Identification of secondary organic aerosol episodes and quantitation of primary and secondary organic aerosol concentrations during SCAQS

Two-hour average organic and elemental carbon concentrations from the 1987 Southern California Air Quality Study were used to gain an understanding of the dynamics of organic aerosol formation and to quantify secondary organic aerosol concentrations. Five episodes of secondary organic aerosol formation occurred during the summer study. During these periods secondary organic aerosol at Claremont typically peaked between 1600 and 1800 Pacific Daylight Time, and this peak was often 1–2 h after the ozone peak. Primary organic aerosol dominated with the exception of several hours in the afternoon. However, during these afternoon periods as much as 80% of the organic aerosol was secondary. Concentrations of secondary organic aerosol as high as 14 μgC m−3 were observed on some days. Interestingly, the highest concentrations of secondary organic aerosol occurred on Saturdays.