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The filter sample of aerosol,ion chromatogram and therm-optical transmission are used to obtain spectral analysis of aerosol constituents from July 2007 to March 2008.The minimum OC/EC ratio is used to calculate the primary and secondary organic carbon and the extinction effect of the quota of the secondary aerosol on visibility is estimated.As indicated in the analysis,the mass of secondary aerosol takes up 50% of the total mass of PM2.5; the OC/EC ratio is larger than 2 and there are significant characteristics of secondary aerosol generation; the quotas of secondary OC are comparable with those of sulphate and there is obvious enrichment of secondary aerosol under the condition of relative pollution.In a dry environment,the extinction weight is 59% for the secondary aerosol while being as high as 82% if the environment is highly humid (RH=95%).The hygroscopic growth of the aerosol can reduce visibility greatly,the secondary aerosol shares much larger quotas with relative pollution.For the Pearl River Delta (PRD),secondary aerosol and carbonaceous aerosol,especially secondary organic carbon (SOC),are a very acute problem; the study of the generating mechanism and sources for secondary aerosol are the keys to the effort of controlling visibility in this region.The equation set forth in IMPROVE experiments can only be referenced but not applicable to evaluate the extinction effect of aerosol compositional spectra on visibility in the PRD region.