Source and variation of carbonaceous aerosols at Mount Tai, North China: Results from a semi-continuous instrument

Carbonaceous aerosols were measured with a semi-continuous thermal-optical OC/EC analyzer at the summit of Mount Tai (1532.7m a.s.l) in north China during spring and summer of 2007. Non-volatile organic carbon (NVOC) and elemental carbon (EC) showed high concentrations with mean values of 6.07, 1.77 and 5.05, 0.99μgm-3in spring and summer, respectively. The mean concentration of semi-volatile organic carbon (SVOC) was 6.26μgm-3in spring and 13.33μgm-3in summer, contributing 51 and 72% to total organic carbon (TOC), respectively. Different measurement methods for EC were compared, and a good agreement between optical and thermal methods was found. Due to volatilization of SVOC during sampling, the integrated filter measurement without denuder and backup absorbent tended to underestimate TOC compared to semi-continuous measurement. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) results indicated that the observed carbonaceous aerosols at Mount Tai were mostly contributed by the transport of aged aerosols in the planetary boundary layer (PBL) mixed with combined sources. Also, the influence of emissions from Korea was observed at Mount Tai, as well as biomass burning. Cloud processing contributed to elevated SVOC concentrations, and the formation of secondary organic aerosol (SOA) through photochemistry and cloud processing were both enhanced in summer. Clean air masses from the free troposphere reduced carbonaceous concentrations, and the regional background condition with 2.13±1.05μgm-3of NVOC, 0.43±0.29μgm-3of EC, and 2.40 to 6.80μgm-3of SVOC (for spring and summer, respectively) were suggested for the North China Plain.