| Abstract
| - Although sampling artifacts of acidity, ammonium, nitrate,and chloride in airborne particulate pollutants can bereduced by the use of denuders to absorb interfering gases,artifacts due to interparticle interactions still remain. Inthis study, the contribution of individual artifact reactionsto particle evaporation and the effects of aerosolcomposition on the extents of sampling artifacts in PM2.5were investigated. Samples were collected using a Harvardhoneycomb denuder/filter-pack system at an urban siteand a rural site in Hong Kong. The results show that theformation of artifacts can be categorized into two regimes: ammonium rich (AR) samples with a molar ratio [NH4+]/[SO42-] greater than 1.5 and ammonium poor (AP) sampleswith a molar ratio [NH4+]/[SO42-] less than or equal to1.5. The urban samples were all AR samples, and they werecharacterized by high nitrate and low in situ free acidconcentrations. In contrast, the rural samples were all APsamples and they were characterized by low nitrate andhigh in situ free acid concentrations. We have developed amethodology to estimate the contribution of each artifactreaction to the sampling loss of nitrate, chloride, ammonium,and acidity. In the AR samples, the evaporation of HNO3and HCl and concomitant evaporation of NH3 were the principalreactions in determining the extent of the sampling lossof nitrate and chloride. In the AP samples, the evaporationof HNO3 and HCl alone was the principal reaction instead,especially at high sampling loss. The in situ free acidconcentration, a function of aerosol composition and ambientconditions, is a more useful parameter than strongacidity in understanding the sampling loss of acidity,nitrate, and chloride from the collected particles.
|
