Distribution and origin of carbonaceous aerosol over a rural high-mountain lake area, Northern China and its transport significance

PM2.5 and TSP samples were collected at Lake Daihai, a rural high-mountain area in China, in four seasons during 2005–2007. Organic carbon (OC), elemental carbon (EC), char-EC, and soot-EC were analyzed using the thermal/optical reflectance (TOR) method with different temperature plateaus and oxidation atmospheres. TC, OC, EC, and char-EC concentrations of TSP and PM2.5 showed seasonal variations with the highest concentrations in winter and the lowest in summer, while soot-EC reveals a little different variation, with the highest concentration in spring, indicating different source contributions from other parameters. OC/EC correlations were weaker at Daihai than those from urban areas. Although little differences existed in TSP and PM2.5, average OC/EC ratios varied seasonally and ranged from 9.0 in winter to 5.0 in spring. Char-/soot-EC ratios showed similar pattern, with the highest average ratios (>3.0) in winter, consistent with the contributions from residential biomass burning and coal combustion. Back trajectories related the highest carbon concentrations with the southeasterly air masses and the lowest carbon levels with northward flows.