Characterization of carbonaceous aerosol by the stepwise-extraction thermal-optical-transmittance (SE-TOT) method

► OC is separated into extractable OC and un-extractable OC. ► Extractable OC is further isolated into non-polar, low-polar and high-polar OC. ► Low-polar and high-polar OC are strongly associated with SOA. ► Extractable OC is light-absorbing.