Volatility Dependence of the Aerosol Size Distributions of Nonpolar Organic Compounds : A Case Study in Shanghai

The aerosol size distribution of organic compounds is one of the fundamental characteristics that regulates their atmospheric deposition and environmental fate. In this study, we characterized the organic components (mostly nonpolar organic compounds) in size-resolved particles, with a focus on polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (O-PAHs), n-alkanes, and polybrominated diphenyl ethers (PBDEs), in the urban Shanghai atmosphere during a 1-year sampling period using gas chromatography (GC) coupled to tandem mass spectrometry (GC-MS/MS) and two-dimensional GC with a flame ionization detector (GC × GC-FID). These compounds ranged from volatile organic compounds (VOCs) to extremely low volatility organic compounds (ELVOCs). We related their aerosol size distributions with their volatilities. On average, high positive correlations (p < 0.01) were observed between the size distribution characteristics (e.g., geometric mean diameter [GMD] and mass fraction in coarse particles) and volatility (logarithmic value of the saturation mass concentration, log C^*) for the compounds that we examined. A higher ambient temperature tends to increase the slope of the regression line between size distribution and volatility (log C^*). Further dry deposition modeling of size-resolved particles showed a positive correlation (p < 0.01) between the bulk dry deposition velocity and GMD and between the bulk dry deposition velocity and volatility of the target compounds, indicating that low-volatility organic compounds have a lower dry deposition velocity and are more likely to be transported to remote areas if they do not have a short half-life in the atmosphere.