PM_2.5 samples were collected daily at the Lin'an regional background station (LA) in Zhejiang, China during 2014–2015 and the major chemical components including organic carbon (OC), elemental carbon (EC) and water-soluble inorganic ions (WSII) were determined. Backward trajectory clustering and potential source contribution function (PSCF) were adopted for identifying the transport pathways and potential source regions of PM_2.5 at LA. The annual mean concentration was 68.9 ± 28.3 μg m⁻³, indicating severe pollution in East China. Obvious seasonal variations were found, with highest level in winter and lowest in summer. Carbonaceous aerosols and WSII were the predominant compositions, accounting for 30.7% and 53.5% of PM_2.5, respectively. Secondary inorganic ions (SO₄²⁻, NO³⁻, and NH₄⁺) made a total contribution of 45.2% to PM_2.5. Heterogeneous formation played a dominant role in SO₄²⁻ formation and NH₄⁺ formation promoted NO³⁻ formation. Stationary sources played a more important role than mobile sources based on NO³⁻/SO₄²⁻ ratio of 0.53. Aerosol environment at LA was ammonium-poor and SO₄²⁻ was only neutralized sufficiently by NH₄⁺ with the predominant production of (NH₄)₂SO₄ in winter. Four major transport pathways of air masses at LA were found based on trajectory clustering. Air masses from the northwest Gobi areas passing over the heavily polluted regions in North and Central China had the highest levels of PM_2.5, followed by the air masses from Central China. PSCF results suggested that surrounding areas in the Yangtze River Delta region were major regional origins of PM_2.5 and its major components. Northern region was an important origin for carbonaceous components, and southwestern region was significant for secondary inorganic ions. This study helps understand PM_2.5 characteristics, identify potential source regions and effectively control PM_2.5 in East China.