Ambient organic carbon to elemental carbon ratios: Influences of the measurement methods and implications

Ambient organic carbon (OC) to elemental carbon (EC) ratios include important information about the extent of secondary organic aerosol (SOA) production. Influences of the measurement methods on the OC to EC ratios were evaluated in Beijing. When analyzed by the IMPROVE-A temperature protocol, the presence of positive artifact would increase the OC to EC ratio by 14-36% based on the transmittance correction, whereas the ratio of the un-denuded filter was 1.12-1.31 times that of denuded filter when using the reflectance correction. The OC to EC ratios calculated by results from the transmittance correction showed more significant variation comparing with those based on the reflectance correction; and no correlation between them was found. SOA concentrations were predicted by the EC-tracer method to investigate effects of the charring correction methods. Estimated SOA based on the reflectance correction was found to be much lower comparing with that calculated by results from the transmittance correction. SOA based on the reflectance correction might be unreliable because it exhibited no correlation with water-soluble organic carbon (WSOC). On the other hand, WSOC and SOA based on the transmittance correction correlated well (R² = 0.77-0.94), indicating the secondary nature of WSOC in Beijing.