Abstract：To evaluate the chemical profiles and sources of spring aerosol over Xi'an, 24 h a day fine particulate matter PM_2.5 and inhalable particulate matter PM₁₀ samples were collected at 4 urban sites simultaneously in 2 weeks using minival samplers. PM_2.5 and PM₁₀ mass concentrations, carbon analyses (organic and elemental carbon) , water inorganic ion (NH₄ ⁺, Na^+, K⁺, Ca²⁺, Mg²⁺, F^-, Cl^-, SO₄ ^2-, NO₃^-) and trace elements (Ca and Fe) were determined by gravimetry, ion chromatography, thermal-optical carbon analyzer and ED-XRF spectrometry, respectively. The results show that the average mass concentration of PM10 is 3 times larger than that of PM_2.5. Comparing with that in the non-dust period a sharp increase in organic carbon level is observed during the dust period. SO₄ ^2--NO₃^--NH₄ ⁺concentration is much higher in dust storm events than in normal days, mainly due to dilution of enhanced particulates in dry dust storm. The transport pathways and sources of PM_2.5 and PM₁₀ in dust storm period are identified on the basis of the air mass trajectories and the ratio of Ca and Fe elements. CO₃ ^2-concentration is estimated using the method of ion balance. A strong relationship is observed between evaluated CO₃ ^2-and measured Ca²⁺, which indicates that CaCO₃ is a main composition during dust storm period.

Keywords：fine particulate matter (PM_2.5) ; inhalable particulate matter (PM₁₀) ; dust storm