Influence of Seasonal Variation and Long-Range Transport of Carbonaceous Aerosols on Haze Formation at a Seaside Background Site, China

ABSTRACT

The Yellow River Delta is a crucial background site that is located in a heavily polluted area in China. Carbonaceous aerosol concentrations were measured using 2.5-μm-diameter particle (PM_2.5) samples collected from the Yellow River Delta, Shandong Province, China, from January 2011 to November 2011 by using the thermal/optical reflectance method. In the Yellow River Delta, the organic carbon (OC) concentration ranged from 0.74 to 27.51 μg/m³; the annual average concentration was 7.61 μg/m³. Moreover, the elemental carbon (EC) concentration ranged from 0.16 to 15.00 μg/m³; the annual average concentration was 2.98 μg/m³. In addition, the carbonaceous aerosols concentrations were the highest in winter and lowest in summer. The EC tracer method showed that the secondary OC (SOC) contribution to the total carbonaceous concentration tended to be higher in winter than in other seasons. An analysis of carbonaceous showed that haze was derived from different matter in different seasons, particularly haze in winter was dominated by OC, EC, and SOC. The Yellow River Delta can be considered a background site because of the strong correlation between OC and EC (R² = 0.83–0.97). Furthermore, the OC/EC ratios for cold seasons (winter and spring) were higher than those for warm seasons (summer and autumn), suggesting that the OC originated from biomass burning in nearby villages in cold seasons. Back trajectories indicated that short-distance air mass from region area contribute most to the sample site. However, the highest carbon concentrations during haze days were related to the air mass travelled through the Bohai rin Rim except in summer haze episodes. Based on the entire sampling period, the air mass travelled through the polluted areas of Beijing and Hebei Province toward the Yellow River Delta may contribute most to carbonaceous species due to long-range transport.