcoal denuder used in this study can effectively remove not only the gaseous organics that could be adsorbed by quartz filter but also the gaseous HNO3 that could be adsorbed by nylon filter, giving rise to a new sampling method that using a charcoal denuder in combination with a quartz–nylon filter pack. Nitrate measured by the denuded quartz–nylon filter pack was approximately 1.5 times that of the value measured by the bare quartz filter, whereas comparison of organic carbon (OC) measured by the denuded and bare quartz filter showed that the OC concentration was overestimated by about 15% due to the positive sampling artifact. The new sampling method has the advantage that nitrate and OC can be accurately measured by a single sampling channel, thus it is suggested for the speciation monitoring of ambient particulate matter. It is also suggested that accurate measurement of nitrate is especially meaningful for China, because the NOx emissions continue to increase during the last decade.