[Improvement and application of the method for determination of OCEC split]

Aerosol samples were collected in Beijing (BD) and Atlanta (GT) from July to August in 2011 using a Micro-Orifice Uniform Deposit Impactor (MOUDI) (0.18-18 microm, eight-stage) for organic carbon (OC) and elemental carbon (EC) measurement (Sunset Laboratory Inc, USA). The laser intensity of blank filters decreased with temperature in the process of OC & EC analysis because the structure of quartz filters was changed when burned which largely affected the determination of low concentration samples' splits. It would increase the accuracy of OC & EC split to determine it manually after the change of blank filter's laser intensity was recouped. The concentrations and size distributions of OC & EC using the improved method were different from taking the moment when oxygen was introduced as the split. The split may appear before oxygen addition, when the sample was rich in metal or substances that can be decomposed after heated. The concentrations of carbonaceous components were higher at BD than those at GT. The size distributions of OC showed a bimodal pattern with peaks appeared in the particles with size of (0.56-1.0) microm and (3.2-5.6) microm. The peak concentrations of OC were (2.82 +/- 1.59) microg x m(-3) and (1.95 +/- 0.76) microg x m(-3) at BD, and (1.28 +/- 0.41) microg x m(-3) and (0.64 +/- 0.19) microg x m(-3) at GT. EC showed a bimodal pattern at BD with peaks in particles with size of (0.56-1.0) microm and (3.2-5.6) microm, while showed a trimodal pattern at GT. The peak concentrations at BD were (0.32 +/- 0.24) microg x m(-3) and (0.26 +/- 0.19) microg x m(-3). EC at GT was preferably enriched in particles with size of (0.18-0.56) microm, the mass concentrations of EC in this size accounted for 44.6%. The OC and EC were more concentrated in accumulation mode at GT than those at BD, the reason may be that the main pollution source of GT is motor vehicle emission, while there are more industrial gas emissions at BD.