Mixing of mineral with pollution aerosols in dust season in Beijing: Revealed by source apportionment study

Abstract

A detailed systematic aerosol source apportionment study was performed with two intensive sampling campaigns in the spring dust storm seasons of 2001 and 2002 in Beijing, China. The concentrations of 23 elements and 15 ions and the total mass in 115 total suspended particulate (TSP) samples were measured. Combining enrichment factors, elemental signatures, back trajectory analysis, bilinear positive matrix factorization (PMF2) analysis with the meteorological pattern, the mixing of mineral aerosol with pollution aerosol and their apportionments in different dust episodes were elucidated. Ca/Al was proved to be a good signature to trace different dust origin areas. Soil dust, road dust, secondary, industrial/coal combustion, salts, phosphates, nitrites, and oil combustion were identified by PMF to be the eight main sources. Soil dust (from outside) increased sharply when cold front intruded Beijing in dust events (∼80-95% of total dust), which neutralized local acidic aerosol. Road dust (from local by re-suspension) contributed 15-30% of the total TSP. Intruded dusts brought lots of sulfate (from soil containing high-S or from pollutants introduced on the pathway) but little nitrate. The secondary sulfate/nitrate and the total pollutants contributed 25% and 40-50%, respectively, of the TSP in those dust episodes, which were transported in lower layer and mixed strongly with local re-suspended pollution aerosols. Sulfur/Nitrogen oxidation ratios in dust storms and in non-dust storms were <2% and 10-40%, respectively, and had a little jumps just after dust peaks, which indicated that dust provided a good basic surface for the heterogeneous reactions. © 2008 Elsevier Ltd. All rights reserved.